Friday Session 1. Debugging and Xcode Tips and Tricks.srt

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知识共享 署名-非商业性使用-相同方式共享 3.0 美国

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Stanford University.
>> 斯坦福大学

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>> Alrighty, well, hi everybody.
>> 大家好

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My name is Jason. I'm one of your two TAs.
我是 Jason，两个教师助理中的一个

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Junjie is the other one. She is not here today and
另一位是 Junjie，她今天不在

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we are gonna go over today kinda two different things.

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we are gonna go over today kinda two different things.

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One is just a whirlwind tour of Xcode just to make your

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life a lot simpler for the entire quarter and

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the rest of your life to make it more familiar to you.

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And the other thing is how to use the debugger within Xcode

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in particular.

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than most sections just cuz there's not that much material

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to get through, so we'll be out of here a bit early.

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But um, there is also, there is also no slides or

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anything like that, there is no lecture to give,

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it's just I'm gonna hop right into the demo.

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And feel free to stop me at any point, just shout,

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raise your hand if something is not clear if you wanna,

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you wanna learn more about something or whatever, and

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I'll stop to do that.

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I know we're going through a giant list of key commands.

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It's not like the most engaging lecture, so

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I'll try to be as engaging as possible, but

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uh, it is actually super useful.

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So if, if I want you to have like one take away from,

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from this whole talk, it's that, if you wanna get good at

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using Xcode and you wanna feel fluent when you're using it,

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you actually need to know a lot of key commands.

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It will really help you a lot.

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Xcode from Paul in lectures but actually learning all the

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shortcuts for everything will make your life way simpler.

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And I hope I can kinda convince you today that all

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this stuff is actually pretty intuitive.

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It's not just like memorizing a bunch of random things, but

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it's all laid out by Apple in a very nice and, and

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orderly way.

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So let's just dive right in.

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I'm gonna pop up an Xcode here and I have Concentration open,

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which is the end of Wednesday's lecture,

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we had this code working.

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The catch here though is that this version of Concentration

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that I'm using right now, I've deemed it sad Concentration.

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You can see right here on this folder,

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we're gonna investigate that using the debugger.

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But before we do that, I am gonna hop in and

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give you a tour of Xcode using key commands and what not.

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So you remember things from lecture where you've seen for

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example, you can navigate around all the panes

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by clicking these various buttons, but it's gonna

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get really old really fast when you're coding.

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If you're also

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You can get like five times faster if you just

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learn how things are laid out in some various things.

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So the first thing, I'll just kinda go,

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go through Xcode in order, kinda from the top left.

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The first thing is, all this stuff up here at the top left,

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you can actually do automated by key commands.

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So instead of going up and clicking Run and what not,

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you can do Cmd+R, and that will run.

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So there, there are key commands for

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controlling everything about running and, and stopping and

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all that stuff.

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Um, the next thing I wanna talk about is more important

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which is just how you actually navigate around all of Xcode.

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And so there are key commands for doing things like, if you

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watch the screen right now, I can do this, this, this.

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You get really fast at this stuff.

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We're, were opening up a second editor right now.

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Right, so

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how you can like quickly get your way around Xcode.

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So when I close everything that I just did.

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Suppose that were at a full main screen like this,

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the way that everything is laid out is very logical,

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where the left-most pane, which is called the Navigator,

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is controlled by Cmd+0.

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That's what shows it.

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And then the right-most pane is showed using Cmd+Option+0.

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That's what shows and hides the op, right-most pane.

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And then within each pane, so if I'm on the left pane,

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if I do Cmd+1,2,3,4,5 you see how up on the top left here

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we're going through these tabs?

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1, 2, 3, 4, 5, right?

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And then if I do Cmd+Option+0, and

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I look at these tabs up here, I just do Cmd+Option+1, 2 and

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I can go through all those tabs.

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So it's actually pretty nicely laid out like that.

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You just remember that, Cmd+0 is for showing and hiding and

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then the numbers are for tabbing.

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And then if you add in Option, it does the right side.

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So it's pretty simple.

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If you just do Cmd+Shift+y, it toggles the console and

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the debugger at the bottom which we'll be working with

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more later today.

