15. Alerts, Notifications, Application Lifecycle.srt

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Stanford University. >> Well,
>> 斯坦福大学 >> 好

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welcome to Stanford CS193P, fall of 2017 and
欢迎来到斯坦福 CS193P 2017-18 年秋季学期

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18's Lecture number 15. And today we have three topics for
这是第十五节课。我们今天有三个内容要讲

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you, one is Alerts and Action Sheets. So that's a way of

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kind of notifying the user when an extraordinary event

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happens, or to help your user make a branching decision

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where to go now in the app, where it's kind of, you know,

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two or three choices of where they can go.

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The second thing we're gonna talk about is Notifications

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and KVO, that's a way of communicating blind and

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structured inside of our MVC and then finally,

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I'm gonna talk about the Application Lifecycle.

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We already talked about the view controller lifecycle,

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now we're gonna talk about the lifetime of your application.

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All right, so let's start with Alerts and

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Action Sheets. These two things are very similar,

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the API to use them is almost identical, so I always talk

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about them together. They're a little bit different,

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an alert, it pops up in the middle of the screen.

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They're both modal, they kinda take over your screen but,

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alert pops up in the middle.

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Generally, whatever the alert is telling you or asking you,

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you're only gonna have one or maybe two choices to respond.

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It would be unusual to have an alert, even with three buttons

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in it. It's usually for asynchronous things,

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things like a network failure or something that happens out

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of the ordinary. You don't wanna use an alert as just

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a way to talk to your user and ask them a yes or no question,

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things like that. Alerts are pretty disruptive to the user

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interface experience because they lock out the entire app

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and force you to deal with this thing.

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So it's not a primary,

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kind of user interface element,

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it's more of an emergency situation, asynchronous,

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unusual, that kind of thing. Now an action sheet is similar

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in that it's modal, takes over the screen, but here you're

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almost always gonna have more than two choices. This thing

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slides up from the bottom, you're gonna usually have two,

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three, four, five choices, even. And here what you're

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doing is asking the user to make a branching decision.

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Maybe they've asked to take a picture,

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to get a picture in their app, and you wanna know,

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do you want it from the camera or

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do you want it from the photo library, or

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do you want it from somewhere else?

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So they're kind of branching right there and

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you can't really help them until they make that decision

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for you, so that's what an action sheet is for. It's not

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like an alert in that it's for unusual circumstances,

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it's kind of normal branching decisions that you would have

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to make. So here's what these things look like,

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an action sheet slides up from the bottom like that,

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and it can have pretty much any number of buttons although

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obviously, you wouldn't want it to fill the whole screen.

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And then an alert, you've seen those,

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they come up in the middle of the screen,

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they might even have a little text field in them as well.

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So, again, the API for them, i.e, using them,

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the code you write is almost identical, so let's just

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talk about one of them first which is actionSheet. Now,

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the way both of them work, they're just UIViewController.

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There nothing special about them,

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they're just UIViewControllers.

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You know, we learned about how to present a UIViewController

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modally in the last lecture, when we put our emoji art

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controller document up modally,

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it took over the whole screen until we said done.

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Same thing here with alerts and

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action sheets. This UIAlertController is

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a UIViewController and we're just gonna present it using

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exactly the same method we did to present our document.

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It's called present, but we're not gonna create it by getting

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it out the storyboard like what we did with our document.

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We're gonna create it with this initializer,

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UIAlertController title message preferredStyle. And so

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the title is just the title you can see on the left there,

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the image where the title goes, right?

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It's the little thing at the top Redeploy Cassini, and then

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the message goes below that issue commands to Cassini's

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guidance system. And then the preferredStyle is either

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actionSheet or alert. So, this is what it looks like for

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actionSheet. Now, you create your actionSheet and

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then you want to add actions, these actions correspond to

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the buttons. So, we have four actions right there in our

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example in what we're gonna control Cassini here, and so

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we're gonna have four times we're gonna call a addAction.

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The argument to addAction, there's only one argument,

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it's a UIAlertAction. Which is another object and

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let's take a look at the initializer for

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UIAlertAction. It takes a title, that's gonna be

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the title that appears on the button, a style, we'll talk

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about the styles in a moment here, and then a handler, and

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a handler is just a closure you're gonna give it. It takes

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the action as an argument so that it's in your right hand,

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and you're gonna do whatever you do when that button gets

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clicked. So, this alert in action,

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sheets have a very simple API, you just put these buttons and

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the code that goes with them on each one.

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So this handler for, our first button there, Orbit Saturn,

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was just kind of a normal button, so its style is

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UIAlertActionStyle.default. And the handler in there,

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I'm just going to go into orbit around Saturn. And

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that's someone, presumably, pressed this button once,

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and Cassini did that, it's finished now,

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but it did that at one point. So this is just the normal

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default, action here to orbit Saturn, right?

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And I can add another action, maybe Explore Titan, now,

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okay that's not Cassini's mission, but

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maybe we could allow it if we let, make the person logins.

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So in the handler there, I've asked them to log in to verify

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they really want to divert Cassini to Titan, right?

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How about the next one, which is the Closeup of the Sun?

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Well if I really wanted to send, this Cassini off to

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the Sun, that would almost certainly destroy Cassini.

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And that's why it has a little different style there, which

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is .destructive, you see where it says style .destructive? So

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a .destructive item is gonna show up in red text right

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there and it's any choice that is going to make us,

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kind of significant unrecoverable action happen.

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you're gonna delete something out of a database.

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For example,

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That might be a destructive action, obviously crashing

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Cassini into the Sun, that would be a destructive action,

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so that's what .destructive style is there. And

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then, finally, we have this cancel action at the bottom,

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you see it's kinda separated a little?

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And its style is different,

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.cancel, that's what it causes it to be separated. But a very

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important other thing about .cancel is that on the iPad,

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this thing is not gonna slide up from the bottom. It's gonna

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appear in a popover, which we haven't talked about,

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and we're gonna talk all about on Wednesday.

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But a popover is also modal, kinda takes over the screen,

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but it appears in a little window and, in there,

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you can't have a cancel button,

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cuz a popover is cancelled by touching somewhere else.

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A popover comes up, if you wanna cancel it,

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you touch somewhere else so you don't need a cancel,

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you don't wanna cancel button. That's why it's important to

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note which of your buttons are a cancel button, so

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that when this appears in a popover,

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the action sheet here won't include that cancel buttons.

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All right, so we've added our four buttons,

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now we want this thing to slide up to the bottom and

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let the user choose and execute the appropriate

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handler and we do that with that same method,

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present. It's a ViewController method, present,

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presumably the ViewController behind there, you can see that

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it's got the picture of Cassini. That ViewController

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is presenting this action sheet and it's, you know,

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present the view controller, animated true, almost always,

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and then completion handler if you want for which will

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get called when the animation finishes. So that's it,

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super easy to use an alert.

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Now let's talk about, this is an action sheet, by the way.

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So let's talk about what it looks like on iPad, though,

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I said it was a popover, this is is what it would look like.

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In this case, you see that little redeploy button?

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And it's kinda small font, but

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it says redeploy in the upper right of the iPad.

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When I click that, this action sheet presented well,

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first of all how do I get it to present like that?

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And then second of all, how do I get it to point to

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the little redeploy button. So I have to do both of those

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things. The first thing I'm going to do is make it present

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like a popover. And to do that, I set the alerts,

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which is a view control remember, I set

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it's modalPresentationStyle to be .popover. And that's gonna

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make it to represent as a popover. But that's not

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quite enough because I have to make a point at that little

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redeploy bar button item. And the way I do that

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is I get the alerts popover presentation controller,

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which will be nil if you're not presenting it as popover.

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And one of the vars in a popover presentation

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controller is the barButton item that is presenting it.

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You can also specify a rectangle,

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an arbitrary rectangle and

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the little triangle will point at that when it appears.

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You can also specify which direction the little arrow is

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allowed to point, left, right, up or down. And in that way

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you can control the way that this popover presents.

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Does this make sense? Now you're probably saying,

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well I need to put if I'm on iPad then do this around this,

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right? Because obviously on an iPhone I don't want

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this thing to be a popover. But actually, you don't have

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to do that, because this exact same code will still slide up

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from the bottom on an iPhone. Now, why does that happen?

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We've specifically asked for the popover presentation style

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there and we specified the barButton item and all that.

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Well, iOS automatically does what we called adapting

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to the environment its in. Both the trait environment,

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right, compact width and or not, and

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all that stuff we talked about before, but also the platform

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its on to some extent. And so here it notices,

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well I'm on an iPhone, I don't do popovers. Actually,

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you can do popovers on iPhone as we'll talk about, but

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you have to do extraordinary things to do that. So

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in the normal case of events it doesn't do popover,

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so it comes over in it's normal way. So

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if you're doing a popover, and

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you have a universal app that runs on both iPad and iPhone,

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you're gonna put this modal presentation stuff in there.

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All right, so let's talk about alert.

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Same exact constructor, you just say preferred style

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alert, same exact adding actions. And

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here I am adding my cancel button,

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I'm marking it as .cancel plus importing in alert because it

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doesn't hide the cancel button in any case cuz alerts look

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exactly the same on both iPads and iPhones. And then I'm

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gonna add another action here which is my login button.

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Now, my login button is going to use that text field,

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you see that text field? So how the heck did I get a text

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field to appear in the middle of my alert?

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Well, I just said alert.addTextField, and

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the argument to that add text field is a closure

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that passes the text field to you and

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allows you to configure it. This is a password for

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redeploying Cassini off to the Sun, or titan, or

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something. So I want it to have secure text entry, so

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I'm using the text field var, there is secure text entry

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which is part of the text input traits protocol that

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text field implements. And you could do this more than once,

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you can have more than one text field.

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I recommend against that, and I generally recommend against

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using an alert as a login screen. Don't do that for

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your final project.

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If you have a login screen,

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make it a normal part of your UI, don't have it be an alert.

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But anyway, once you get this text field added with this and

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configured, then how do you get the text out when someone

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types the text. Well in your handler of the action for

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login right there, I'm just gonna use the var that's in

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alert called text field, it's an array of all the text

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fields. I only have one so I'm going to get the first one and

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then I'm going to get the text out of it.

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Couldn't be simpler.

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00:11:37,764 --> 00:11:41,766
All right, I almost hesitate to show you the alert with

239
00:11:41,834 --> 00:11:43,968
the text field in there because it makes you say,

240
00:11:44,036 --> 00:11:45,970
that's a great way to get text from the user, but

241
00:11:46,039 --> 00:11:50,107
again alerts are disruptive so don't use them for that.

242
00:11:50,176 --> 00:11:53,111
All right, and I'm gonna present this in exact the same

243
00:11:53,179 --> 00:11:56,948
way I presented the action sheet with the present method,

244
00:11:57,017 --> 00:11:59,817
which presents. Just all present does is it presents

245
00:11:59,885 --> 00:12:03,021
a view controller modaly? And of course this is a modal

246
00:12:03,089 --> 00:12:05,790
because the whole screen is dimmed out, except for

247
00:12:05,859 --> 00:12:10,061
this middle box. All right, and as I said,

248
00:12:10,130 --> 00:12:13,431
on the iPad, alerts look exactly the same.

249
00:12:13,500 --> 00:12:18,402
There's no difference. So that's alerts, so let's put

250
00:12:18,471 --> 00:12:21,305
an alert in EmojiArt, just so we could see this in action.

251
00:12:21,374 --> 00:12:25,844
And here's the alert I'm gonna put in. Right now, EmojiArt,

252
00:12:25,912 --> 00:12:29,214
if you drag any image in to EmojiArt, it will work.

253
00:12:29,282 --> 00:12:31,148
And that's because I have that image fetcher,

254
00:12:31,217 --> 00:12:31,950
remember that and

255
00:12:32,018 --> 00:12:35,086
the image fetcher allows you to specify a back-up image.

256
00:12:35,154 --> 00:12:38,556
And so if I can't get the image from the URL

257
00:12:38,625 --> 00:12:39,924
with the image fetcher, no problem,

258
00:12:39,993 --> 00:12:42,326
I'll use the back-up image and create a one on disk and

259
00:12:42,395 --> 00:12:43,795
use that as the URL.

260
00:12:43,863 --> 00:12:47,765
Well that solution doesn't work too well in iCloud drive.

261
00:12:47,834 --> 00:12:50,969
Because I create an EmojiArt document on my iPad,

262
00:12:51,037 --> 00:12:53,304
I drag in something that I couldn't get it's URL so

263
00:12:53,372 --> 00:12:56,206
I just put the image locally. I put it on iCloud Drive,

264
00:12:56,275 --> 00:12:59,243
I go over to my iPhone, I look at it, I can't see it.

265
00:12:59,312 --> 00:13:02,413
Because it's using the backup image which is on my iPad. So

266
00:13:02,482 --> 00:13:05,983
I'm gonna fix my EmojiArt just to simply not accept

267
00:13:06,052 --> 00:13:09,086
those things. So if you drag in something that I can't get

268
00:13:09,155 --> 00:13:10,555
its image from the URL,

269
00:13:10,623 --> 00:13:13,257
I'm just gonna reject it. Now I could just quietly

270
00:13:13,326 --> 00:13:16,594
reject it. And the user would probably be like, what's going

271
00:13:16,663 --> 00:13:18,829
on? I keep dragging this and it won't take it.

272
00:13:18,898 --> 00:13:20,431
But it'd be much better if I put up an alert and

273
00:13:20,500 --> 00:13:23,668
said, I couldn't get the image from that URL, sorry, okay so

274
00:13:23,736 --> 00:13:26,771
that's what we're gonna do. However, once I got used to

275
00:13:26,840 --> 00:13:30,541
that, then I probably don't want it coming up every time.

276
00:13:30,610 --> 00:13:33,611
Because I do get the feedback when I drag in a bad image,

277
00:13:33,679 --> 00:13:35,079
it just does nothing.

278
00:13:35,148 --> 00:13:37,381
And eventually I'll learn, that one I can't drag in,

279
00:13:37,450 --> 00:13:39,250
I'll have to pick something else. And so

280
00:13:39,318 --> 00:13:41,151
I'm going to have my alert have two buttons.

281
00:13:41,220 --> 00:13:44,822
One is keep warning me about this, and the other one is

282
00:13:44,890 --> 00:13:47,491
stop warning me about this. Those are the only two

283
00:13:47,560 --> 00:13:50,227
buttons on my alert. The alert is otherwise just going to say

284
00:13:50,296 --> 00:13:51,763
I couldn't get the image from that URL.

285
00:13:51,831 --> 00:13:54,699
So that's what we're going to build so let's go do that.

286
00:13:58,170 --> 00:14:00,738
To our emojiArt, here we are. So here's emojiArt,

287
00:14:00,806 --> 00:14:03,441
if you remember, we do all of our image dropping down at

288
00:14:03,509 --> 00:14:07,244
the bottom here in our draft interaction delegates here.

289
00:14:07,313 --> 00:14:08,479
Right here is the imageFetcher,

290
00:14:08,548 --> 00:14:12,383
here's what we dropped when we get the URL, we fetch it with

291
00:14:12,452 --> 00:14:15,586
the imageFetcher. But if we get an image, we use it as

292
00:14:15,654 --> 00:14:18,755
a backup image. So we're not gonna do this anymore,

293
00:14:18,824 --> 00:14:22,393
I'm gonna in fact, stop using the imageFetcher all together.

294
00:14:22,461 --> 00:14:25,329
So I'm just gonna comment that imageFetcher out. Instead

295
00:14:25,398 --> 00:14:28,132
what I'm gonna do is what you did probably in your homework,

296
00:14:28,201 --> 00:14:31,135
hopefully. And what we did last week in, or

297
00:14:31,203 --> 00:14:33,170
the week before, in the ImageViewController,

298
00:14:33,239 --> 00:14:35,740
which I'm just gonna fetch this thing directly.

299
00:14:35,808 --> 00:14:37,608
Now one thing I have to be careful about here is I don't

300
00:14:37,677 --> 00:14:42,312
wanna block the main queue. And this closure, the one that

301
00:14:42,381 --> 00:14:46,751
load objects, plural, that I do on a session. This one

302
00:14:46,820 --> 00:14:50,687
is a convenience method, it calls on the main queue.

303
00:14:50,756 --> 00:14:53,357
So this closure is on the main queue doing this. So I do not

304
00:14:53,426 --> 00:14:56,894
want that, I want to dispatch off of the main queue. So I'm

305
00:14:56,962 --> 00:15:01,765
gonna do DispatchQueue.global queue. I'm gonna get

306
00:15:01,834 --> 00:15:05,803
do userInitiated, because the user did just drop this and

307
00:15:05,872 --> 00:15:08,439
is presumably asking me to go do it right now.

308
00:15:08,507 --> 00:15:11,142
And I'm going to asynchronously perform this

309
00:15:11,210 --> 00:15:15,846
block. And what I'm gonna do in this block is go try and

310
00:15:15,915 --> 00:15:18,949
fetch that image. So I'm gonna say, if I can let the image

311
00:15:19,018 --> 00:15:24,688
data equal trying to ask the data to get the contents

312
00:15:24,757 --> 00:15:28,559
of this URL, but I'm actually gonna use the image URL.

313
00:15:28,628 --> 00:15:32,263
As you learn in your homework, sometimes you gotta massage

314
00:15:32,332 --> 00:15:35,733
that URL a little bit to get the right thing out of there.

315
00:15:35,802 --> 00:15:39,737
And then I'm going to let image = UIImage from that

316
00:15:39,805 --> 00:15:43,841
data, if I can, imageData. And if I was successfully able

317
00:15:43,910 --> 00:15:44,676
to do all of that,

318
00:15:44,744 --> 00:15:46,410
and I'm doing this all in another thread, so

319
00:15:46,478 --> 00:15:50,915
it's nice I'm not blocking the UI. Now I can use this URL

320
00:15:50,984 --> 00:15:52,483
absolutely normally. Of course,

321
00:15:52,552 --> 00:15:56,888
I wanna now dispatch back to the main queue. All right?

322
00:15:56,956 --> 00:16:01,059
Cuz I'm gonna do UI thing, which is I'm gonna say,

323
00:16:01,127 --> 00:16:06,096
self.emojiArtBackgroundImage = [url, image].

324
00:16:06,165 --> 00:16:11,069
I'm also gonna do docself.documentChanged.

325
00:16:13,472 --> 00:16:17,107
This is calling the method that used to be called save.

326
00:16:17,176 --> 00:16:19,676
And then after the last lecture I told you I was going

327
00:16:19,745 --> 00:16:22,446
to use delegation to automatically track changes.

328
00:16:22,515 --> 00:16:23,381
Well this is one of the changes I

329
00:16:23,449 --> 00:16:25,182
have to track. If you change the background image,

330
00:16:25,251 --> 00:16:27,050
I have to let the document know that it has changed.

331
00:16:27,119 --> 00:16:29,520
And we're going to look at document change in a little

332
00:16:29,589 --> 00:16:32,256
bit later demo, today. It's exactly the same as save,

333
00:16:32,325 --> 00:16:34,157
I just renamed it document change. But

334
00:16:34,226 --> 00:16:37,128
we definitely want to do that in here. Now, here's the rub.

335
00:16:37,197 --> 00:16:40,797
Here's the alert magic. If I couldn't do that,

336
00:16:40,866 --> 00:16:43,800
if I was unable to get that image out of there. Now I

337
00:16:43,869 --> 00:16:47,638
wanna put up an alert instead of using that backup image. So

338
00:16:47,707 --> 00:16:52,610
I'm going to say here, self.presentBadURLWarning,

339
00:16:52,679 --> 00:16:56,647
and I'm going to actually pass the url along.

340
00:16:56,716 --> 00:16:58,482
Now why am I passing that url along?

341
00:16:58,550 --> 00:17:01,518
I'm not gonna do this for time reasons, but you know what

342
00:17:01,587 --> 00:17:04,689
would be a really cool thing is someone drags something in,

343
00:17:04,757 --> 00:17:07,258
it puts up the alert. They're like, don't warn me again.

344
00:17:07,326 --> 00:17:10,661
And they say stop. But then they drag another one in and

345
00:17:10,729 --> 00:17:13,864
it doesn't work. Then they try a different one and

346
00:17:13,933 --> 00:17:18,035
it doesn't work. And they're like, it's broken. They've

347
00:17:18,104 --> 00:17:20,838
kind of forgotten that they said stop warning me that.

348
00:17:20,906 --> 00:17:22,940
So somehow you might want that alert to come

349
00:17:23,009 --> 00:17:26,644
back on. At some point, right? And what would be a cool way

350
00:17:26,713 --> 00:17:31,082
to do that? How about if they drag the same url in twice.

351
00:17:31,150 --> 00:17:34,351
Because that's them saying, drag it in. It didn't work.

352
00:17:34,420 --> 00:17:37,355
Why didn't it work? Let me try again. Well if they're trying

353
00:17:37,423 --> 00:17:39,657
again they probably forgot about that alert.

354
00:17:39,725 --> 00:17:41,692
Maybe, maybe not, but it's likely.

355
00:17:41,761 --> 00:17:44,428
So that's the kinda thing you can do in your UI that's

356
00:17:44,497 --> 00:17:47,130
a little tricky, that allows them to turn things like that

357
00:17:47,199 --> 00:17:49,633
back on without having to go to settings somewhere and

358
00:17:49,702 --> 00:17:51,568
turn it on, which is really cumbersome.

359
00:17:51,637 --> 00:17:55,005
It's just kind of using their natural things that they're

360
00:17:55,074 --> 00:17:58,208
doing. In the UI, you can make decisions like this.

361
00:17:58,277 --> 00:17:59,243
So I just kinda want to give you just kind of a classic

362
00:17:59,244 --> 00:18:00,210
Does that make sense?

363
00:18:00,279 --> 00:18:02,880
example of that. So that's why I might pass this URL on,

364
00:18:02,949 --> 00:18:05,716
because I might want to check to see if it's the same URL.

365
00:18:05,785 --> 00:18:08,419
Now I'm not gonna do that today, for time constraints.

366
00:18:08,488 --> 00:18:11,189
But I just wanted to give you the idea you could do that.

367
00:18:11,257 --> 00:18:14,124
All right, so let's do our private func here,

368
00:18:14,193 --> 00:18:16,360
presentBadURLWarning for URL.

369
00:18:18,631 --> 00:18:19,864
And what am I gonna do in here?

370
00:18:19,932 --> 00:18:22,232
I'm gonna create that alert and present it.

371
00:18:22,301 --> 00:18:24,335
That's why we're here, is to learn about alerts.

372
00:18:24,403 --> 00:18:27,504
So creating alert is just creating that view controller.

373
00:18:27,573 --> 00:18:31,909
So let alert = UIAlertController.

374
00:18:31,978 --> 00:18:34,778
Why they didn't call it UIAlertViewController,

375
00:18:34,847 --> 00:18:38,616
I do not know. They did not. So UIAlertController, and

376
00:18:38,685 --> 00:18:41,252
the constructor for it here, we always want this one

377
00:18:41,320 --> 00:18:44,054
down here. You can see this one's that NS coder stuff we

378
00:18:44,123 --> 00:18:47,290
learned about before. This is is kind of an old style thing.

379
00:18:47,359 --> 00:18:51,161
We always want this one right here, that gives us the title,

380
00:18:51,230 --> 00:18:53,697
the message that's gonna go in there.

381
00:18:53,766 --> 00:18:57,468
And the style, whether it's an action sheet or an alert. And

382
00:18:57,537 --> 00:18:59,536
so our title here, what's happening?

383
00:18:59,605 --> 00:19:02,005
Well, they dropped an image. We couldn't get the data.

384
00:19:02,074 --> 00:19:06,944
So I'm gonna call this thing Image Transfer Failed, maybe.

385
00:19:07,013 --> 00:19:12,416
It's actually very important to pick good phraseology here,

386
00:19:12,484 --> 00:19:14,619
cuz you don't wanna freak your user out. My gosh,

387
00:19:14,687 --> 00:19:16,387
what did I do or whatever? You wanna try and

388
00:19:16,455 --> 00:19:18,889
give them something that gives them the authority,

389
00:19:18,958 --> 00:19:21,692
kind of project some authority that this, don't worry,

390
00:19:21,760 --> 00:19:24,662
this happened. I understand it and here's your options.

391
00:19:24,730 --> 00:19:26,497
But not something that's so technical that they're like,

392
00:19:26,566 --> 00:19:30,067
what? Like if we say something like couldn't load from URL.

393
00:19:30,136 --> 00:19:32,803
Okay well users don't even know what URLs are. So

394
00:19:32,871 --> 00:19:34,338
you wouldn't wanna put URL in here.

395
00:19:34,407 --> 00:19:35,906
You see what I'm saying? So

396
00:19:35,974 --> 00:19:38,675
image transfer, when they're dragging presumably they're

397
00:19:38,744 --> 00:19:42,079
trying to transfer that image. You know, it's a good name.

398
00:19:42,148 --> 00:19:45,749
Maybe we might even wanna say, image drop failed, possibly.

399
00:19:45,818 --> 00:19:47,818
You know, this is the kind of thing you user test and

400
00:19:47,886 --> 00:19:49,653
you try and get the right words. Of course,

401
00:19:49,722 --> 00:19:51,889
the other thing here is we wanna localize this.

402
00:19:51,958 --> 00:19:54,792
And I'm gonna talk, hopefully the week after Thanksgiving,

403
00:19:54,861 --> 00:19:57,461
about how to localize your app for other languages. Because

404
00:19:57,530 --> 00:20:00,163
we want our app to run in as many languages as possible, so

405
00:20:00,232 --> 00:20:02,866
we have to make that string be able to be localizable.

406
00:20:02,935 --> 00:20:05,903
And it's quite easy to do in iOS, but we'll learn about

407
00:20:05,971 --> 00:20:08,639
that in a couple weeks. And now here's the message where

408
00:20:08,707 --> 00:20:10,540
I'm gonna tell them more about what happened.

409
00:20:10,609 --> 00:20:15,078
So here I'm kind of saying what happened here, which is

410
00:20:15,147 --> 00:20:20,350
that I couldn't transfer the dropped image from its source.

411
00:20:20,419 --> 00:20:22,086
Again, I'm not mentioning the term URL or

412
00:20:22,154 --> 00:20:25,356
anything like that. I'm just doing that. And

413
00:20:25,425 --> 00:20:27,824
of course this is an alert, not an action sheet, so

414
00:20:27,893 --> 00:20:30,995
we'll say that. So this creates this view controller,

415
00:20:31,063 --> 00:20:35,499
and then I'm just going to present I am a view controller

416
00:20:35,568 --> 00:20:39,870
here, present. So I can call this method on myself,

417
00:20:39,939 --> 00:20:41,839
it's a view controller method, present.

418
00:20:41,908 --> 00:20:45,075
I'm gonna present the alert, animated true, and

419
00:20:45,144 --> 00:20:48,678
I don't have any completion thing I wanna do so I'll just

420
00:20:48,747 --> 00:20:52,783
leave that off. But of course I need to add my buttons here.

421
00:20:52,851 --> 00:20:53,784
So what buttons are we gonna have?

422
00:20:53,853 --> 00:20:57,020
Well, remember I'm gonna have keep warning me and stop

423
00:20:57,089 --> 00:21:00,257
warning me. Okay so, let's do the keep warning one first.

424
00:21:00,326 --> 00:21:03,226
So I'm just gonna say alert.addAction and

425
00:21:03,295 --> 00:21:06,897
remember the action you can see takes us one argument,

426
00:21:06,966 --> 00:21:10,635
which is a UIAlertAction. And that has only one initializer,

427
00:21:10,703 --> 00:21:13,370
which is these one right here. So make it so

428
00:21:13,439 --> 00:21:18,509
you can see even better here. All right,

429
00:21:18,578 --> 00:21:21,778
so it wants the title. That's the title of the button. So

430
00:21:21,847 --> 00:21:25,649
this is the one where I'm going to keep warning

431
00:21:25,718 --> 00:21:29,720
the person. And the style for this is just default,

432
00:21:29,789 --> 00:21:32,890
this is the normal default button. Keep Warning isn't

433
00:21:32,958 --> 00:21:34,891
anything special, it's not gonna change anything, really.

434
00:21:34,960 --> 00:21:36,193
We just keep on warning them.

435
00:21:36,262 --> 00:21:37,961
And I actually don't need a handler here,

436
00:21:38,030 --> 00:21:39,296
cuz I'm not gonna do anything,

437
00:21:39,364 --> 00:21:40,764
if you keep saying Keep Warning me,

438
00:21:40,833 --> 00:21:42,132
cuz that's what I do by default.

439
00:21:42,201 --> 00:21:47,438
So I'm just gonna get rid of that, and that's my action. So

440
00:21:47,507 --> 00:21:50,941
a lot of time cancel buttons and okay buttons,

441
00:21:51,009 --> 00:21:53,010
they don't have any action, they don't do anything. And

442
00:21:53,078 --> 00:21:55,645
that's, this is kind of like an okay button in a way. But

443
00:21:55,714 --> 00:22:01,519
our other button alert add action, UIAlertAction.

444
00:22:01,587 --> 00:22:03,888
This one does have a handler, and

445
00:22:03,956 --> 00:22:07,958
let's talk about how we're going to implement this.

446
00:22:11,063 --> 00:22:14,231
Let's see, now it's on one page there. So here this, this

447
00:22:14,300 --> 00:22:17,968
string is Stop Warning. Now if I just have Stop Warning and

448
00:22:18,037 --> 00:22:21,038
Keep Warning, that's really not enough information for

449
00:22:21,106 --> 00:22:22,272
people to understand.

450
00:22:22,341 --> 00:22:25,409
What do you mean Stop Warning? You know what I mean? So

451
00:22:25,478 --> 00:22:28,079
I actually wanna add a little more to my message up here.

452
00:22:28,147 --> 00:22:32,916
I'm gonna say something along the lines of,

453
00:22:32,985 --> 00:22:36,487
show this warning in the future?

454
00:22:36,555 --> 00:22:40,024
Now, Keep Warning and Stop Warning make a lot more sense.

455
00:22:41,227 --> 00:22:44,528
However, you don't want this to be yes and

456
00:22:44,596 --> 00:22:47,698
no. Having buttons in an alert, yes and no.

457
00:22:47,767 --> 00:22:50,567
That forces the person to go carefully read and

458
00:22:50,636 --> 00:22:53,971
parse the message you said. And they don't get any double

459
00:22:54,040 --> 00:22:56,473
check that they read it right before they press yes or no.

460
00:22:56,542 --> 00:23:00,176
So always try to pick things that are more descriptive than

461
00:23:00,245 --> 00:23:03,747
yes or no, like keep this warning, stop this warning.

462
00:23:03,816 --> 00:23:05,215
Okay you still have to be brief,

463
00:23:05,284 --> 00:23:07,751
you don't want these buttons to have ten words on them.

464
00:23:07,820 --> 00:23:09,553
So it's a compromise between brevity and

465
00:23:09,621 --> 00:23:11,054
making sure the person understands.

466
00:23:11,123 --> 00:23:14,391
Now I'm gonna call this destructive because it's going

467
00:23:14,459 --> 00:23:17,294
to stop it doing something that it does pretty much

468
00:23:17,363 --> 00:23:19,963
permanently unless I go add that feature where

469
00:23:20,032 --> 00:23:23,400
I compare the URLs and turn it back on. So I'm gonna set this

470
00:23:23,469 --> 00:23:25,970
to destructive. So it's gonna turn out red. It's gonna

471
00:23:26,038 --> 00:23:28,339
make the user think a little bit before they press that,

472
00:23:28,407 --> 00:23:31,609
which is exactly what I want. And how about our handler

473
00:23:31,677 --> 00:23:35,446
here. So the handler passes this action back to us. And

474
00:23:35,514 --> 00:23:38,448
we usually don't need that because

475
00:23:38,517 --> 00:23:42,018
we can just capture it in using closure capture,

476
00:23:42,087 --> 00:23:47,224
we capture this little action. Although, you know, since you

477
00:23:47,293 --> 00:23:49,893
usually add it like this, you don't actually have a local

478
00:23:49,962 --> 00:23:52,328
var to this action. So it's kinda nice that it passes it.

479
00:23:52,397 --> 00:23:55,166
We don't need it in any case. All we need to do here is set

480
00:23:55,234 --> 00:23:57,801
some var that says, suppress these warnings.

481
00:23:57,870 --> 00:24:03,173
So I'm gonna say self. suppressBadURLWarnings = true,

482
00:24:03,242 --> 00:24:08,011
so I need a var for this. So I'll put that up here,

483
00:24:08,080 --> 00:24:12,149
private var, I think I copy and pasted it, yeah I did.

484
00:24:12,217 --> 00:24:14,118
Equals, of course it's gonna start out false,

485
00:24:14,187 --> 00:24:15,385
we're not gonna suppress it.

486
00:24:15,454 --> 00:24:22,226
And all I'm gonna do is, not do this method if that's true,

487
00:24:22,294 --> 00:24:27,564
so I'm gonna say if suppressBadURLWarnings,

488
00:24:27,633 --> 00:24:33,103
not then do this. So

489
00:24:33,172 --> 00:24:36,239
that's it, that's the entire implementation of this,

490
00:24:36,308 --> 00:24:42,946
let's go see this working. Here's our app right here,

491
00:24:43,014 --> 00:24:46,717
let's open up our Apple Bees document right here. Here it

492
00:24:46,785 --> 00:24:50,887
is, and let's try dragging in an image, that works.

493
00:24:50,956 --> 00:24:53,423
How about I think this one works, this one has an URL.