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And those commands alone are enough to just kind of like

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constantly manage your window size,

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especially if you're programming on a laptop where

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you only have like limited screen real estate.

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It's actually really nice to be able to use those commands

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to quickly navigate around.

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The next thing I'll point out is that, you know from lecture

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that Xcode has uh, two different editors.

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It has the um, the main editor that we' re in right here, and

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it has also this thing called the assistant editor.

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So if we do a Cmd+Option+Enter.

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It pops up in this second pane over here, and

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then we can do Cmd+Enter to go back to just one pane, so

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this is super useful.

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The one thing that I'll point out about this is that,

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if you go to your, your Xcode preferences window,

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we have all these things that we can, that we can toggle and

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we won't go through all

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You can go around and change your font colors and

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all that good stuff.

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recommend that you utilize, which is in Navigation here.

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There's this little check box that says, Navigation uses

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the primary editor, versus using the focused editor, and

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by default, this is set to using the primary editor.

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And that's going to probably torture you if you use certain

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other key commands.

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Let me give you an example.

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One of the key commands is for opening certain files without

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having to navigate there in the,

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in the file navigator over here.

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So let's say that I, we all know that there's

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a file called Card.swift and we wanna open it, all I

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have to do is Cmd+Shift+O for open, type card, and

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then there's Card.swift, and that will open it up.

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Now what if I wanted

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So right here, I am zooming around in the,

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in the right pane and I have the right pane selected.

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If I do Cmd+Shift+O and I go back to ViewController,

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it still opens in the left pane.

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So if you don't have this use focused editor option selected

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it's always going to use the left editor or

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the prime editor for those key commands.

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So that's why you wanna have this box checked, so that now

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when we go over here and we have the right one selected

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and we do card, it opens it over on the right pan.

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Makes sense?

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Cool, so I highly recommend that you do that.

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Okay, the next thing, we're gonna do is actually

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talk about text editing within each window really briefly.

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One thing that I wanna point out is, you haven't dealt with

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this problem yet because your Xcode projects haven't gotten

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very large, but they will get very large.

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There will be lots of code files and

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eventually you'll have hundreds of files in a single

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project when you're making a big Xcode project.

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And one of the things that will help you navigate that is

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to help yourself by leaving Navigation,

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like Navigation helper things throughout your files and

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one way to do that is this comment right here that is

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prefixed with comment mark.

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excuse me.

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below this line.

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this notification in this window up here.

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That's where card touch behavior is and

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it will jump to that point of the file.

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And so you can imagine in big files, using these marks is

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actually super helpful when they're really long,

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something to navigate around.

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The next thing that I'll point out about text editing is,

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it's very useful just to know basic text editing commands.

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Like for example, if you have many lines selected and

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you want to comment them out all of a sudden,

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just Cmd+/ will comment things out like that and

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then Cmd+/ again will undo them.

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Another maybe even more useful thing is when you get yourself

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into a, a nasty state like this.

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Just mess some stuff up for no reason.

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And you can tell that it's really not formatted.

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We can select everything that we want and

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do Ctrl+I, I for indent and it will just

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magically put everything exactly like we wanted.

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So that'll save you a lot of time and headache,

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if things are not, if you,

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if you can't tell things that are nicely indented or not.

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And I'll list these all online on Piazza by the way,

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so it's not like you need to know down what they are.

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I just kinda want to give you the,

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give you the lay of the land here.

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So hopefully we're through the, the fast sorta boring

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part of the lecture where it's just all of the key commands.

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But I highly recommend that you learn all this stuff and

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start getting it into your muscle memory so

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that when you're navigating on Xcode,

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you're not torturing yourself for having to click around

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everywhere and do everything manually.

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The next thing to do is to actually start using

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the debugger.

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we're not actually using the version of concentration

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directly from the end of Wednesday's lecture.

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We're actually using a slightly broken version of it,

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and so let's see what happens when we actually run this one.

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I'm gonna run it on the iPhone X simulator using

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our trusty Cmd+R key command, and let's see what happens.

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So I've crashed, it doesn't even work right from

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the start, and we're thrown to the app delegate,

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which is the main file.