494
00:24:53,492 --> 00:24:56,860
So we drag it in, it loads it up, excellent, it worked,

495
00:24:56,929 --> 00:24:59,863
it's got a high resolution image, that's good.

496
00:24:59,932 --> 00:25:01,865
How about let's drag in one that doesn't work,

497
00:25:01,934 --> 00:25:05,168
how about this one? This one happens to not have a good

498
00:25:05,237 --> 00:25:08,071
URL, all right, we got an alert here.

499
00:25:08,140 --> 00:25:11,074
Couldn't transfer the dropped image from the source,

500
00:25:11,143 --> 00:25:14,044
show this warning in the future, keep the warning, or

501
00:25:14,112 --> 00:25:17,581
stop warning, so I will keep warning. That's good,

502
00:25:17,650 --> 00:25:21,251
let's try another one, how about this one down here?

503
00:25:21,320 --> 00:25:24,355
That's also no good, now I'm tired of this warning, so

504
00:25:24,423 --> 00:25:28,458
I'm gonna say, stop warning me. Now let's try and

505
00:25:28,527 --> 00:25:32,162
drag this bad one in again right here,

506
00:25:32,231 --> 00:25:36,333
no warning. All right, so that's that,

507
00:25:36,401 --> 00:25:38,869
let's get back to our slides, and

508
00:25:38,938 --> 00:25:42,072
action sheet is exactly the same, right?

509
00:25:42,140 --> 00:25:45,843
You're gonna do exactly the same thing over there.

510
00:25:45,911 --> 00:25:51,515
All right, our next topic here is notifications and KVO.

511
00:25:51,583 --> 00:25:55,152
So if you remember back to the MVC talk I did at the very

512
00:25:55,220 --> 00:25:58,055
beginning, like, second lecture. I had this little

513
00:25:58,124 --> 00:26:00,657
radio station, the little orange things right there.

514
00:26:00,726 --> 00:26:04,862
I said, well, the model can't talk to its controller, so it

515
00:26:04,930 --> 00:26:07,531
has to use other mechanisms. And why can't the model talk

516
00:26:07,600 --> 00:26:11,402
to the controller? Because the model is UI independent and

517
00:26:11,470 --> 00:26:13,570
the component is fundamentally UI dependent.

518
00:26:13,639 --> 00:26:16,005
So there's no way for them to talk in that direction.

519
00:26:16,074 --> 00:26:18,541
The controller can talk to the model, but not the other way,

520
00:26:18,610 --> 00:26:21,378
so we have this blind and structured way of doing it.

521
00:26:21,447 --> 00:26:24,248
By the way, a view might also want to use this

522
00:26:24,316 --> 00:26:26,850
radio station to talk to its controller because the view

523
00:26:26,919 --> 00:26:28,618
can't also talk to its controller for

524
00:26:28,687 --> 00:26:32,322
a different reason. The view is generic, and the controller

525
00:26:32,391 --> 00:26:35,725
is specific UI. So there's no way generic items like

526
00:26:35,794 --> 00:26:38,661
buttons could know anything about a particular controller.

527
00:26:38,730 --> 00:26:41,631
So for both reasons, the viewing model ca't talk to

528
00:26:41,700 --> 00:26:44,334
the controller, controller talking to them is okay, but

529
00:26:44,403 --> 00:26:45,369
ca't do the other way. So

530
00:26:45,437 --> 00:26:48,005
they both could use this radio station model. And there's

531
00:26:48,073 --> 00:26:50,974
really two ways to do radio stations, notifications and

532
00:26:51,043 --> 00:26:54,144
KVO, KVO stands for key value observing.

533
00:26:54,212 --> 00:26:57,213
So we're gonna talk about this radio station, by the way,

534
00:26:57,282 --> 00:26:59,983
only I call it radio station, it's not called radio station

535
00:27:00,052 --> 00:27:02,586
in the doc. But a radio station is a good analogy for

536
00:27:02,654 --> 00:27:05,789
the kind of communication that's going on between these

537
00:27:05,858 --> 00:27:10,661
things. All right, here's notifications, the first of

538
00:27:10,729 --> 00:27:13,931
these. So a notification is essentially just

539
00:27:13,999 --> 00:27:17,667
a way you're gonna register a closure to get called when

540
00:27:17,736 --> 00:27:22,072
someone broadcasts on a named radio station. That's all it

541
00:27:22,140 --> 00:27:25,509
is, very simple, you can see how it's immediately blind.

542
00:27:25,578 --> 00:27:27,377
Nobody knows who's any classes,

543
00:27:27,446 --> 00:27:31,681
all we're talking about here is this radio station. And

544
00:27:31,750 --> 00:27:32,449
it's very flexible,

545
00:27:32,518 --> 00:27:35,318
cuz you just plop a closure down there, and it just calls

546
00:27:35,387 --> 00:27:37,854
it when someone broadcasts on that radio station. And

547
00:27:37,923 --> 00:27:41,659
it's also possible to broadcast music on a radio

548
00:27:41,727 --> 00:27:44,461
station. In other words, when you broadcast,

549
00:27:44,529 --> 00:27:47,630
you can put information across the radio station as well,

550
00:27:47,699 --> 00:27:48,798
which is kinda cool.

551
00:27:48,867 --> 00:27:51,901
All right, so this is what the function to say I wanna

552
00:27:51,970 --> 00:27:54,471
listen to a radio station looks like, this

553
00:27:54,540 --> 00:27:59,543
code you see up right here. All of this stuff is done via

554
00:27:59,611 --> 00:28:03,447
this thing right here, NotificationCenter.default.

555
00:28:03,516 --> 00:28:05,181
You see that NotificationCenter.default,

556
00:28:05,250 --> 00:28:08,285
and I'm using it down here. So NotificationCenter is a thing

557
00:28:08,354 --> 00:28:10,988
that you use to both sign up to listen to a radio station,

558
00:28:11,057 --> 00:28:13,456
and to broadcast on a radio station. And

559
00:28:13,525 --> 00:28:16,960
we always just use this default shared instance of it,

560
00:28:17,028 --> 00:28:19,162
kind of like user default, remember that one?

561
00:28:19,230 --> 00:28:22,565
We had userdefault.standard, we just used the shared one,

562
00:28:22,634 --> 00:28:24,734
same thing here. So

563
00:28:24,803 --> 00:28:28,138
this method to say you wanna listen is called addObserver.

564
00:28:28,206 --> 00:28:31,608
You're essentially going to observe this radio station,

565
00:28:31,677 --> 00:28:34,244
to listen to see if anything is broadcast

566
00:28:34,312 --> 00:28:37,080
there. And you see it has a return value there, which is

567
00:28:37,149 --> 00:28:40,851
of type NSObjectProtocol, I'm gonna cover that in a second.

568
00:28:40,920 --> 00:28:43,653
But first let's look at the arguments to this thing.

569
00:28:43,722 --> 00:28:46,656
First of all, we have forName, you see this, right, forName,

570
00:28:46,725 --> 00:28:50,293
Notification.Name, that's the name of the radio station. And

571
00:28:50,362 --> 00:28:52,629
notice it's type is not string,

572
00:28:52,697 --> 00:28:56,733
it's Notification.Name. And so if you, when you name it,

573
00:28:56,801 --> 00:28:59,402
you will have to create your own Notification.Name if you

574
00:28:59,471 --> 00:29:02,105
wanna broadcast on your own radio station. Which is fine,

575
00:29:02,174 --> 00:29:05,142
you wanna give your radio station a unique name. But

576
00:29:05,210 --> 00:29:08,278
if you wanna look and find the radio stations that exist

577
00:29:08,347 --> 00:29:12,315
already in iOS, and there are dozens of them. iOS is very

578
00:29:12,384 --> 00:29:14,618
good at broadcasting on a lot of radio stations.

579
00:29:14,687 --> 00:29:16,153
You can just go look in the documentation for

580
00:29:16,221 --> 00:29:18,721
Notification.Name, and you'll see them all listed there.

581
00:29:18,790 --> 00:29:22,358
What they do, when they broadcast, that kind of stuff.

582
00:29:22,427 --> 00:29:24,661
So that's why it's nice that they made it not a string,

583
00:29:24,729 --> 00:29:27,664
but a type that you can go look up in the documentation.

584
00:29:27,733 --> 00:29:30,700
All right, the next thing is this object Any?.

585
00:29:30,769 --> 00:29:33,570
That is who's broadcasting on this radio station,

586
00:29:33,639 --> 00:29:35,739
because unlike real radio stations,

587
00:29:35,808 --> 00:29:39,242
multiple people can broadcast on the same frequency,

588
00:29:39,311 --> 00:29:42,178
and that's perfectly allowed. And this just says who

589
00:29:42,247 --> 00:29:45,716
is broadcasting at the, who did the broadcast that you're

590
00:29:45,784 --> 00:29:49,386
receiving when your closure gets called here. And

591
00:29:49,454 --> 00:29:51,254
then you see right there, we have the queue,

592
00:29:51,322 --> 00:29:54,391
this OperationQueue. That's what queue do you want your

593
00:29:54,460 --> 00:29:58,462
closure to be executed on. Now, this can be nil, but

594
00:29:58,530 --> 00:30:01,365
you almost never want nil. What nil means is,

595
00:30:01,433 --> 00:30:07,804
execute my closure on the same queue as the broadcaster.

596
00:30:07,873 --> 00:30:11,041
You do not want that usually, unless you're the broadcaster,

597
00:30:11,109 --> 00:30:12,976
if it's your own code, and you're doing the broadcasting,

598
00:30:13,045 --> 00:30:14,411
maybe you want that. But

599
00:30:14,480 --> 00:30:15,979
if you're listening to something from iOS, for

600
00:30:16,048 --> 00:30:18,548
example, no, you probably want the main queue. Now,

601
00:30:18,616 --> 00:30:22,318
notice that says operation queue, not dispatch queue, and

602
00:30:22,387 --> 00:30:24,521
I actually mentioned this when I talked about dispatch queue.

603
00:30:24,590 --> 00:30:27,857
That there's an object oriented API to doing all that

604
00:30:27,926 --> 00:30:31,061
dispatch stuff, called Operation and OperationQueue.

605
00:30:31,129 --> 00:30:33,363
Well, this is using that object-oriented API,

606
00:30:33,432 --> 00:30:34,431
if you want the main queue,

607
00:30:34,500 --> 00:30:36,667
which is what you want 99% of the time,

608
00:30:36,735 --> 00:30:39,336
just say OperationQueue.main. The same way you say

609
00:30:39,404 --> 00:30:43,239
DispatchQueue.main, you can say OperationQueue.main. And

610
00:30:43,308 --> 00:30:46,576
then the last argument to this addObserver is the closure you

611
00:30:46,644 --> 00:30:49,046
want to execute. And that closure only has one argument,

612
00:30:49,114 --> 00:30:52,548
which is a notification. A notification is just a little

613
00:30:52,617 --> 00:30:55,786
object that has, for example, the name of the radio station

614
00:30:55,854 --> 00:30:58,488
and who the broadcaster is. But it also has a very

615
00:30:58,557 --> 00:31:01,224
important piece of information called userInfo.

616
00:31:01,293 --> 00:31:05,162
userInfo is the music that's being broadcast to you,

617
00:31:06,298 --> 00:31:07,163
it's almost always,

618
00:31:07,232 --> 00:31:10,567
it's a type any, but it's almost always a dictionary.

619
00:31:10,635 --> 00:31:13,136
And when you look in the documentation notification

620
00:31:13,205 --> 00:31:14,871
name to find all the radio stations.

621
00:31:14,940 --> 00:31:17,507
They will say, when we broadcast,

622
00:31:17,576 --> 00:31:21,110
we include the following keys in the dictionary, this

623
00:31:21,179 --> 00:31:25,815
information. So that's a very important piece to understand,

624
00:31:25,884 --> 00:31:28,418
is that your closure has this one argument, notification.

625
00:31:28,486 --> 00:31:31,287
You look at the var userInfo in that notification to get

626
00:31:31,356 --> 00:31:34,858
the music that's coming across the radio station right now,

627
00:31:34,926 --> 00:31:37,160
all right? Now let's talk about that return value,

628
00:31:37,229 --> 00:31:38,761
you see that observer up there?

629
00:31:38,830 --> 00:31:41,832
Notice that really weird type, NSObjectProtocol,

630
00:31:41,900 --> 00:31:44,600
what the heck is NSObjectProtocol?

631
00:31:44,669 --> 00:31:47,470
NSObjectProtocol is a protocol that NSObject happens to

632
00:31:47,539 --> 00:31:51,074
implement. It's a subset of the functionality of NSObject

633
00:31:51,143 --> 00:31:54,811
that some objects implement that aren't subclasses of

634
00:31:54,880 --> 00:31:58,314
NSObject. So that, you know, this kind, this well-known

635
00:31:58,383 --> 00:32:01,985
set of things. However, that's completely irrelevant here.

636
00:32:02,054 --> 00:32:05,188
Does not matter. That thing might as well be in any as far

637
00:32:05,257 --> 00:32:08,191
as you're concerned. All this thing, this observer thing is

638
00:32:08,259 --> 00:32:12,395
a cookie that just keeps track, that basically this

639
00:32:12,464 --> 00:32:15,431
observation is this thing. So, it's just a cookie for

640
00:32:15,500 --> 00:32:18,668
you to hold on to. You only do one thing with it,

641
00:32:18,737 --> 00:32:22,038
which is stop observing. It's how you say

642
00:32:22,107 --> 00:32:25,242
I don't wanna listen to that radio station anymore. And

643
00:32:25,310 --> 00:32:28,678
you do that by asking the NotificationCenter.default to

644
00:32:28,747 --> 00:32:32,415
remove observer, this cookie. And it will stop listening. So

645
00:32:32,484 --> 00:32:35,384
we'll show you an example of that in a second.

646
00:32:35,453 --> 00:32:39,923
Quickly on Notification.Name, all of the notification names,

647
00:32:39,992 --> 00:32:43,459
they collect them as static lets, little static let

648
00:32:43,528 --> 00:32:48,131
constant Notification.Names in the Notification.Name class.

649
00:32:48,200 --> 00:32:51,735
By the way, you'll often see it called NSNotification.Name.

650
00:32:51,803 --> 00:32:52,802
That's the same thing.

651
00:32:52,871 --> 00:32:55,771
They're literally type aliased to each other. You know,

652
00:32:55,840 --> 00:32:57,941
in the Swift world, we would call it Notification.Name,

653
00:32:58,009 --> 00:33:00,810
and in the Objective-C world, NSNotification.Name.

654
00:33:00,879 --> 00:33:04,581
Fine, they're the same exact thing. And again, if you wanna

655
00:33:04,650 --> 00:33:08,151
create your own radio station, we actually, or I recommend

656
00:33:08,220 --> 00:33:11,254
creating an extension to Notification.Name, and

657
00:33:11,323 --> 00:33:14,590
adding your own static let which is your thing, equals,

658
00:33:14,659 --> 00:33:19,295
Notification.Name, of some string, any string you want.

659
00:33:19,364 --> 00:33:21,898
That way you'll be collected in exactly the same

660
00:33:21,967 --> 00:33:25,101
kind of API realm as all of the other notification names.

661
00:33:25,170 --> 00:33:28,338
And you'll see that when we do the demo. All right, so

662
00:33:28,407 --> 00:33:31,675
here's an example of listening to the radio station.

663
00:33:31,743 --> 00:33:32,609
What's a good example?

664
00:33:32,677 --> 00:33:34,410
This is a great example. Remember,

665
00:33:34,479 --> 00:33:37,080
the slider that said, set your font size, the accessibility

666
00:33:37,148 --> 00:33:40,283
slider? You can make it bigger and smaller? Well, you can

667
00:33:40,352 --> 00:33:43,786
find out, because there's a radio station broadcast

668
00:33:43,855 --> 00:33:47,257
anytime that changes. So that's a great thing to know.

669
00:33:47,325 --> 00:33:50,260
If you have something in your UI whose font is based on

670
00:33:50,329 --> 00:33:53,697
that, for example, we talked about doing the cool thing of

671
00:33:53,765 --> 00:33:56,632
having the collection view on the top of emoji art,

672
00:33:56,701 --> 00:34:00,704
having its emoji get bigger or smaller, based on this slider.

673
00:34:00,772 --> 00:34:02,472
Which would not be that hard to do. I'm not

674
00:34:02,540 --> 00:34:05,308
gonna do it as a demo but you can do it as an exercise.

675
00:34:05,376 --> 00:34:09,079
The main thing we would have to do is have our cell size

676
00:34:09,148 --> 00:34:13,950
be, fixed to this font size by doing our

677
00:34:14,019 --> 00:34:16,886
little font metric scaling. And we would also have to have

678
00:34:16,955 --> 00:34:20,123
a layout constraint for the height of our collection view

679
00:34:20,191 --> 00:34:23,159
that we wanna set in code to be the height of the cells.

680
00:34:23,227 --> 00:34:26,062
Because remember that our cells can't be larger than our

681
00:34:26,131 --> 00:34:28,698
collection view. So we'd have to make the collection view

682
00:34:28,766 --> 00:34:31,168
bigger and the cells. But we could easily do that.

683
00:34:31,236 --> 00:34:33,102
But if we did that, we would definitely want to be

684
00:34:33,171 --> 00:34:34,537
listening to this radio station.

685
00:34:34,606 --> 00:34:36,772
Because every time that font changed,

686
00:34:36,841 --> 00:34:40,143
we'd have to re-layout our collection view, of course,

687
00:34:40,211 --> 00:34:42,278
all right? So here's what it would look like.

688
00:34:42,347 --> 00:34:44,781
We get the NotificationCenter.default.

689
00:34:44,849 --> 00:34:47,884
We create this observer var which we set equal to doing

690
00:34:47,953 --> 00:34:51,121
addObserver. The name of that radio station is

691
00:34:51,189 --> 00:34:55,758
Notification.Name.UIContentSi- zeCategoryDidChange.

692
00:34:55,827 --> 00:34:57,861
That's kind of a mouthful but that's what it is.

693
00:34:57,929 --> 00:35:01,197
We're listening for that from UIApplication.shared.

694
00:35:01,266 --> 00:35:03,432
That's the application object. I'm gonna talk about that at

695
00:35:03,501 --> 00:35:06,636
the end of this lecture. You could also put nil there.

696
00:35:06,705 --> 00:35:09,305
Cuz basically if anyone broadcasts that thing changed,

697
00:35:09,374 --> 00:35:12,408
you're interested. So it would be fine to say nil here.

698
00:35:12,477 --> 00:35:14,977
That means if anybody broadcasts it. And then of

699
00:35:15,046 --> 00:35:18,548
course OperationQueue.main. I say or nil but really we would

700
00:35:18,617 --> 00:35:21,484
want .main there. Cuz we're not actually sure what thread

701
00:35:21,553 --> 00:35:23,720
this iOS would be broadcasting this on.

702
00:35:23,788 --> 00:35:26,323
So we want to make sure we're on the main thread when we

703
00:35:26,391 --> 00:35:30,160
do our stuff, and then our closure. Now inside our

704
00:35:30,229 --> 00:35:33,196
closure we cause our collection view to redraw.

705
00:35:33,265 --> 00:35:36,766
Whatever we do is fine. And also notice there,

706
00:35:36,834 --> 00:35:39,135
there's something, some music broadcast on this station.

707
00:35:39,204 --> 00:35:43,439
Which is, you can find out the content size category. And so

708
00:35:43,508 --> 00:35:45,775
there's names for all those detentes,

709
00:35:45,844 --> 00:35:50,213
in the slider there, like UIContentSizeCategorySmall,

710
00:35:50,281 --> 00:35:54,517
UIContentSizeLarge, UIContentSizeCategoryAccessib-

711
00:35:54,585 --> 00:35:56,452
ilityLarge, which is even larger.

712
00:35:56,521 --> 00:35:58,521
And there's like very large, and extra large, I don't know.

713
00:35:58,590 --> 00:36:01,690
There's all kinds of different spots in there that you could

714
00:36:01,759 --> 00:36:04,026
look at if you wanted to. But you're probably not going to.

715
00:36:04,095 --> 00:36:06,596
You're probably in that collection example just going

716
00:36:06,665 --> 00:36:08,731
to resize your font based on the font metrics.

717
00:36:08,800 --> 00:36:11,434
Remember how we do that scaled font thing off the UI Metrics.

718
00:36:11,502 --> 00:36:15,605
You would just cause that to recalculate, all right? Now,

719
00:36:15,674 --> 00:36:19,375
notice that I hold on to var observer right there. And then

720
00:36:19,444 --> 00:36:22,979
I remove it when I'm done. So, it is a good question here.

721
00:36:23,048 --> 00:36:27,316
When do I add and when do I remove observing. Well, almost

722
00:36:27,385 --> 00:36:29,886
always you're doing this as part of something you're doing

723
00:36:29,954 --> 00:36:32,822
in the ViewController. So a perfect time and

724
00:36:32,890 --> 00:36:36,392
probably 90% of the time, when you get viewWillAppear or

725
00:36:36,461 --> 00:36:39,529
viewDidAppear, you add observer. And

726
00:36:39,598 --> 00:36:42,398
then on viewWillDisappear or viewDidDisappear,

727
00:36:42,467 --> 00:36:45,635
you remove the observer. That makes sense?

728
00:36:45,704 --> 00:36:48,504
Because you're only interested in really getting these size

729
00:36:48,573 --> 00:36:51,441
changes while you're on-screen.

730
00:36:51,509 --> 00:36:52,675
of course, the size might change while you're offscreen.

731
00:36:52,676 --> 00:36:53,842
Now if you do that,

732
00:36:53,912 --> 00:36:55,311
So when you get viewWillAppear,

733
00:36:55,380 --> 00:36:57,780
you'll probably also wanna look at the size category,

734
00:36:57,849 --> 00:36:59,782
which you can do. UIApplication has a var for

735
00:36:59,851 --> 00:37:02,418
that. And adjust your collection view then

736
00:37:02,487 --> 00:37:05,221
before you appear. But it's kinda a waste for you to

737
00:37:05,290 --> 00:37:08,091
be listening to that thing all the time and changing things

738
00:37:08,159 --> 00:37:10,359
when you're not even on screen. So viewWillAppear,

739
00:37:10,428 --> 00:37:13,429
viewDidDisappear are great places to put add observer,

740
00:37:13,498 --> 00:37:16,765
remove observer pairs. Always pair these things. Don't

741
00:37:16,834 --> 00:37:22,605
forget to remove observer. How about broadcasting on your own

742
00:37:22,674 --> 00:37:25,508
radio station. How do you do that? You do that with

743
00:37:25,577 --> 00:37:27,577
the NotificationCenter.default as well.

744
00:37:27,646 --> 00:37:30,680
The method there is called post. The first argument,

745
00:37:30,748 --> 00:37:32,715
the name, is the name of the radio station.

746
00:37:32,784 --> 00:37:35,585
You get to make that up. We've talked about how to do that.

747
00:37:35,654 --> 00:37:38,755
object, that's you. That's who's sending it. Usually

748
00:37:38,823 --> 00:37:40,890
that's self. You can make that any object that you want.

749
00:37:40,958 --> 00:37:43,393
But, that is who the NotificationCenter will

750
00:37:43,461 --> 00:37:44,627
report as the sender,

751
00:37:44,696 --> 00:37:48,197
the broadcaster. And then userInfo, that's

752
00:37:48,266 --> 00:37:51,034
your music. And that's, almost always, you're gonna want to

753
00:37:51,102 --> 00:37:53,502
put that as a dictionary of AnyHashable thing

754
00:37:53,571 --> 00:37:56,639
to an Anys. So it's very flexible, you can put anything

755
00:37:56,707 --> 00:38:00,510
you want in there. Now, as soon as you call this method,

756
00:38:00,578 --> 00:38:04,648
it will immediately call all the closures for

757
00:38:04,716 --> 00:38:07,683
that have addObserver to your radio station,

758
00:38:07,752 --> 00:38:12,388
with a following caveat. It's only gonna immediately

759
00:38:12,457 --> 00:38:15,357
call them If they specified queue nil.

760
00:38:15,426 --> 00:38:17,960
Cuz then it's gonna execute their closures on the same

761
00:38:18,029 --> 00:38:21,130
queue as this. So then it executes right away.

762
00:38:21,198 --> 00:38:23,800
If they specified a different queue like the main queue,

763
00:38:23,869 --> 00:38:27,069
then this is going to post their closures to execute.

764
00:38:27,138 --> 00:38:29,405
And it will execute as soon as that

765
00:38:29,474 --> 00:38:33,175
queue gets around to their closure.

766
00:38:33,244 --> 00:38:37,079
So that's notifications. All right, KVO. Now I'm gonna

767
00:38:37,148 --> 00:38:39,949
spend two slides on this. But I wanna emphasize up front,

768
00:38:40,018 --> 00:38:43,452
this is not a major important thing you're gonna do this.

769
00:38:43,521 --> 00:38:46,656
Most quarters, I don't even talk about this. But

770
00:38:46,724 --> 00:38:49,024
I kinda decided to throw it in this quarter just so

771
00:38:49,093 --> 00:38:51,928
you can kinda know it exists out there.

772
00:38:51,997 --> 00:38:54,630
It's not really a primary way of doing things.

773
00:38:54,699 --> 00:38:57,032
Notification is much more of a primary way.

774
00:38:57,101 --> 00:39:00,136
This much less primary. And it's because, it's because

775
00:39:00,205 --> 00:39:03,506
it's kinda limited a little bit in its application.

776
00:39:03,575 --> 00:39:07,576
So what is KVO? The basic idea here is, when it comes right

777
00:39:07,645 --> 00:39:12,048
down to it, it's the idea of registering a closure that

778
00:39:12,116 --> 00:39:16,619
gets executed when a property on a sub-class of NSObject

779
00:39:16,688 --> 00:39:19,822
changes. That's pretty much what it is.

780
00:39:19,891 --> 00:39:23,826
Now let's talk about some of the caveats I just put there.

781
00:39:23,895 --> 00:39:27,096
To make KVO work, you can't just have any property and

782
00:39:27,164 --> 00:39:30,099
you change it and someone can register a closure.

783
00:39:30,168 --> 00:39:32,369
Think about the overhead of doing that.

784
00:39:32,437 --> 00:39:33,903
You would not want that for every property.

785
00:39:33,972 --> 00:39:36,706
A lot of properties are probably they act as inlined

786
00:39:36,774 --> 00:39:37,440
by the compiler.

787
00:39:37,508 --> 00:39:40,309
So there's no way you would be able to do that. So

788
00:39:40,378 --> 00:39:42,612
there's a mechanism that's required to do this.

789
00:39:42,681 --> 00:39:45,414
Now NSObject, remember what NSObject is, right?

790
00:39:45,483 --> 00:39:48,051
It's the root of all iOS classes, right? So

791
00:39:48,119 --> 00:39:51,721
UIViewController, UIView, they all inherit from NSObject.

792
00:39:51,790 --> 00:39:54,290
So NSObject puts this mechanism

793
00:39:54,359 --> 00:39:57,193
that makes it possibly to watch a property into it.

794
00:39:57,261 --> 00:40:00,930
So that's why I say This is for subclasses of NSObject,

795
00:40:00,998 --> 00:40:03,666
you could put this mechanism in your own object, however.

796
00:40:03,735 --> 00:40:06,402
It's not that difficult, I'm not gonna cover it, but

797
00:40:06,471 --> 00:40:09,372
people usually don't. They just use the mechanism of

798
00:40:09,441 --> 00:40:12,808
using NSObject by having their thing, whatever it is,

799
00:40:12,877 --> 00:40:15,745
their class, subclass from NSObject. So

800
00:40:15,814 --> 00:40:17,580
that's the first thing to understand.

801
00:40:17,648 --> 00:40:19,716
There's kind of some mechanism there that you would have

802
00:40:19,784 --> 00:40:21,851
to implement if you didn't wanna subclass NSObject.

803
00:40:23,321 --> 00:40:26,255
What is this thing good for, what's KVO good for? Well,

804
00:40:26,324 --> 00:40:28,724
it's kind of good for some the same things as notification.

805
00:40:28,793 --> 00:40:31,427
Blind structured communication between things,

806
00:40:31,496 --> 00:40:34,196
especially between models and their controllers.

807
00:40:34,265 --> 00:40:36,365
But also between a view and their controller, or

808
00:40:36,434 --> 00:40:38,534
even between a view and itself, as you'll see in

809
00:40:38,603 --> 00:40:42,739
the demo here. Not every property works with KVO,

810
00:40:42,808 --> 00:40:44,607
as I said, that would be ridiculous. For

811
00:40:44,676 --> 00:40:46,008
a property to work with it,

812
00:40:46,077 --> 00:40:48,077
not only do you need the NSObject mechanism, but

813
00:40:48,146 --> 00:40:51,480
the property has to be what's called key value coding

814
00:40:51,549 --> 00:40:53,516
compliant. Now, what that means is,

815
00:40:53,585 --> 00:40:56,853
that property can be set by sending set value for

816
00:40:56,921 --> 00:41:00,723
key, where the key is the key path of that property, and

817
00:41:00,791 --> 00:41:02,892
get value for key to get it. In other words,

818
00:41:02,960 --> 00:41:05,895
there's these functions, set value for key and value for

819
00:41:05,963 --> 00:41:08,831
key, that you can call to get the value of the property.

820
00:41:08,900 --> 00:41:11,367
That has to be possible on the object,

821
00:41:11,436 --> 00:41:13,903
that has to work if you want do it. And

822
00:41:13,972 --> 00:41:16,872
that's called key value compoding, key value coding

823
00:41:16,941 --> 00:41:19,842
compliant. So that property has to be that way, now,

824
00:41:19,910 --> 00:41:23,646
you have to do some work to make that happen. Properties

825
00:41:23,714 --> 00:41:26,182
don't just magically make that work, you usually have to

826
00:41:26,250 --> 00:41:28,717
implement something like value for key and set value for

827
00:41:28,786 --> 00:41:31,887
key to make that work. Now, there are a few properties

828
00:41:31,956 --> 00:41:36,559
scattered throughout iOS that are key value observing,

829
00:41:36,628 --> 00:41:38,861
that work with key value observing. Most notably,

830
00:41:38,930 --> 00:41:42,965
in UI view, center and frame are key value observing.

831
00:41:43,033 --> 00:41:46,235
So you can observe the center or frame, and/or frame of

832
00:41:46,304 --> 00:41:48,338
a view, and you can find out when it moves, so

833
00:41:48,406 --> 00:41:52,007
that's kinda cool. Also, most of the properties in

834
00:41:52,076 --> 00:41:55,077
the CALayer underneath UIView, remember the place where we

835
00:41:55,146 --> 00:41:56,545
put the border around the view,

836
00:41:56,614 --> 00:41:58,648
back in assignment three or something like that?

837
00:41:58,716 --> 00:42:02,618
That layer that's doing a lot of the drawing for UIView,

838
00:42:02,687 --> 00:42:06,722
that layer is mostly key value observing compliant. So you

839
00:42:06,791 --> 00:42:09,392
can observe things happening at that layer as well. And

840
00:42:09,461 --> 00:42:11,393
they are scattering other places, for example,

841
00:42:11,462 --> 00:42:15,398
core data. Remember core data, the object oriented database?

842
00:42:15,466 --> 00:42:17,933
Key value observing can be really big there.

843
00:42:18,002 --> 00:42:21,304
You could watch everything happening in your database

844
00:42:21,372 --> 00:42:25,307
on a per-property basis by using key value observing. So

845
00:42:25,376 --> 00:42:29,078
there are some frameworks that actually use KVO a lot. But

846
00:42:29,147 --> 00:42:32,014
for the most part, we don't use it in the main

847
00:42:32,083 --> 00:42:34,684
line that much. And of course, you could make your own

848
00:42:34,752 --> 00:42:36,886
NSObject subclass that implements this stuff.

849
00:42:36,954 --> 00:42:39,354
But that's way outside the scope of this class, and

850
00:42:39,423 --> 00:42:42,258
again, template sizing is not, this is not that huge a deal.

851
00:42:42,326 --> 00:42:45,394
All right, so how does that work, what is KVO look like?

852
00:42:45,463 --> 00:42:48,497
There's this one very important method that NSObject

853
00:42:48,566 --> 00:42:51,134
provides for you, called observe. So

854
00:42:51,202 --> 00:42:54,570
observe takes a keyPath as an argument and a closure, and

855
00:42:54,639 --> 00:42:58,240
it executes that closure whenever that keyPath changes.

856
00:42:58,309 --> 00:43:01,477
Only works for keyPath that are key value compliant,

857
00:43:01,545 --> 00:43:05,214
key value coding compliant. Notice that it returns

858
00:43:05,283 --> 00:43:07,683
a little cookie, our observation,

859
00:43:07,752 --> 00:43:09,918
you see that? It's a little different than a notification,

860
00:43:09,987 --> 00:43:13,956
though, you never say, remove observer on that cookie.

861
00:43:14,025 --> 00:43:17,159
Instead, when that cookie goes out of the heap,

862
00:43:17,228 --> 00:43:20,262
it stops observing. So as long as you want this

863
00:43:20,331 --> 00:43:23,265
observation closure to be observing that thing,

864
00:43:23,334 --> 00:43:25,935
just keep that cookie in the heap. As soon as you let it go

865
00:43:26,003 --> 00:43:30,339
out of the heap, it will stop observing. Now,

866
00:43:30,408 --> 00:43:32,574
the arguments you see to your closure, of course,

867
00:43:32,643 --> 00:43:35,377
you get the thing that's being observed, observed handed back

868
00:43:35,446 --> 00:43:37,313
to you. You also get this thing change,

869
00:43:37,382 --> 00:43:41,617
that change is of type NSKeyValueObservedChange. And

870
00:43:41,685 --> 00:43:44,954
that's a little object that you can get the old value of

871
00:43:45,022 --> 00:43:47,089
the thing, the new value of the thing that changed,

872
00:43:47,158 --> 00:43:49,691
that kind of stuff. It just basically tells you about

873
00:43:49,760 --> 00:43:51,059
the change that happened,

874
00:43:51,128 --> 00:43:53,328
that caused your closure to get called.