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It's crashing on the main method it says, but

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that's not very helpful.

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So the way that we first get more insight into this,

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is to look into the actual stack trace,

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which shows up in the console log down here.

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And you just see this huge stack trace,

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which goes all the way into the internals of iOS,

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all the way down through UI kit,

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and core foundation, and all this stuff, and

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it's not very helpful to see all these memory addresses.

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But if you scroll up to the top in almost every case you

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will see what the actual reason for

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terminating the app was.

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And in this case it tells us that there's an uncaught

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exception called UnknownKeyException,

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which we may might not know what that is.

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It tells us that the reason for the crash was, oops,

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sorry.

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The reason for

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so it already tells us what file something is happening

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in, has some error on setValue:forUndefinedKey.

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Unclear exactly what that is,

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cuz we didn't write that method, and then this class is

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not key value coding-compliant for the key flipCountLabel.

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So that gives us even more insight, is something is wrong

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with flipCountLabel, and so if we go into view controller,

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and we go check out flipCountLabel,

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we actually see flipCountLabel abbreviated to LBL here,

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which is not what it says in the debugger.

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Can anyone figure out what's actually going on here?

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How does it know to print out flipCountLabel?

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Any ideas?

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If we've named it flipCountLbl,

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then why is it printing out flipCountLabel?

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Can anyone think of why?

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No?

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Yeah, in the back.

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Yeah, exactly.

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So that's what I named it.

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What he said was,

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So if we go over to the storyboard over here,

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actually let's just open up both side-by-side using all of

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our happy new key commands.

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So we got the storyboard open over here.

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I'm gonna make this fullscreen for a moment,

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cuz it's easier to see what's going on.

247
00:10:43,810 --> 00:10:44,476
If we look inside here,

248
00:10:48,781 --> 00:10:51,782
Now this right here, that I've selected,

249
00:10:51,851 --> 00:10:54,685
is not actually the official name of the object.

250
00:10:54,754 --> 00:10:58,390
If I open up our assistant editor over here, and

251
00:10:58,458 --> 00:11:00,558
I go over to the view controller, and

252
00:11:00,627 --> 00:11:03,494
I look at its rightmost pane, this is where we see all of

253
00:11:03,563 --> 00:11:04,663
the things that we've connected, and

254
00:11:06,633 --> 00:11:09,567
on the storyboard what they're actually connected to.

255
00:11:09,636 --> 00:11:11,569
Here's where you see that we have this outlet.

256
00:11:11,638 --> 00:11:14,271
The name of the outlet is Flip Count Label, and it's

257
00:11:14,340 --> 00:11:17,175
connected to flipCountLabel, but if you zoom in here,

258
00:11:17,244 --> 00:11:20,244
you'll notice that there's a little exclamation point or

259
00:11:20,313 --> 00:11:22,714
an empty thing, as compared to the normal dot.

260
00:11:22,783 --> 00:11:24,682
So that's it telling you that this thing actually can't

261
00:11:24,751 --> 00:11:27,318
find what it's actually connected to.

262
00:11:27,387 --> 00:11:29,654
So if we go back over into our View Controller,

263
00:11:29,723 --> 00:11:30,655
in this editor, and

264
00:11:38,865 --> 00:11:41,166
And then we go back to the storyboard editor,

265
00:11:41,234 --> 00:11:44,035
we should see that, that error is no longer there, and

266
00:11:44,103 --> 00:11:46,504
we actually have Flip Count Label connected.

267
00:11:46,573 --> 00:11:49,407
So this is a bug that you'll probably see often at first,

268
00:11:49,476 --> 00:11:52,377
as you're not quite, I mean, it's just hard to keep your

269
00:11:52,445 --> 00:11:54,745
storyboard in sync with your code sometimes.

270
00:11:54,814 --> 00:11:57,581
So just know that there's this error about key value coding

271
00:11:57,650 --> 00:11:59,484
compliance and that's what it means.

272
00:11:59,553 --> 00:12:01,152
That you should go check this right most

273
00:12:01,220 --> 00:12:03,120
pane with your View Controller selected, and

274
00:12:03,189 --> 00:12:04,956
that will help you get rid of these errors.