875
00:43:53,397 --> 00:43:57,199
This KeyPath argument is not a string, used to be in the old

876
00:43:57,268 --> 00:44:01,003
days. Nowadays, it's actually a typed thing in Swift, and

877
00:44:01,071 --> 00:44:04,806
it has special syntax, which is backslash, the type, dot,

878
00:44:04,875 --> 00:44:09,645
the name of the property. Now, Swift will infer the type for

879
00:44:09,714 --> 00:44:13,749
you, so we almost always say backslash dot the property. So

880
00:44:13,818 --> 00:44:15,918
for example, if we want to observe the center or

881
00:44:15,987 --> 00:44:21,523
frame of a view we would say observe \.frame.

882
00:44:21,592 --> 00:44:26,295
and that will be observing the view's frame. All right,

883
00:44:26,364 --> 00:44:28,530
so I have a demo of both of these things,

884
00:44:28,599 --> 00:44:31,934
notifications and KVO, so let's take a look at these.

885
00:44:32,003 --> 00:44:35,571
What I'm gonna do here is, remember after last lecture,

886
00:44:35,639 --> 00:44:39,342
I said, we don't want to have a save button in EmojiArt.

887
00:44:39,411 --> 00:44:40,209
We're gonna get rid of that,

888
00:44:40,278 --> 00:44:42,144
there's no reason to have a save button. Really,

889
00:44:42,212 --> 00:44:45,080
when we hit Save, we were just telling our UI document,

890
00:44:45,149 --> 00:44:48,951
something changed, so you should autosave soon.

891
00:44:49,019 --> 00:44:51,854
Really, what we want is to watch our EmojiArt view,

892
00:44:51,923 --> 00:44:54,490
and whenever an emoji gets added or resized or

893
00:44:54,559 --> 00:44:57,126
moved, we want to notify the controller.

894
00:44:57,195 --> 00:44:59,628
So the controller can tell its document, something changed,

895
00:44:59,697 --> 00:45:01,530
then we can just ditch the save button.

896
00:45:01,599 --> 00:45:03,232
Well, after lecture last time,

897
00:45:03,301 --> 00:45:05,267
I told you I was gonna do that, and I did.

898
00:45:05,336 --> 00:45:09,004
So the stuff that's posted has this in there, and what I used

899
00:45:09,073 --> 00:45:12,208
was delegation. And it did it specifically cuz I wanted you

900
00:45:12,277 --> 00:45:14,910
to see what it looks like to make your own delegate.

901
00:45:14,979 --> 00:45:16,779
You've been using scroll view's delegate,

902
00:45:16,847 --> 00:45:19,448
table view's delegate, collective view's delegate.

903
00:45:19,517 --> 00:45:22,585
I wanted you to see, wanted you to make your own delegate,

904
00:45:22,654 --> 00:45:25,354
so I created an EmojiArtViewDelegate, and

905
00:45:25,423 --> 00:45:27,556
I'll briefly show you what I did there.

906
00:45:27,625 --> 00:45:31,293
And so that's great, but today, what I'm gonna do is

907
00:45:31,362 --> 00:45:34,663
use notifications instead. Because you can image,

908
00:45:34,732 --> 00:45:36,332
anything that's happening with a delegate,

909
00:45:36,401 --> 00:45:38,634
that's blind structure communication. Well, we can do

910
00:45:38,702 --> 00:45:40,937
that with a notification just by having a radio station,

911
00:45:41,005 --> 00:45:44,039
which is the EmojiArt view something changed radio

912
00:45:44,108 --> 00:45:47,076
station. And a controller will just tune in, and every time

913
00:45:47,145 --> 00:45:49,878
it hears a broadcast on that, it'll tell its UI document,

914
00:45:49,947 --> 00:45:53,015
something changed, that's what I heard on the radio station.

915
00:45:53,084 --> 00:45:55,751
And so that's what we'll do there, and then KVO,

916
00:45:55,820 --> 00:45:57,552
there's a great use of KVO here.

917
00:45:57,621 --> 00:46:00,456
Which is, right now, I had to go down where my gestures are,

918
00:46:00,524 --> 00:46:03,125
remember, I dragged in some gesture code. I had to go in

919
00:46:03,193 --> 00:46:05,894
there, and for every time a gesture changed the position

920
00:46:05,963 --> 00:46:08,697
of an emoji, I had to tell my delegate something changed,

921
00:46:08,766 --> 00:46:11,433
tell me. So I had a lot of code in there for that, so

922
00:46:11,502 --> 00:46:13,569
I'm just gonna rip all that code out.

923
00:46:13,638 --> 00:46:16,606
And instead, I'm gonna observe the center of my emojis, and

924
00:46:16,674 --> 00:46:19,241
when my emojis move, or even when they're resized,

925
00:46:19,309 --> 00:46:22,077
because when they resize, they have to be repositioned,

926
00:46:22,146 --> 00:46:24,546
right? Cuz they grow from the upper left corner,

927
00:46:24,615 --> 00:46:26,248
so I have to keep repositioning, so

928
00:46:26,317 --> 00:46:28,251
I'm setting the center again. So

929
00:46:28,319 --> 00:46:30,786
I'm just gonna observe that, and when that happens,

930
00:46:30,855 --> 00:46:33,255
then I'll broadcast on my radio station. So

931
00:46:33,324 --> 00:46:36,392
that'll collect that code into one place, and keep it from

932
00:46:36,460 --> 00:46:40,729
being spread out through all over my code in a messy way.

933
00:46:40,798 --> 00:46:43,832
But before we do that stuff, I'm going to do a simple

934
00:46:43,901 --> 00:46:47,202
notification thing, which is I'm just going to observe

935
00:46:47,271 --> 00:46:50,839
the state of my UI document changing. You know how our UI

936
00:46:50,908 --> 00:46:53,976
document goes through these document states, normal,

937
00:46:54,045 --> 00:46:57,580
closed, progress available when it's, say, reading and

938
00:46:57,648 --> 00:47:00,749
writing, saving, error, remember all those states?

939
00:47:00,818 --> 00:47:03,552
Well, we're gonna watch that happen, just to kinda get

940
00:47:03,621 --> 00:47:07,690
a warm up on notifications, to see what that looks like. So

941
00:47:07,759 --> 00:47:10,158
let's do that one, I'm gonna go up here,

942
00:47:10,227 --> 00:47:13,729
here's viewWillAppear, right here, and close. Right, so

943
00:47:13,798 --> 00:47:16,632
here's our document opening and closing up here. So

944
00:47:16,700 --> 00:47:22,070
all I'm gonna do here is, when my document first appears,

945
00:47:22,139 --> 00:47:26,342
I'm going to start watching my document. And it broadcasts on

946
00:47:26,411 --> 00:47:29,779
a radio station that tells me when its state changed.

947
00:47:29,847 --> 00:47:31,547
So what does that look like, well,

948
00:47:31,616 --> 00:47:33,849
again, i need to capture the return values.

949
00:47:33,918 --> 00:47:36,985
So, i'm gonna call my documentObserver equals,

950
00:47:37,054 --> 00:47:39,856
let's go ahead and make a var for that.

951
00:47:39,924 --> 00:47:43,659
private var documentObserver, remember, it's

952
00:47:43,727 --> 00:47:47,863
an NSObjectProtocol, optional. Again, this is the cookie,

953
00:47:47,932 --> 00:47:50,432
we never send a message to this, ever. We don't

954
00:47:50,501 --> 00:47:54,369
even not know what messages it responds to. So we're gonna,

955
00:47:54,438 --> 00:47:57,839
create this document observer here, I'm gonna do

956
00:47:57,908 --> 00:48:01,743
NotificationCenter.default That's how we do all of our

957
00:48:01,812 --> 00:48:06,382
stuff. And do addObserver, so here's addObserver forName,

958
00:48:06,450 --> 00:48:08,817
make this a little easier to read,

959
00:48:08,886 --> 00:48:14,123
is what I want to do here. I wish they had

960
00:48:14,192 --> 00:48:17,726
a little command key I could do that would do this for me.

961
00:48:17,795 --> 00:48:21,263
All right, so we're gonna listen to the document state

962
00:48:21,332 --> 00:48:23,799
radio station. So we, let's find the name of it.

963
00:48:23,867 --> 00:48:27,002
I'm just gonna type, Notification.Name., and

964
00:48:27,071 --> 00:48:30,839
you're gonna see how many radio stations there are in

965
00:48:30,908 --> 00:48:36,512
iOS. A lot, okay? And you can go look at all these and

966
00:48:36,581 --> 00:48:39,115
what they broadcast and what music they play and all these

967
00:48:39,183 --> 00:48:41,484
things. We've already talked about some of these things,

968
00:48:41,552 --> 00:48:45,954
for example, keyboard. Here's a keyboard hide, DidHide,

969
00:48:46,023 --> 00:48:50,793
will show. And then of course the content category size did

970
00:48:50,862 --> 00:48:54,096
change thing, right? There's that there.

971
00:48:54,165 --> 00:48:58,901
So, the one we want is UIDocumentStateChanged,

972
00:48:58,970 --> 00:49:02,338
you see the first one there? So UIDocumentStateChanged, so

973
00:49:02,407 --> 00:49:04,139
that's the radio station we want to listen to.

974
00:49:04,208 --> 00:49:07,710
We're only interested in broadcast from our document.

975
00:49:09,113 --> 00:49:11,247
That's the sender. That's who we want to broadcast.

976
00:49:11,315 --> 00:49:16,218
We of course want to be on the main queue here. And

977
00:49:16,286 --> 00:49:19,154
here's the closure that's gonna be executed when someone

978
00:49:19,223 --> 00:49:21,690
broadcasts on that. Here's our notification. Now

979
00:49:21,759 --> 00:49:24,259
this notification I think it actually does have some music

980
00:49:24,328 --> 00:49:26,895
on there, which is probably the document state. But

981
00:49:26,964 --> 00:49:29,031
I don't even need it cuz I've got my document right here.

982
00:49:29,100 --> 00:49:32,534
So I'll just grab its state. I'm just gonna say

983
00:49:32,603 --> 00:49:37,940
print.documentState changed to. And

984
00:49:38,008 --> 00:49:45,414
we'll say are self.documentState. I actually

985
00:49:45,482 --> 00:49:48,617
added a little extension to documentState right there so

986
00:49:48,686 --> 00:49:51,553
that it would print it out nicely .normal.close,

987
00:49:51,622 --> 00:49:54,222
those kind of things. Now anytime you start listening

988
00:49:54,291 --> 00:49:56,826
on a radio station, you immediately have to think when

989
00:49:56,894 --> 00:49:59,094
am I going to stop listening on this radio station?

990
00:49:59,163 --> 00:50:02,297
Well, here I'm starting even before my document opens, but

991
00:50:02,366 --> 00:50:05,800
I'm waiting until view will appear. So I'm going to stop,

992
00:50:05,869 --> 00:50:07,903
I could stop in view will disappear or

993
00:50:07,972 --> 00:50:08,770
view did disappear, but

994
00:50:08,839 --> 00:50:10,672
I'm actually going to stop when my document is fully

995
00:50:10,741 --> 00:50:12,374
closed. Once it's fully closed,

996
00:50:12,443 --> 00:50:15,277
I certainly don't want to be watching it anymore. So

997
00:50:15,346 --> 00:50:18,313
let's go down here where we close. This is the close,

998
00:50:18,382 --> 00:50:20,949
here is where we closing. Right now we don't use

999
00:50:21,018 --> 00:50:25,387
the little success closure that happens when we close.

1000
00:50:25,455 --> 00:50:30,326
But I'm going to star using it. Success in space,

1001
00:50:30,394 --> 00:50:35,397
Return. And in here I'm going to remove observing

1002
00:50:35,466 --> 00:50:39,435
this documentObserver. So I'm just going to say here,

1003
00:50:39,503 --> 00:50:44,406
if I can let observer, server equal my documentObserver.

1004
00:50:44,475 --> 00:50:48,710
Then I'm going to ask the NotificationCenter.default

1005
00:50:48,779 --> 00:50:51,213
center to remove that observer.

1006
00:50:51,281 --> 00:50:57,085
In other words, stop observing that. Everybody cool

1007
00:50:57,154 --> 00:51:00,755
with that? Everyone understand what I'm saying here, about

1008
00:51:00,824 --> 00:51:05,393
this is the completion closer from closing the document? So

1009
00:51:05,462 --> 00:51:07,897
once it's closed, that way we'll be able to observe it

1010
00:51:07,965 --> 00:51:13,736
closing. It will be nice. So let's go run this and

1011
00:51:13,804 --> 00:51:16,438
watch our console, so I got my console going down here.

1012
00:51:16,507 --> 00:51:20,209
Actually, this is my console over here. All right, so

1013
00:51:20,278 --> 00:51:26,581
let's run. All right, so here's our app. So we

1014
00:51:26,650 --> 00:51:28,684
haven't opened any documents. So we have nothing on here.

1015
00:51:28,752 --> 00:51:32,621
I'm gonna go ahead and clear out my console.

1016
00:51:32,689 --> 00:51:34,022
So we haven't opened any documents.

1017
00:51:34,091 --> 00:51:35,724
So we haven't gotten any documents to exchange.

1018
00:51:35,792 --> 00:51:38,860
So I'm gonna open our Apple Bees. Here is our Apple Bee.

1019
00:51:38,929 --> 00:51:42,230
And look, documentState date changed to normal, right?

1020
00:51:42,299 --> 00:51:43,565
Because we opened the document,

1021
00:51:43,634 --> 00:51:47,102
now it's in normal. Now, how about putting something in

1022
00:51:47,171 --> 00:51:50,539
here maybe an apple, something like that. Now it's, where,

1023
00:51:50,608 --> 00:51:53,809
what's going to happen to the state right now? Okay well,

1024
00:51:53,878 --> 00:51:56,211
eventually it's going to autosave. It does it about,

1025
00:51:56,280 --> 00:51:58,580
I don't know, once a minute or something like that. But

1026
00:51:58,649 --> 00:52:01,082
when it autosaves, we're going to notice because it's going

1027
00:52:01,151 --> 00:52:04,787
to go to state progress available. There it is,

1028
00:52:04,855 --> 00:52:07,489
progress available and then back to normal. Because

1029
00:52:07,557 --> 00:52:09,358
the progress is available because it's saving and

1030
00:52:09,426 --> 00:52:12,327
it can tell you the progress as it saves, and

1031
00:52:12,396 --> 00:52:16,031
then goes back to normal. I'll show you another trick. Here,

1032
00:52:16,100 --> 00:52:20,869
you can force an autosave, by the way, by threatening

1033
00:52:20,937 --> 00:52:24,707
to switch to another app. Watch this, I'm going to drag

1034
00:52:24,775 --> 00:52:27,175
up from the bottom like, I'm gonna switch to another app.

1035
00:52:27,244 --> 00:52:30,512
This caused an autosave. Now, it didn't do it here because

1036
00:52:30,581 --> 00:52:32,514
we haven't made any changes. But this is a great way

1037
00:52:32,583 --> 00:52:35,150
to make sure that you're changing stuff works.

1038
00:52:35,218 --> 00:52:38,787
So watch this, now I'm gonna add a something here.

1039
00:52:38,856 --> 00:52:42,257
Now when I do this threat, whoop,

1040
00:52:42,326 --> 00:52:46,828
it's saved. See what happened there? So when you threaten to

1041
00:52:46,897 --> 00:52:48,797
switch to another app autosave will auto save.

1042
00:52:48,866 --> 00:52:51,033
Cuz it's just afraid, my gosh, I might get killed or

1043
00:52:51,101 --> 00:52:53,101
who knows what, I better save. So

1044
00:52:53,170 --> 00:52:56,605
that's a nice trick to know when to do that. And

1045
00:52:56,673 --> 00:53:01,310
if we close this then we get state changed to closed. So

1046
00:53:01,379 --> 00:53:03,012
this is cool. We just listened to that radio station,

1047
00:53:03,080 --> 00:53:04,913
we're just reporting what happened.

1048
00:53:04,982 --> 00:53:07,649
All right, now let's go ahead and

1049
00:53:07,718 --> 00:53:10,952
have our emoji artview be a broadcaster.

1050
00:53:11,021 --> 00:53:15,257
We are listening to UIDocument which is the broadcaster here

1051
00:53:15,326 --> 00:53:17,993
and we are the subscriber to the radio station.

1052
00:53:18,062 --> 00:53:19,728
Now let's go the other way, let's have a broadcast.

1053
00:53:19,797 --> 00:53:22,698
So I'm gonna go over to EmojiArt, and what I'm gonna

1054
00:53:22,766 --> 00:53:25,133
do is every where I was doing my delegation,

1055
00:53:25,202 --> 00:53:28,570
I'm going to use notification instead. So let's first review

1056
00:53:28,639 --> 00:53:32,274
what I did after last lecture to implement delegation.

1057
00:53:32,343 --> 00:53:36,378
All right, now, just like UIScrollView, UITableView,

1058
00:53:36,446 --> 00:53:39,848
etc, I had to add a protocol for delegation.

1059
00:53:39,917 --> 00:53:41,683
Now my delegation protocol it's called

1060
00:53:41,752 --> 00:53:45,487
EmojiArtViewDelegate only has one function in it which is

1061
00:53:45,556 --> 00:53:48,256
emojiArtViewChanged. Of course ScrollView has a whole bunch

1062
00:53:48,325 --> 00:53:51,326
of them. DidScroll, view for zooming at, table views

1063
00:53:51,395 --> 00:53:54,897
delegate has a lot of things. Height of row at, all these

1064
00:53:54,965 --> 00:53:58,199
other things. We only have one, just this one. Now notice

1065
00:53:58,268 --> 00:54:02,370
I made this restricted to only being implemented by classes.

1066
00:54:02,439 --> 00:54:06,374
Why did I do that? Because the delegate method, or var,

1067
00:54:06,443 --> 00:54:11,013
the delegate var in my view, I wanted it to be weak. And for

1068
00:54:11,081 --> 00:54:13,748
it to be weak, it has to be able to be in the heap,

1069
00:54:13,817 --> 00:54:15,317
and then get released and

1070
00:54:15,386 --> 00:54:18,720
set to nil, when no one else is interested in it. Why did I

1071
00:54:18,789 --> 00:54:22,557
make that weak? Well, imagine here that my controller sets

1072
00:54:22,626 --> 00:54:26,361
itself as the delegate, which is likely. Very, very likely.

1073
00:54:26,430 --> 00:54:29,765
If that happened, now we'd have a memory cycle

1074
00:54:29,834 --> 00:54:32,100
because my view would be pointing to the controller.

1075
00:54:32,168 --> 00:54:34,702
And of course, the controller points to all of its view.

1076
00:54:34,771 --> 00:54:36,204
So now they are pointing to each other.

1077
00:54:36,273 --> 00:54:38,006
They are going to keep each other in the heap.

1078
00:54:38,075 --> 00:54:40,208
By making this delegate weak, it makes so

1079
00:54:40,277 --> 00:54:43,578
that's no longer going to happen.

1080
00:54:43,647 --> 00:54:45,914
So there's not a memory cycle because the view is not

1081
00:54:45,983 --> 00:54:48,817
keeping the controller in memory cuz this is a weak

1082
00:54:48,886 --> 00:54:52,254
pointer to it. So I added this var, this weak var, so

1083
00:54:52,323 --> 00:54:54,789
now anybody who wants to know if I've changed can just set

1084
00:54:54,858 --> 00:54:56,958
themselves as the delegate and of course the controller is

1085
00:54:57,027 --> 00:55:02,730
going to do that. Then, every time I changed like right down

1086
00:55:02,799 --> 00:55:07,102
here. I just sent this message to my delegate if I have one.

1087
00:55:07,171 --> 00:55:09,905
My delegate could be nil, I don't have to have a delegate.

1088
00:55:09,973 --> 00:55:10,672
And I just send it and

1089
00:55:10,741 --> 00:55:13,575
of course I'm the sender, right? Delegate methods, we

1090
00:55:13,644 --> 00:55:16,444
all will send ourselves along as the first argument. Do you

1091
00:55:16,513 --> 00:55:18,179
know? You've noticed that I'm sure with ScrollView and

1092
00:55:18,248 --> 00:55:20,415
TabelView and collection. They always send themselves,

1093
00:55:20,484 --> 00:55:24,319
it's just convenience sake so that you have it right there.

1094
00:55:24,388 --> 00:55:26,788
So I do that as well. Now this is not the only change,

1095
00:55:26,857 --> 00:55:29,390
this is one I'm dropping. Of course, if I drop a new

1096
00:55:29,459 --> 00:55:32,694
emoji in, that's a change, but I also had to go over here to

1097
00:55:32,763 --> 00:55:34,730
gestures. And this is what I was talking about before,

1098
00:55:34,798 --> 00:55:35,731
it's kind of annoying

1099
00:55:35,799 --> 00:55:39,033
like when I select and move a view. I had to say, well,

1100
00:55:39,102 --> 00:55:42,137
if this is the end of this gesture then send it.

1101
00:55:42,205 --> 00:55:45,274
And also down here where I resized. I had to go and say,

1102
00:55:45,342 --> 00:55:47,009
well, if it's the end of resizing, send it.

1103
00:55:47,077 --> 00:55:48,577
Now I want to get rid of these and

1104
00:55:48,645 --> 00:55:51,179
I'm going to be able to with KVO, but we'll leave them in

1105
00:55:51,248 --> 00:55:55,551
there for now. So that's delegation. That's all that's

1106
00:55:55,619 --> 00:55:58,754
necessary on this view side. Then on the controller side,

1107
00:55:58,822 --> 00:56:02,891
what I did was when I created my emojiArtView down here,

1108
00:56:02,960 --> 00:56:05,627
I set myself as its delegate.

1109
00:56:05,695 --> 00:56:07,729
Well, if I'm gonna be its delegate,

1110
00:56:07,798 --> 00:56:11,166
that means I have to implement the EmojiArtViewDelegate just

1111
00:56:11,235 --> 00:56:13,968
like those implementing scrollviews delegate.

1112
00:56:14,037 --> 00:56:16,638
And that means I have to actually implement that which

1113
00:56:16,707 --> 00:56:19,174
is right here in my emojiArtViewDelegate methods

1114
00:56:19,243 --> 00:56:22,844
implemented, and what did I do? I called documentChanged,

1115
00:56:22,912 --> 00:56:26,815
and what is document changed? Here is document changed,

1116
00:56:26,884 --> 00:56:30,118
it's the method formerly known as Save.

1117
00:56:30,187 --> 00:56:32,621
Cuz I ditched my Save button when I did this and

1118
00:56:32,689 --> 00:56:35,324
just called and Save. These contents up here is exactly

1119
00:56:35,392 --> 00:56:37,492
the same as it used to be. Just update my documents

1120
00:56:37,561 --> 00:56:39,994
model to be my model and then update the documents changed

1121
00:56:40,063 --> 00:56:43,298
count. It's all I do here. So that's delegation,

1122
00:56:43,367 --> 00:56:45,467
that's the entirety of it. You see how it all works?

1123
00:56:45,535 --> 00:56:47,769
Quite simple, and we're not gonna,

1124
00:56:47,838 --> 00:56:50,706
we're not use delegation anymore in this.

1125
00:56:50,774 --> 00:56:52,674
We're gonna leave delegation in the view but

1126
00:56:52,743 --> 00:56:54,576
we're not gonna use it in our controller.

1127
00:56:54,645 --> 00:56:55,844
Instead, we're gonna use a radio station.

1128
00:56:55,912 --> 00:56:57,779
So let's go back to our artview and

1129
00:56:57,848 --> 00:57:00,315
broadcast on a radio station. And I'm just gonna do

1130
00:57:00,383 --> 00:57:02,250
it everywhere where I was talking to my delegate.

1131
00:57:02,319 --> 00:57:04,652
Instead, I'm gonna broadcast on a radio station.

1132
00:57:04,721 --> 00:57:08,223
I'm just gonna say NotificationCenter.default.p-

1133
00:57:08,292 --> 00:57:10,358
ost, that's how we broadcast.

1134
00:57:10,427 --> 00:57:14,395
And I have to give it a name and who is broadcasting. Well,

1135
00:57:14,464 --> 00:57:17,232
who is broadcasting is me, and what are we gonna do for

1136
00:57:17,300 --> 00:57:22,304
a name? Well, as I suggested, I recommend going here and

1137
00:57:22,372 --> 00:57:26,641
doing an extension to notification.name and

1138
00:57:26,710 --> 00:57:31,613
add your own static let which I'll call EmojiArtView

1139
00:57:31,681 --> 00:57:35,617
did change notification and set it equal to

1140
00:57:35,686 --> 00:57:40,856
a notification.name with any string you want in here.

1141
00:57:40,924 --> 00:57:42,824
I'll probably just use the same string here.

1142
00:57:42,893 --> 00:57:45,460
It doesn't have to be the same string but I will, and

1143
00:57:45,529 --> 00:57:46,628
this will now make it so

1144
00:57:46,697 --> 00:57:48,964
you can do notification.name.emojiartvie-

1145
00:57:49,032 --> 00:57:51,967
wdidchange. That's the name of our radio station.

1146
00:57:52,035 --> 00:57:55,003
Remember radio stations are Notification.Names, so

1147
00:57:55,071 --> 00:57:59,107
this is that. So now, I can go down here and

1148
00:57:59,176 --> 00:58:05,947
say I want my name to be Notification.Name.EmojiArtVie-

1149
00:58:06,016 --> 00:58:12,253
wDidChange. And by the way, of course, Swift can infer this.

1150
00:58:12,322 --> 00:58:15,056
So we can just go like that, which is what we would do, and

1151
00:58:15,125 --> 00:58:17,459
type all of that in Notification.Name stuff for

1152
00:58:17,527 --> 00:58:20,328
no good reason. And this is it, so that's all we need to

1153
00:58:20,397 --> 00:58:22,864
do is do this. Now of course, we need to do it here,

1154
00:58:22,933 --> 00:58:25,333
but we have to go again over to gestures over here.

1155
00:58:25,402 --> 00:58:29,204
And do it in the same place we do this delegate right here,,

1156
00:58:29,273 --> 00:58:31,406
where's this other one up here?

1157
00:58:31,475 --> 00:58:33,341
Okay so, again, that's kind of annoying,

1158
00:58:33,410 --> 00:58:35,844
we'll fix that with KVO. But right now, we're broadcasting

1159
00:58:35,913 --> 00:58:37,846
on this radio station every time something changes.

1160
00:58:37,915 --> 00:58:40,415
We resize something, we drop something, and whatever.

1161
00:58:40,484 --> 00:58:42,583
Now, back over here in our controller,

1162
00:58:42,652 --> 00:58:44,619
I'm no longer going to be a delegate.

1163
00:58:44,687 --> 00:58:47,255
So I'm gonna go down here and just get rid of all this.

1164
00:58:47,323 --> 00:58:50,492
So I'm not longer gonna set myself as the delegate here.

1165
00:58:50,560 --> 00:58:54,496
Get rid of this entirely, I'm no longer gonna implement

1166
00:58:54,565 --> 00:58:58,566
the EmojiArtView delegate. I'm no longer going to say that

1167
00:58:58,635 --> 00:59:01,202
I implement the EmojiartView delegate.

1168
00:59:01,271 --> 00:59:04,072
So, now I've disconnected myself from my view.

1169
00:59:04,141 --> 00:59:06,942
So instead, I'm gonna listen to that radio station, so

1170
00:59:07,010 --> 00:59:10,212
where am I gonna do that? That one, let's start listening

1171
00:59:10,280 --> 00:59:13,548
once the document's open. Until the document's open it's

1172
00:59:13,616 --> 00:59:16,651
gonna be useless to listen to my emojiArtview. So again,

1173
00:59:16,720 --> 00:59:20,054
I'm gonna need another little observer guy here.

1174
00:59:20,123 --> 00:59:23,491
So I'm gonna call this one my emojiArtviewObserver cuz

1175
00:59:23,560 --> 00:59:27,062
that's what its gonna be observing, the emojiArtview.

1176
00:59:27,131 --> 00:59:30,332
I'm gonna say emojiArtViewObserver, go,

1177
00:59:30,401 --> 00:59:35,369
'm inside a closure here, cuz this is the completion closure

1178
00:59:35,438 --> 00:59:40,943
of opening. So I'm gonna say self.emojiArtViewObserver

1179
00:59:41,011 --> 00:59:45,280
= NotificationCenter, that's how we listen.

1180
00:59:45,349 --> 00:59:50,218
Default.addObserver, same way as we add observer for

1181
00:59:50,287 --> 00:59:55,157
the UIDocumentState. Let's sort this out again,

1182
00:59:55,225 --> 00:59:59,761
so we can see this all real clearly. All right, so

1183
00:59:59,830 --> 01:00:05,300
the name is notification.Name.EmojiArtVie-

1184
01:00:05,369 --> 01:00:09,937
wDidChange. And again, we don't need that just I was

1185
01:00:10,006 --> 01:00:13,107
doing that so we would see it clearly. The object is my

1186
01:00:13,176 --> 01:00:17,612
EmojiArtView, that's the only one I'm interested in hearing

1187
01:00:17,681 --> 01:00:20,815
about emojiArt, you did change broadcast.

1188
01:00:20,884 --> 01:00:25,620
The Queue, of course operation Queue.Mean because I'm just,

1189
01:00:25,688 --> 01:00:29,858
although surprisingly this would not need to be on main.

1190
01:00:29,927 --> 01:00:32,627
Because all I'm gonna do is tell my document,

1191
01:00:32,696 --> 01:00:35,797
which is part of my model, extended part of my model.

1192
01:00:35,865 --> 01:00:39,167
I'm just gonna tell that it changed. That's not anything

1193
01:00:39,235 --> 01:00:42,304
UI, so I don't necessarily have to do that here. I could

1194
01:00:42,372 --> 01:00:45,473
put nil here and be pretty safe no matter what thread I'm

1195
01:00:45,542 --> 01:00:48,776
broadcasting on. Now I happen to know that my emojiArtView

1196
01:00:48,845 --> 01:00:51,913
is broadcasting from the main thread, right? Because it did

1197
01:00:51,982 --> 01:00:54,115
it when it dropped or when someone resized, clearly,

1198
01:00:54,184 --> 01:00:57,952
I'm on the main queue there. So it wouldn't matter but,

1199
01:00:58,021 --> 01:01:00,155
anyway. Okay so here we go,

1200
01:01:00,224 --> 01:01:03,124
now we do get this notification. Turns out that

1201
01:01:03,193 --> 01:01:07,128
our EmojiArtView does not play any music when it broadcasts.

1202
01:01:07,197 --> 01:01:10,031
It could, it could maybe send you the label that it added or

1203
01:01:10,099 --> 01:01:12,567
changed or something. But it doesn't, that's okay.

1204
01:01:12,636 --> 01:01:16,671
We don't care, because all we wanna know is that something

1205
01:01:16,740 --> 01:01:20,575
changed so we can say documentChanged, right? That's

1206
01:01:20,644 --> 01:01:24,446
it, now, of course, we need to stop listening to this.

1207
01:01:24,515 --> 01:01:26,047
When is a good time to do that?

1208
01:01:26,116 --> 01:01:28,516
I'm gonna do that when you hit close.

1209
01:01:28,585 --> 01:01:31,152
And I'm gonna do it whether or not you successfully closed

1210
01:01:31,221 --> 01:01:33,254
because I'm gonna get dismissed. So

1211
01:01:33,323 --> 01:01:35,624
I'm gonna most definitely stop listening here.

1212
01:01:35,692 --> 01:01:40,028
And I'm just gonna say if I can let observer,

1213
01:01:40,096 --> 01:01:46,200
observer = my emojiArt.View observer, art view observer.

1214
01:01:46,269 --> 01:01:50,439
Then I'm gonna ask the notification center,

1215
01:01:50,507 --> 01:01:55,310
the default one, to remove that observer. And

1216
01:01:55,379 --> 01:01:58,513
that's it, so this is quite a bit simpler than delegation,

1217
01:01:58,581 --> 01:02:00,648
on both sides. I's a little easier to do this.

1218
01:02:00,717 --> 01:02:02,050
You don't have to implement that another method.

1219
01:02:02,118 --> 01:02:03,218
You don't have to set yourself to delegate.

1220
01:02:03,287 --> 01:02:03,985
You do't have to do that.

1221
01:02:04,054 --> 01:02:06,020
You just start listening and stop listening and

1222
01:02:06,089 --> 01:02:09,023
you're going to find out. So that's why we use notification

1223
01:02:09,092 --> 01:02:11,726
a lot of times in place where other times we've used

1224
01:02:11,794 --> 01:02:14,662
delegation and it's true in other classes, as well.

1225
01:02:14,731 --> 01:02:17,399
All right, so let's go see if we broke anything. Cross our

1226
01:02:17,467 --> 01:02:20,167
fingers that removing delegation entirely from our

1227
01:02:20,236 --> 01:02:23,371
mode emoji.Art.ViewController did not break anything.