275
00:12:05,025 --> 00:12:06,524
Cool, so we're gonna save that, and

276
00:12:06,592 --> 00:12:07,759
then we're gonna run it.

277
00:12:16,569 --> 00:12:18,803
Okay great, so it's actually running now.

278
00:12:18,872 --> 00:12:21,272
So if you click around to play the game.

279
00:12:21,341 --> 00:12:26,243
Oops, it crashed, and so if I look down inside the console

280
00:12:26,312 --> 00:12:29,713
here, I don't actually have any logs.

281
00:12:29,782 --> 00:12:32,316
It didn't actually show me in the console why it crashed.

282
00:12:32,385 --> 00:12:34,919
In fact, I have no info anywhere.

283
00:12:34,987 --> 00:12:36,220
Let's try and run it again and

284
00:12:36,289 --> 00:12:38,356
see if we can figure out what causes it to crash.

285
00:12:38,425 --> 00:12:39,557
It looked like that time it crashed when

286
00:12:39,626 --> 00:12:40,291
I clicked on a card.

287
00:12:43,763 --> 00:12:47,365
Okay, that time, it let me click on one of the cards, but

288
00:12:47,434 --> 00:12:50,735
it still crashed, so let's try it again.

289
00:12:50,803 --> 00:12:52,770
Let's see if we can figure out some sort of pattern for

290
00:12:52,839 --> 00:12:53,638
what's going on.

291
00:12:56,509 --> 00:12:59,076
That time it crashed after four cards.

292
00:12:59,145 --> 00:13:01,679
So does anyone have an idea for how we can actually start

293
00:13:01,748 --> 00:13:03,414
figuring out how to debug this?

294
00:13:03,482 --> 00:13:04,015
Like how on Earth are we

295
00:13:05,485 --> 00:13:08,386
It seems to be crashing randomly after some number

296
00:13:08,455 --> 00:13:09,220
of cards, and

297
00:13:15,795 --> 00:13:16,728
Anyone have an idea?

298
00:13:18,531 --> 00:13:20,898
Even if you think it's silly, just say something.

299
00:13:20,967 --> 00:13:22,200
Say one way we can do this.

300
00:13:22,268 --> 00:13:23,034
Print statements?

301
00:13:23,102 --> 00:13:23,935
Yeah, print statements.

302
00:13:25,671 --> 00:13:27,538
frustrating if you were in a really big app though.

303
00:13:27,607 --> 00:13:29,106
But you already see the problem with print

304
00:13:29,175 --> 00:13:31,175
statements is, if we're gonna use print statements,

305
00:13:31,244 --> 00:13:33,311
what the heck are we gonna do, go inside every method, and

306
00:13:33,380 --> 00:13:34,812
type print at every point in the method,

307
00:13:34,881 --> 00:13:36,514
and figure out where, and what's going on?

308
00:13:36,583 --> 00:13:37,849
We have to inspect our entire app,

309
00:13:37,917 --> 00:13:40,484
imagine we had like a 100,000 lines of code that'd be really

310
00:13:40,553 --> 00:13:41,085
frustrating.

311
00:13:44,424 --> 00:13:47,558
think about when the actual app is crashing.

312
00:13:47,626 --> 00:13:49,593
At what point is it crashing?

313
00:13:49,662 --> 00:13:51,662
When you flip a card.

314
00:13:51,731 --> 00:13:52,830
When I flip a card.

315
00:13:52,899 --> 00:13:54,065
Can you use a break point somewhere?

316
00:13:54,133 --> 00:13:56,034
Bingo, so you say, just using a break point,

317
00:13:56,102 --> 00:13:58,369
because it's definitely crashing when we flip a card.

318
00:13:58,438 --> 00:13:59,571
So that's a new idea.

319
00:14:03,409 --> 00:14:04,908
inside that method.

320
00:14:04,977 --> 00:14:07,378
And then that will help us hopefully figure out,

321
00:14:07,447 --> 00:14:10,281
when the crashing happens we'll be able to step through,

322
00:14:10,350 --> 00:14:12,517
and hopefully figure out what's going on.

323
00:14:12,585 --> 00:14:14,319
So the way break points work in Xcode,

324
00:14:14,387 --> 00:14:16,888
and if you haven't used break points before it's a way

325
00:14:16,956 --> 00:14:19,457
for your debugger to pause execution of your program on

326
00:14:19,525 --> 00:14:21,258
a certain line of code.

327
00:14:21,327 --> 00:14:23,628
So if we go inside the touchCard method,

328
00:14:23,696 --> 00:14:24,995
which is we know, the first thing that

329
00:14:25,064 --> 00:14:27,465
happens directly when we click on a card.

330
00:14:27,533 --> 00:14:30,701
We can click over here on the left pane on the line of code,

331
00:14:30,770 --> 00:14:32,437
and it pops up this little blue arrow, and

332
00:14:32,505 --> 00:14:33,871
that's what a break point is.

333
00:14:33,940 --> 00:14:36,307
And that instructs the debugger to please stop there

334
00:14:36,375 --> 00:14:37,175
when we get there.

335
00:14:40,380 --> 00:14:43,447
in the left down here, and you can see that it has this

336
00:14:43,516 --> 00:14:46,551
little blue arrow that looks just like this one, and

337
00:14:46,619 --> 00:14:48,753
when I click on it it turns into grey,

338
00:14:48,821 --> 00:14:51,189
which means break points are disabled.

339
00:14:51,257 --> 00:14:53,223
All break points in the entire program are disabled, so

340
00:14:53,292 --> 00:14:55,293
if you want break points to be enabled you have to activate

341
00:14:55,362 --> 00:14:56,628
them this way.

342
00:14:56,696 --> 00:14:59,563
There's also a pane, up inside the navigator over here,

343
00:14:59,632 --> 00:15:02,400
that looks the same way, and it'll show you a list of all

344
00:15:02,468 --> 00:15:04,835
your break points throughout your entire Xcode project.

345
00:15:04,904 --> 00:15:06,037
So, you can also go up here to this pane.

346
00:15:08,441 --> 00:15:09,874
do with break points than just this.

347
00:15:09,943 --> 00:15:12,877
You can also go to this little plus at the bottom left of

348
00:15:12,946 --> 00:15:16,180
this pane, and you can set certain special break points.

349
00:15:16,248 --> 00:15:18,916
So for example, there's one called an exception break

350
00:15:18,985 --> 00:15:21,051
point, so if I add that, what this does is,

351
00:15:21,120 --> 00:15:22,687
anytime an exception is thrown,

352
00:15:22,755 --> 00:15:24,555
if you throw an exception in your app,

353
00:15:24,624 --> 00:15:27,391
instead of just throwing the exception to the console, or

354
00:15:27,460 --> 00:15:30,528
crashing, or what not, it'll actually always, by default,

355
00:15:30,597 --> 00:15:32,963
open the debugger and pause on that line of code.

356
00:15:33,032 --> 00:15:34,732
So if you just always have this all exceptions

357
00:15:34,800 --> 00:15:36,467
break point running that will actually help

358
00:15:36,535 --> 00:15:38,002
you in your developing for example, so

359
00:15:38,070 --> 00:15:40,204
you can actually customize break points here that way.

360
00:15:40,273 --> 00:15:42,840
You can also disable individual break points from

361
00:15:42,909 --> 00:15:43,474
this pane.

362
00:15:46,112 --> 00:15:47,879
the one that we just set right here, but

363
00:15:47,947 --> 00:15:50,514
this one that I just mentioned about exceptions causing

364
00:15:50,583 --> 00:15:52,783
break points to happen, this one is disabled.

365
00:15:52,852 --> 00:15:54,452
So you can selectively go enable and

366
00:15:54,520 --> 00:15:56,988
disable break points all across every file off on this

367
00:15:57,056 --> 00:15:58,756
one pane, which is nice.

368
00:15:58,824 --> 00:16:00,224
But oftentimes all that you need to do,

369
00:16:00,292 --> 00:16:02,059
I'm gonna disable the exceptions one.