1228
01:02:23,440 --> 01:02:25,440
And luckily, we have that other observing going on, so

1229
01:02:25,509 --> 01:02:27,709
we'll be able to tell. So here's apple bee,

1230
01:02:27,777 --> 01:02:31,412
let's bring up our Console there, change to normal,

1231
01:02:31,481 --> 01:02:34,582
that's good. Now, hopefully when we drop something in,

1232
01:02:34,651 --> 01:02:37,251
hopefully, that caused the radio station broadcast to

1233
01:02:37,320 --> 01:02:39,654
happen so that we notice something is different.

1234
01:02:39,723 --> 01:02:43,058
And hopefully, this is going to auto save in a moment,

1235
01:02:43,126 --> 01:02:45,727
and we can force the issue by threatening to

1236
01:02:45,795 --> 01:02:49,831
go somewhere else. Woo, it did it. So, it must have been

1237
01:02:49,900 --> 01:02:53,000
that our radio station worked. And we noticed that change,

1238
01:02:53,069 --> 01:02:56,637
otherwise we wouldn't have auto saved there. Okay

1239
01:02:56,706 --> 01:03:00,308
the last thing we're gonna do is use KVO to rip out some of

1240
01:03:00,376 --> 01:03:04,111
that code that's calling the delegate and posting down in

1241
01:03:04,180 --> 01:03:07,615
my gesture view. Basically what I wanna do is go

1242
01:03:07,683 --> 01:03:12,053
to my gestures right here, and I wanna remove this code.

1243
01:03:12,121 --> 01:03:14,822
See, this is the code where I'm telling my delegate and

1244
01:03:14,891 --> 01:03:17,259
posting on the radio station when, in this case,

1245
01:03:17,327 --> 01:03:19,760
something moved. So I want that out of there,

1246
01:03:19,829 --> 01:03:23,198
and then down here for resize, this is when we resize,

1247
01:03:23,266 --> 01:03:26,434
I want this out of there. So I'm just gonna delete that.

1248
01:03:26,503 --> 01:03:31,139
But I obviously, still need to tell people when I change.

1249
01:03:31,207 --> 01:03:34,809
So I'm gonna go back to my ArtView here. And as soon as I

1250
01:03:34,877 --> 01:03:38,813
add a label, I'm going to have that label be observed for

1251
01:03:38,882 --> 01:03:42,217
its center changing. And if its center changes, I'm going

1252
01:03:42,285 --> 01:03:44,952
to notify my delegate and broadcast on my radio station.

1253
01:03:45,021 --> 01:03:47,221
'm basically gonna do this right here.

1254
01:03:47,290 --> 01:03:50,325
So how do we do that? The trickiest thing about, this,

1255
01:03:50,394 --> 01:03:54,562
it's actually quite easy. We're just gonna to label

1256
01:03:54,631 --> 01:03:58,466
observe, and

1257
01:03:58,534 --> 01:04:03,738
what property observing /. Center.

1258
01:04:05,609 --> 01:04:08,309
And when we observe, we get a closure. The closure's gonna

1259
01:04:08,378 --> 01:04:13,247
pass the label back to us, and that little changed object,

1260
01:04:13,316 --> 01:04:15,917
right there. And we can do whatever we want in here.

1261
01:04:15,986 --> 01:04:18,619
And what do we want to do? We want to do this.

1262
01:04:18,688 --> 01:04:23,358
Tell our delegate and tell the radio station something

1263
01:04:23,427 --> 01:04:27,528
changed. But remember observed returns a cookie. And

1264
01:04:27,597 --> 01:04:30,698
we have to keep that cookie in the heap as long as we want

1265
01:04:30,767 --> 01:04:33,534
this to happen. So I'm gonna do that by having a little

1266
01:04:33,603 --> 01:04:38,306
private var which I'm gonna call my labelObservations.

1267
01:04:38,375 --> 01:04:43,711
Which is gonna be a dictionary with UIViews as the keys and

1268
01:04:43,780 --> 01:04:49,851
these NSKeyValueObservations as the values. Now putting

1269
01:04:49,920 --> 01:04:53,221
things in this dictionary is gonna keep things in the heap.

1270
01:04:53,290 --> 01:04:56,291
But only as long as this EmojiArtView is in the heap.

1271
01:04:56,359 --> 01:04:58,259
As soon as this EmojiArtView leaves the heap

1272
01:04:58,328 --> 01:05:00,328
this will leave the heap and all the observations

1273
01:05:00,397 --> 01:05:03,197
will leave the heap, woo-hoo. So that's what's great about

1274
01:05:03,266 --> 01:05:05,099
this, not having to do that remote observe,

1275
01:05:05,168 --> 01:05:07,969
remove observer thing like you do with notifications. Because

1276
01:05:08,038 --> 01:05:10,437
when things leave the heap naturally the observations

1277
01:05:10,506 --> 01:05:15,176
naturally stop. However, what if we don't leave the heap and

1278
01:05:15,245 --> 01:05:18,312
we remove that subview. We don't have any,

1279
01:05:18,381 --> 01:05:21,415
actually have any UI to remove our emojis.

1280
01:05:21,484 --> 01:05:23,451
They once they're in there, they're there forever. But

1281
01:05:23,519 --> 01:05:26,120
we could imagine putting some sort of gesture that would

1282
01:05:26,189 --> 01:05:29,157
remove them, so we wanna anticipate that day and

1283
01:05:29,226 --> 01:05:32,193
I wanna make sure we remove it. So, first of all let's put

1284
01:05:32,262 --> 01:05:35,529
the observation, KeyValueObservations in here.

1285
01:05:35,598 --> 01:05:40,301
I'm gonna say labelObservations

1286
01:05:40,369 --> 01:05:45,240
sub the label = this observation.

1287
01:05:45,308 --> 01:05:50,145
So this the labelObservation for this label, right. Now I

1288
01:05:50,213 --> 01:05:54,549
have to whenever this view gets removed from super view,

1289
01:05:54,618 --> 01:05:58,152
I have to let this observation leave the heap.

1290
01:05:58,221 --> 01:06:00,221
In other words, I will have to remove it from here.

1291
01:06:00,290 --> 01:06:02,657
Everyone understand that? So how do I do that?

1292
01:06:02,726 --> 01:06:06,494
Well, luckily, there is a nice method in view called

1293
01:06:06,563 --> 01:06:10,865
willRemoveSubview. And of course,

1294
01:06:10,933 --> 01:06:14,135
we're gonna call super.willRemoveSubview. And

1295
01:06:14,204 --> 01:06:17,338
this gets called anytime a view gets removed from me,

1296
01:06:17,407 --> 01:06:20,774
which is perfect. All I'm gonna say here is I'm just

1297
01:06:20,843 --> 01:06:25,212
gonna check to make sure that this view that's being removed

1298
01:06:25,281 --> 01:06:29,150
is actually in the labelObservation tier. So I'm

1299
01:06:29,219 --> 01:06:35,990
gonna say if LabelObservations subview does not equal nil,

1300
01:06:36,058 --> 01:06:41,062
in other words it will have an observation for it.

1301
01:06:41,131 --> 01:06:43,998
Then I'm gonna set the labelObservation for

1302
01:06:44,067 --> 01:06:47,635
that subview to nil. Boom, it just left the heap.

1303
01:06:47,703 --> 01:06:51,105
As soon as I clear that thing out of this it went away.

1304
01:06:51,174 --> 01:06:53,508
It stops observing which is exactly what I want,

1305
01:06:53,577 --> 01:06:54,776
everyone got that?

1306
01:06:54,845 --> 01:06:56,877
So that's all we need to do to do this.

1307
01:06:56,946 --> 01:07:02,483
Let's make sure we didn't break anything here. Okay so

1308
01:07:02,552 --> 01:07:05,319
we got our Apple Bees right here. Let's change something.

1309
01:07:05,388 --> 01:07:07,855
Okay let's take this eight ball and move it over here.

1310
01:07:07,924 --> 01:07:10,091
And then let's try and threaten,

1311
01:07:10,160 --> 01:07:14,061
oops let's get our console up here. [INAUDIBLE] here,

1312
01:07:14,130 --> 01:07:19,233
okay let's threaten to go somewhere else.

1313
01:07:19,302 --> 01:07:24,505
Woo-hoo, it auto saved! It worked again. All right,

1314
01:07:24,574 --> 01:07:29,477
sound good? Back to our slides.

1315
01:07:29,545 --> 01:07:34,482
Good timing here. Now you remember

1316
01:07:34,551 --> 01:07:37,185
we talked about the view controller lifecycle right?

1317
01:07:37,254 --> 01:07:39,453
View will appear, view did appear, all these things.

1318
01:07:39,522 --> 01:07:42,323
Well the same kind of thing happens with your application

1319
01:07:42,392 --> 01:07:44,425
and it kind of goes through this chart up here.

1320
01:07:44,494 --> 01:07:47,061
So, I'm going to talk about how it transitions through

1321
01:07:47,129 --> 01:07:48,296
all these stages, but

1322
01:07:48,365 --> 01:07:51,065
first I'm going to talk about the stages. So first of all

1323
01:07:51,134 --> 01:07:55,569
there is Foreground Inactive and that is where your code is

1324
01:07:55,638 --> 01:07:59,073
running, but you're not getting any UI events. So you

1325
01:07:59,142 --> 01:08:01,943
can't do anything. So you can only do kind of preparation

1326
01:08:02,011 --> 01:08:05,880
work in this space. Then there's Foreground Active.

1327
01:08:05,949 --> 01:08:07,848
This is the normal state you're used to.

1328
01:08:07,917 --> 01:08:10,484
Getting UI events, view controllers coming on screen,

1329
01:08:10,553 --> 01:08:11,886
segueing, you're doing all your stuff.

1330
01:08:11,954 --> 01:08:14,288
This is the normal running state of your app.

1331
01:08:14,357 --> 01:08:18,292
Then there's Background. In the background your code is

1332
01:08:18,361 --> 01:08:21,061
running, you are not getting any UI events,

1333
01:08:21,130 --> 01:08:22,863
you never live here for long,

1334
01:08:22,932 --> 01:08:27,035
maybe 30 seconds. So this is transitory state, so anything

1335
01:08:27,103 --> 01:08:30,338
you do in the background state you gotta do it fast. And

1336
01:08:30,406 --> 01:08:33,974
then you go into this state Suspended. Here your code is

1337
01:08:34,043 --> 01:08:36,911
not running. It's important to understand no code in your

1338
01:08:36,980 --> 01:08:41,516
app anywhere runs. Your app is not getting any CPU cycles.

1339
01:08:41,584 --> 01:08:43,685
Now what's important about this state is that

1340
01:08:43,753 --> 01:08:49,323
you could be killed at anytime in this state. All right,

1341
01:08:49,392 --> 01:08:52,060
so let's talk about how we transition here. One

1342
01:08:52,128 --> 01:08:55,029
transition is launching your app. So when you launch your

1343
01:08:55,098 --> 01:08:57,665
app, you go from not running where your binary is not even

1344
01:08:57,734 --> 01:09:01,602
executing, to briefly, the foreground inactive state,

1345
01:09:01,670 --> 01:09:04,171
and the foreground active state. So you do pass through

1346
01:09:04,240 --> 01:09:06,741
that foreground inactive state briefly on your way to running

1347
01:09:06,809 --> 01:09:09,410
when you launch. Now, another important one is when you

1348
01:09:09,479 --> 01:09:11,279
switch to another application, right?

1349
01:09:11,347 --> 01:09:13,380
So you're the active app, someone's using you, and

1350
01:09:13,449 --> 01:09:15,616
then they switch to another app.

1351
01:09:15,685 --> 01:09:19,287
And when that happens, you go up to Foreground Inactive for

1352
01:09:19,355 --> 01:09:22,857
just a moment, and then all the way down to Background,

1353
01:09:22,926 --> 01:09:25,960
you sit in the Background for maybe 30 seconds, and

1354
01:09:26,029 --> 01:09:28,329
then you move to Suspended. And

1355
01:09:28,398 --> 01:09:30,698
now from Suspended either you get reactivated,

1356
01:09:30,767 --> 01:09:35,870
if they come back to you, or you get killed at some point.

1357
01:09:35,938 --> 01:09:38,539
Those are transitories. When you get killed,

1358
01:09:38,608 --> 01:09:41,275
you go directly from Suspended to Not running.

1359
01:09:41,344 --> 01:09:43,811
You don't pass through some state where you get to run any

1360
01:09:43,879 --> 01:09:47,515
code. Let's talk about

1361
01:09:47,583 --> 01:09:50,952
how you get notified for all of these transitions.

1362
01:09:51,020 --> 01:09:54,388
What happens and what you're supposed to do. Now,

1363
01:09:54,457 --> 01:09:55,590
all of these things I'm going to tell you,

1364
01:09:55,658 --> 01:09:59,160
by the way, not really that important. Because a lot of

1365
01:09:59,229 --> 01:10:02,930
things are taken care of for you. For example, UIDocument,

1366
01:10:02,999 --> 01:10:05,466
you notice how when we threaten to go to another app,

1367
01:10:05,535 --> 01:10:09,303
it autosaved. It knows about these transitions. It's doing

1368
01:10:09,372 --> 01:10:10,905
that for you, so you don't even need to do anything.

1369
01:10:10,973 --> 01:10:13,273
And that's true of a lot of things in iOS. So

1370
01:10:13,342 --> 01:10:14,876
I'm gonna show you all of these things.

1371
01:10:14,944 --> 01:10:16,277
And the way you do it, but most of the time,

1372
01:10:16,346 --> 01:10:18,646
you don't even need to do anything. You just need to

1373
01:10:18,715 --> 01:10:20,581
know that these transitions are happening.

1374
01:10:20,650 --> 01:10:23,217
All right, so the first transition is from Not running

1375
01:10:23,286 --> 01:10:26,287
into this Inactive state, this Foreground Inactive.

1376
01:10:26,355 --> 01:10:29,791
This is kinda like preparing your app. When this happens,

1377
01:10:29,859 --> 01:10:31,592
like all the things that happen here that I'm gonna

1378
01:10:31,660 --> 01:10:34,996
talk about, a method in your AppDelegate.swift, you know

1379
01:10:35,064 --> 01:10:38,365
that stepchild that we keep foisting off into supporting

1380
01:10:38,434 --> 01:10:42,270
files. Actually we did look at it last time. Remember it had

1381
01:10:42,338 --> 01:10:46,507
the thing where you're opening the URL? Remember we

1382
01:10:46,576 --> 01:10:48,943
had that little code in there that we were talking about,

1383
01:10:49,012 --> 01:10:51,512
that UI document browser view controller, handles opening

1384
01:10:51,581 --> 01:10:54,015
the URL for us? So we have looked in there. But

1385
01:10:54,083 --> 01:10:55,182
there's a lot of methods in there.

1386
01:10:55,251 --> 01:10:58,619
And that's what all of these transitions have is they call

1387
01:10:58,687 --> 01:11:00,554
methods in there. And you'll see there's stubs in there.

1388
01:11:00,623 --> 01:11:04,192
If you go look at it there's stubs in there, that have

1389
01:11:04,260 --> 01:11:06,126
commented out stuff that kinda tell you about them.

1390
01:11:06,195 --> 01:11:08,696
So this is all pretty well documented in there.

1391
01:11:08,765 --> 01:11:11,299
By the way, all of these transitions also

1392
01:11:11,367 --> 01:11:14,101
are broadcast on radio stations. So

1393
01:11:14,170 --> 01:11:16,103
you can just sign up and put a closure and

1394
01:11:16,172 --> 01:11:17,471
want this transition to happen,

1395
01:11:17,540 --> 01:11:20,641
a closure could be executed, all right? So that's important

1396
01:11:20,710 --> 01:11:23,244
to know as well. Not so useful for the very first one which

1397
01:11:23,312 --> 01:11:25,979
is application will finish launching with options.

1398
01:11:26,048 --> 01:11:28,683
And application did finish launching with application,

1399
01:11:28,751 --> 01:11:31,251
cuz that's one of the first time you actually write your

1400
01:11:31,320 --> 01:11:36,224
own code. And notice that that thing has a little dictionary

1401
01:11:36,292 --> 01:11:39,260
passed in, right? Application will and did finish

1402
01:11:39,328 --> 01:11:41,962
launching with options. That dictionary tells you

1403
01:11:42,031 --> 01:11:45,566
why you were launched. Now, why would you be launched?

1404
01:11:45,634 --> 01:11:47,901
Well, of course the user might have touched on your icon.

1405
01:11:47,970 --> 01:11:50,604
That's most of the time. But you can also get launched

1406
01:11:50,673 --> 01:11:52,806
because someone wants you to open a document.

1407
01:11:52,875 --> 01:11:53,941
We're EmojiArt, and

1408
01:11:54,010 --> 01:11:55,743
someone wants us to open an EmojiArt document and

1409
01:11:55,811 --> 01:11:58,746
we're not running, we could get launched to do that. You

1410
01:11:58,815 --> 01:12:02,483
can also set up things where you get launched when the user

1411
01:12:02,551 --> 01:12:05,986
walks by a dry cleaner. You can actually register

1412
01:12:06,055 --> 01:12:10,691
a Place in the world and walk by, boom, you'll get launched.