370
00:16:02,128 --> 00:16:04,161
Oftentimes all that you need to do is actually within

371
00:16:04,230 --> 00:16:07,331
an individual file, set the break point in that one file.

372
00:16:07,400 --> 00:16:09,033
So okay if we run the program now.

373
00:16:13,572 --> 00:16:16,507
When I click on a card we'll see that what happens is we

374
00:16:16,576 --> 00:16:18,176
end up on this line of code.

375
00:16:19,312 --> 00:16:21,712
So the program is paused at

376
00:16:21,781 --> 00:16:24,048
this line where we're setting off the card number.

377
00:16:24,116 --> 00:16:26,250
And the first thing to point out is that you'll notice

378
00:16:26,319 --> 00:16:28,619
in the debugger itself we actually have a trace of

379
00:16:28,688 --> 00:16:31,355
everything that's stored off in memory at this point.

380
00:16:31,424 --> 00:16:34,625
So self would refer to the view controller in this case.

381
00:16:34,694 --> 00:16:36,160
And you can see if I zoom in, you can see

382
00:16:36,229 --> 00:16:38,096
that it says concentration view controller and

383
00:16:38,164 --> 00:16:40,464
this is the memory address of the view controller, but

384
00:16:40,533 --> 00:16:42,867
it not only gives you that, it gives you a drop down menu

385
00:16:42,936 --> 00:16:45,669
with all of the things that are instance variables

386
00:16:45,738 --> 00:16:49,040
stored off on that instance of that class.

387
00:16:49,108 --> 00:16:53,911
So things like we have the instance of the actual game

388
00:16:53,980 --> 00:16:57,048
of concentration and that has lots of properties itself.

389
00:16:57,116 --> 00:17:00,184
If it has the array of cards and then it also has that

390
00:17:00,252 --> 00:17:02,786
variable index of the one and only face up card, and we can

391
00:17:02,855 --> 00:17:05,957
expand cards and we can look into each card and then we can

392
00:17:06,026 --> 00:17:07,959
find out that the identifier for that card is five.

393
00:17:08,027 --> 00:17:10,461
So you can actually see all of the things that are stored off

394
00:17:10,529 --> 00:17:13,163
right here, inside of the debugger, so

395
00:17:13,232 --> 00:17:17,034
that's super nice, and we can do that, use that to confirm

396
00:17:17,103 --> 00:17:20,438
something like maybe we want to make sure that.

397
00:17:20,506 --> 00:17:21,839
The identifiers that we've set

398
00:17:21,908 --> 00:17:24,408
actually have an equal number of pairs of options.

399
00:17:24,477 --> 00:17:26,544
So, if we go through,we see that the first one is

400
00:17:26,612 --> 00:17:29,013
identifier five, the second one has identifier three,

401
00:17:29,082 --> 00:17:29,913
third one has four.

402
00:17:29,982 --> 00:17:32,583
Four, okay great, here's a pair.

403
00:17:32,652 --> 00:17:34,818
We shouldn't see another four, right?

404
00:17:34,887 --> 00:17:37,688
There's a one and we should see,

405
00:17:37,756 --> 00:17:41,325
we should see one through six, correct?

406
00:17:41,394 --> 00:17:42,660
And we should see each one twice, so

407
00:17:42,729 --> 00:17:44,795
anyway, that'll be like a way to figure that out quickly

408
00:17:44,864 --> 00:17:46,864
without having go manually and print everything out.

409
00:17:46,932 --> 00:17:49,967
Another thing that we can do at any given point is over

410
00:17:50,036 --> 00:17:53,336
inside the console, LLDB, stands for your debugger,

411
00:17:53,405 --> 00:17:55,740
the DB part stands for debugger.

412
00:17:55,808 --> 00:17:58,309
We can actually print out any object that we want to be able

413
00:17:58,378 --> 00:17:59,076
to inspect it.

414
00:17:59,145 --> 00:18:00,111
So if I do a PO,

415
00:18:05,518 --> 00:18:06,784
Give it a moment.

416
00:18:06,853 --> 00:18:10,254
And you notice it prints out this optional concentration,

417
00:18:10,323 --> 00:18:12,990
because concentration is of type optional.