1413
01:12:10,759 --> 01:12:13,894
You can also have this activity continuation thing,

1414
01:12:13,963 --> 01:12:16,631
where you're working in emoji art on your iPad,

1415
01:12:16,700 --> 01:12:18,932
and then you switch over to your iPhone.

1416
01:12:19,001 --> 01:12:20,802
And then in the corner there's a little icon you press.

1417
01:12:20,870 --> 01:12:22,303
Now you're right back in emoji art where you were.

1418
01:12:22,371 --> 01:12:25,973
Well that might have to launch you. You might get

1419
01:12:26,042 --> 01:12:29,543
a push notification. You're using Cloud Kit, something in

1420
01:12:29,612 --> 01:12:32,179
your database changed, you get woken up to say, hey, look,

1421
01:12:32,248 --> 01:12:34,615
you got a push notification for you. So

1422
01:12:34,683 --> 01:12:37,685
there's a lot of reasons you get woken up, and launched,

1423
01:12:37,754 --> 01:12:40,520
and that dictionary will contain all the information

1424
01:12:40,589 --> 01:12:44,525
you need to know about why. It used to be that an application

1425
01:12:44,594 --> 01:12:47,695
will and did finish launching. We built our UI.

1426
01:12:47,764 --> 01:12:50,831
We created a split view. We created a navigation control.

1427
01:12:50,900 --> 01:12:53,534
We put a view controller. We never do that anymore.

1428
01:12:53,603 --> 01:12:55,569
I only mention this because, your final project,

1429
01:12:55,638 --> 01:12:58,038
you're gonna go out and Google things and look Internet. And

1430
01:12:58,107 --> 01:13:01,108
you're gonna see people say, go create a split view in your

1431
01:13:01,177 --> 01:13:03,911
ApplicationDidFinishLaunching with options. No,

1432
01:13:03,979 --> 01:13:06,347
we don't do that. Storyboards, that's how we do it.

1433
01:13:06,416 --> 01:13:09,250
Those answers were pre storyboard. Or

1434
01:13:09,318 --> 01:13:13,054
someone who never got the storyboard story. We build our

1435
01:13:13,122 --> 01:13:16,790
UI in storyboards, not in these method, in this method.

1436
01:13:16,859 --> 01:13:20,761
All right, the next transition is actually coming to

1437
01:13:20,830 --> 01:13:22,830
that inactive state from the other side.

1438
01:13:22,899 --> 01:13:24,398
You were the active app, and

1439
01:13:24,467 --> 01:13:26,200
not you're not gonna be the active app.

1440
01:13:26,268 --> 01:13:28,202
Probably because the user clicked on another app.

1441
01:13:28,271 --> 01:13:30,737
This one is ApplicationWillResignActive,

1442
01:13:30,806 --> 01:13:32,873
because that's what's happening.

1443
01:13:32,942 --> 01:13:36,744
Here you wanna think of this as a the pause button.

1444
01:13:36,812 --> 01:13:39,346
You wanna pause whatever is happening in your app right

1445
01:13:39,415 --> 01:13:42,349
here. So let's say I use the example of an Asteroids game.

1446
01:13:42,418 --> 01:13:45,419
Your shooting Asteroids. You want the whole Asteroid field

1447
01:13:45,487 --> 01:13:50,291
to pause when you get this. And then the next one

1448
01:13:50,359 --> 01:13:54,829
here is a inactive to active, that, unpause.

1449
01:13:56,699 --> 01:13:58,865
So this is ApplicationDidBecomeActive. So

1450
01:13:58,934 --> 01:14:02,069
you kinda wanna have a pause, unpause thing here. Now,

1451
01:14:02,138 --> 01:14:04,338
with a lot of apps, it doesn't make sense. You never pause or

1452
01:14:04,407 --> 01:14:07,341
unpause. They're not that kinda app. They, they just

1453
01:14:07,410 --> 01:14:08,876
are what they are, so you don't have to do anything.

1454
01:14:08,945 --> 01:14:11,779
But if you have an app where things would make sense

1455
01:14:11,848 --> 01:14:14,515
to pause, this is where you pause and unpause in these two

1456
01:14:14,584 --> 01:14:19,486
things. Now, this one, right here, is, someone

1457
01:14:19,555 --> 01:14:22,323
clicked on another app, you've gone through active, inactive,

1458
01:14:22,391 --> 01:14:24,558
now you're going around to this background state.

1459
01:14:24,627 --> 01:14:26,593
This is ApplicationDidEnterBackground.

1460
01:14:26,662 --> 01:14:30,330
It's time right here to batten down the hatches.

1461
01:14:30,399 --> 01:14:33,934
Close your files, get yourself in a situation where you could

1462
01:14:34,003 --> 01:14:36,637
be killed. You've got about 30 seconds here to prepare to be

1463
01:14:36,706 --> 01:14:38,538
killed. You might not be killed,

1464
01:14:38,607 --> 01:14:42,143
but you might be. So you wanna not have any files open,

1465
01:14:42,211 --> 01:14:44,411
that are gonna get corrupted if they get closed, or

1466
01:14:44,480 --> 01:14:49,049
an unsaved data in your app, close things up here. and

1467
01:14:49,118 --> 01:14:51,752
you get 30 seconds to do it. You can ask for an extension,

1468
01:14:51,820 --> 01:14:54,054
short extensions of time, but if you ask too much,

1469
01:14:54,123 --> 01:14:56,457
the system will stop granting you those exceptions,

1470
01:14:56,526 --> 01:14:57,324
extensions.

1471
01:14:57,392 --> 01:15:00,027
So pretty much think about, you've got 30 seconds or so

1472
01:15:00,096 --> 01:15:06,099
to get your hatches battened here. The next one here is

1473
01:15:06,168 --> 01:15:07,801
applicationwillEnterForegro- und.

1474
01:15:07,870 --> 01:15:09,737
So here, you went down the background view,

1475
01:15:09,806 --> 01:15:12,740
you battened down the hatches, and you got activated again.

1476
01:15:12,809 --> 01:15:15,576
You didn't get killed. Here you wanna un-batten down

1477
01:15:15,645 --> 01:15:19,013
the hatches. Open back up the things that you had closed.

1478
01:15:19,081 --> 01:15:20,681
Now, a lot of times you don't need to do anything here,

1479
01:15:20,750 --> 01:15:23,517
because you're opening up things that you closed

1480
01:15:23,586 --> 01:15:26,153
in the battening down the hatches, on demand anyway.

1481
01:15:26,221 --> 01:15:27,622
If you tried to access a file and

1482
01:15:27,690 --> 01:15:30,057
it's not open, well, you'll just open it then. So,

1483
01:15:30,125 --> 01:15:31,792
oftentimes you don't have to do anything here, and

1484
01:15:31,861 --> 01:15:35,162
I kinda recommend writing your code in that way. So that you

1485
01:15:35,230 --> 01:15:39,400
don't really ever have to un-batten down the hatches. So

1486
01:15:39,468 --> 01:15:41,235
that's, all the things that happen.

1487
01:15:41,303 --> 01:15:43,904
And of all those things you get radio station, all those

1488
01:15:43,973 --> 01:15:47,274
things that have methods in the app delegates you can do.

1489
01:15:47,343 --> 01:15:50,144
But the AppDelegate does some other things as well in there.

1490
01:15:50,213 --> 01:15:53,748
For example, the opening URL thing we saw last time,

1491
01:15:53,816 --> 01:15:56,517
it also can do background fetching.

1492
01:15:56,585 --> 01:15:57,417
Which is kind of cool.

1493
01:15:57,486 --> 01:15:58,886
Let's say you have a Twitter client, or

1494
01:15:58,954 --> 01:16:01,789
something like that, and when someone launches your app,

1495
01:16:01,857 --> 01:16:03,791
you wanna show them the latest Tweets. Well,

1496
01:16:03,860 --> 01:16:07,061
you can actually say to your app to fetch the latest Tweets

1497
01:16:07,129 --> 01:16:09,429
in the background, even when your app is not running. And

1498
01:16:09,498 --> 01:16:11,999
what'll happen is, it'll get launched, but it won't come on

1499
01:16:12,067 --> 01:16:14,101
screen, and you'll be in that background state for

1500
01:16:14,170 --> 01:16:15,335
a little, little bit of time,

1501
01:16:15,404 --> 01:16:17,805
where you're allowed to make a couple of network requests for

1502
01:16:17,874 --> 01:16:20,808
your 30 seconds or whatever. And then you go back to sleep.

1503
01:16:20,877 --> 01:16:23,477
So, you can do that with AppDelegate. It also manages

1504
01:16:23,545 --> 01:16:26,280
data protection. I don't know if you know this but,

1505
01:16:26,349 --> 01:16:29,382
when your device is locked in the lock screen, apps cannot

1506
01:16:29,451 --> 01:16:33,020
see the data. It's encrypted. It is fully encrypted, so you,

1507
01:16:33,089 --> 01:16:35,422
the apps couldn't do anything if they wanted to.

1508
01:16:35,490 --> 01:16:38,525
So, the AppDelegate will tell you what's going on about

1509
01:16:38,594 --> 01:16:42,496
when you can access the files, things like that. There's also

1510
01:16:42,565 --> 01:16:46,100
a UIApplication, which the AppDelegate is delegate of.

1511
01:16:46,168 --> 01:16:48,035
We never subclassed UIApplication,

1512
01:16:48,103 --> 01:16:51,338
we use the AppDelegate to configure it's functionality.

1513
01:16:51,407 --> 01:16:53,774
However, UIApplication does have a few interesting things.

1514
01:16:53,843 --> 01:16:58,479
Like, it has a method so you can open a URL in another app.

1515
01:16:58,548 --> 01:17:01,948
So, your image gallery, and maybe you asked to open

1516
01:17:02,017 --> 01:17:05,119
an emoji art document. You can ask using that open URL.

1517
01:17:05,187 --> 01:17:07,621
Here's where you register for push notifications.

1518
01:17:07,690 --> 01:17:09,489
So, this is something you have to do if you want that

1519
01:17:09,558 --> 01:17:11,625
Cloud Kit thing to notify you. You have to register for

1520
01:17:11,694 --> 01:17:14,595
push notifications there. You can set the fetch interval for

1521
01:17:14,664 --> 01:17:16,630
that background fetching I talked about.

1522
01:17:16,699 --> 01:17:18,899
Here's where you ask for more time, if you're in

1523
01:17:18,968 --> 01:17:20,968
the background mode, and you need a little bit

1524
01:17:21,037 --> 01:17:24,271
more time to finish up. That's happening in UI application.

1525
01:17:24,340 --> 01:17:27,974
The little spinner in the top left of your device that says

1526
01:17:28,043 --> 01:17:31,812
there's network activity, that's controlled with this

1527
01:17:31,881 --> 01:17:33,947
bool. Unfortunately it's a bool.

1528
01:17:34,016 --> 01:17:36,417
So if you have multiple threads acting as a network,

1529
01:17:36,485 --> 01:17:38,886
they gotta share this bool, it's kind of annoying,

1530
01:17:38,954 --> 01:17:41,521
but. And you can also find out about things,

1531
01:17:41,590 --> 01:17:44,291
like how much time do I have left to run in the background?

1532
01:17:44,360 --> 01:17:46,994
What is that preferred content size category, you know,

1533
01:17:47,062 --> 01:17:49,496
the slider for the font size? What state am I in?

1534
01:17:49,565 --> 01:17:50,564
Am I in the foreground,

1535
01:17:50,633 --> 01:17:51,899
the background, where am I?

1536
01:17:51,968 --> 01:17:55,602
You can find all those things out with UIApplication. All

1537
01:17:55,671 --> 01:17:58,606
right, quickly Info.plist, we already saw Info.plist in your

1538
01:17:58,674 --> 01:18:01,976
homework. You used it to add that app transport security,

1539
01:18:02,044 --> 01:18:06,446
right? You can actually edit this directly in XML,

1540
01:18:06,515 --> 01:18:09,150
you just right click on it and switch to sources XML,

1541
01:18:09,218 --> 01:18:12,485
you can do that.

1542
01:18:12,554 --> 01:18:15,122
will get a snippet of XML from somebody that does something,

1543
01:18:15,190 --> 01:18:17,624
enables something in plist, and you're gonna paste it in

1544
01:18:17,693 --> 01:18:20,727
here. But usually we don't even edit the plist thing

1545
01:18:20,796 --> 01:18:23,630
directly like we do with App Transport Security.

1546
01:18:23,699 --> 01:18:25,399
We edit it in the project settings,

1547
01:18:25,468 --> 01:18:27,634
like we did with the document types, right?

1548
01:18:27,703 --> 01:18:29,936
The document types we had for Emoji Art View, and for

1549
01:18:30,005 --> 01:18:33,941
your image gallery. We edited that all in project settings.

1550
01:18:34,010 --> 01:18:37,912
And the project settings is mostly editing the Info.plist

1551
01:18:37,980 --> 01:18:40,881
indirectly. And finally, we have the capabilities.

1552
01:18:40,950 --> 01:18:42,516
We talked about this with Cloud Kit.

1553
01:18:42,585 --> 01:18:45,219
There are certain things, that to use them you

1554
01:18:45,288 --> 01:18:48,889
have to turn them on. This capabilities tab inside of

1555
01:18:48,958 --> 01:18:51,725
your project settings like this.

1556
01:18:51,794 --> 01:18:55,462
Some of these things require servers, like Apple Pay,

1557
01:18:55,531 --> 01:18:59,934
and iCloud, and Game Center. Some don't, like Maps, and

1558
01:19:00,002 --> 01:19:04,071
Inner App Audio, Home Kit, none of those do.

1559
01:19:04,140 --> 01:19:07,074
The things that require a server, you can only turn

1560
01:19:07,143 --> 01:19:10,544
these on if you are a member of an Apple developer program.

1561
01:19:10,612 --> 01:19:13,613
That costs $99 a year. And you can kinda see why that is,

1562
01:19:13,682 --> 01:19:16,383
because to access these server technologies, they're kinda

1563
01:19:16,452 --> 01:19:18,718
needs to be stuff in that server that knows about you,

1564
01:19:18,787 --> 01:19:20,387
and this providing stuff. Well,

1565
01:19:20,456 --> 01:19:23,723
somebody's got, they gotta know who you are for real.

1566
01:19:23,792 --> 01:19:26,193
You can't just be some random Apple ID out there.

1567
01:19:26,262 --> 01:19:27,794
You wanna be registered in the program.

1568
01:19:27,863 --> 01:19:31,999
And the $99 seems to me to be mostly an administrative fee.

1569
01:19:32,068 --> 01:19:34,769
That's not very much money for the amount of functionality

1570
01:19:34,837 --> 01:19:36,570
that you're getting with all these servers,

1571
01:19:36,639 --> 01:19:39,139
push notifications, all these things. It's all covered in

1572
01:19:39,208 --> 01:19:43,476
one $99 per year fee. I don't have time to cover all these,

1573
01:19:43,545 --> 01:19:45,612
but this is a great place to go look for interesting,

1574
01:19:45,681 --> 01:19:48,749
not covered in lecture things to do. Go look through this

1575
01:19:48,818 --> 01:19:51,018
list and see if you can find something fun to do in there.

1576
01:19:51,087 --> 01:19:54,288
All right, that is it. On Wednesday,

1577
01:19:54,356 --> 01:19:57,191
we're gonna talk about super important topic, and I, this

1578
01:19:57,259 --> 01:19:59,960
is the last topic I cover, really, before you launch into

1579
01:20:00,029 --> 01:20:02,730
your final projects this week, which is segues.

1580
01:20:02,798 --> 01:20:05,833
We know about show segues, and show detail segues, right?

1581
01:20:05,901 --> 01:20:08,068
The navigation controller and the split view controller.

1582
01:20:08,136 --> 01:20:09,937
And we know about modal segues too, a little bit.

1583
01:20:10,005 --> 01:20:12,439
We put put up our emoji art document modally. But

1584
01:20:12,508 --> 01:20:15,342
we're gonna learn pop over segue's, more than just for

1585
01:20:15,411 --> 01:20:17,877
alerts, but pop over segue's in general. Also,

1586
01:20:17,946 --> 01:20:20,714
unwinding segue's, and embed segue's, two kind of under

1587
01:20:20,783 --> 01:20:23,517
appreciated segue's that you can do that are kind of cool.

1588
01:20:23,585 --> 01:20:26,053
We're gonna learn all about that, and I'll be demoing it

1589
01:20:26,122 --> 01:20:29,356
all on Wednesday as well. Next week is Thanksgiving.

1590
01:20:29,425 --> 01:20:32,292
So, you get a week off. That will be great, and

1591
01:20:32,361 --> 01:20:35,462
then we'll back at it the week after. All right,

1592
01:20:35,530 --> 01:20:38,198
see you on Wednesday. >> For
星期三见

1593
01:20:38,267 --> 01:20:47,674
more, please visit us at stanford.edu.
>> 更多课程详见 stanford.edu