418
00:18:13,059 --> 00:18:14,458
In this case, it's what's called an implicitly

419
00:18:14,527 --> 00:18:15,326
unwrapped optional.

420
00:18:18,531 --> 00:18:19,897
In other words, it's not nil.

421
00:18:19,966 --> 00:18:22,132
The other value in the enum for an optional is sum.

422
00:18:22,201 --> 00:18:24,902
So we know that concentration is set here.

423
00:18:24,970 --> 00:18:27,871
Another thing we can do is actually we can print out by

424
00:18:27,940 --> 00:18:30,741
just typing p for print so it just works magic

425
00:18:32,578 --> 00:18:35,379
abilities to figure how to format the thing that we need

426
00:18:35,448 --> 00:18:39,584
to print out in the way they think is the best readable.

427
00:18:39,652 --> 00:18:40,485
So if I print out game,

428
00:18:43,389 --> 00:18:47,158
prints out cards, all twelve values and then all the info

429
00:18:47,227 --> 00:18:49,126
that we were just looking at inside the debugger.

430
00:18:49,195 --> 00:18:51,495
But it does it all there formatted very nicely.

431
00:18:51,563 --> 00:18:52,729
And then we know that index of one and

432
00:18:52,798 --> 00:18:53,898
only face up card is nil so

433
00:18:57,303 --> 00:18:58,703
We can also do that for any other object.

434
00:18:58,771 --> 00:19:00,671
So I print out flipCountLabel,

435
00:19:02,475 --> 00:19:04,542
it prints out that its a UI label optional.

436
00:19:05,878 --> 00:19:09,446
It's a UI view, which has a UI responder.

437
00:19:09,515 --> 00:19:12,483
And anyway the point is p is very nice it's very helpful

438
00:19:12,551 --> 00:19:13,951
for printing anything out whatsoever.

439
00:19:15,187 --> 00:19:17,387
So, I'm back to our actual bug, at this point.

440
00:19:17,456 --> 00:19:20,357
We have this problem we're clicking on, we click

441
00:19:20,426 --> 00:19:22,526
on a card and we're stopped at this break point and

442
00:19:22,595 --> 00:19:24,962
we wanna figure out why this thing is crashing.

443
00:19:25,031 --> 00:19:26,530
So the first thing that we might do

444
00:19:26,599 --> 00:19:29,500
to figure out what line we're crashing on in this case,

445
00:19:29,569 --> 00:19:31,135
since we're not getting an exception and

446
00:19:31,204 --> 00:19:34,271
we have no idea what's going on, is we might go use these

447
00:19:34,340 --> 00:19:36,974
navigation options inside the actual debugger here.

448
00:19:37,042 --> 00:19:38,542
So if you look in right here,

449
00:19:38,610 --> 00:19:40,811
we have a few different options right here.

450
00:19:40,880 --> 00:19:43,047
One of them is continue program execution and

451
00:19:43,115 --> 00:19:46,083
what that means is okay we're paused at a break point.

452
00:19:46,152 --> 00:19:48,452
Just continue running the program until we hit the next

453
00:19:48,520 --> 00:19:50,054
break point, or if there are no breakpoints,

454
00:19:50,123 --> 00:19:51,255
just continue running the program.

455
00:19:52,391 --> 00:19:53,524
So let's try that right now,

456
00:19:53,592 --> 00:19:58,128
let's click, let's click on continue running.

457
00:19:58,197 --> 00:19:59,363
Okay, in this case we didn't crash,

458
00:19:59,432 --> 00:20:00,864
that time that we tapped on touch card,

459
00:20:00,933 --> 00:20:02,533
so it's just continuing the program.

460
00:20:02,602 --> 00:20:04,502
We're not on a break point right now, so we click again.

461
00:20:05,871 --> 00:20:07,304
Okay, we're back at the same break point, and

462
00:20:07,373 --> 00:20:08,206
we can continue again.

463
00:20:09,575 --> 00:20:12,676
Oh, and that time the program crashed, and

464
00:20:12,745 --> 00:20:14,078
we're not sure what's going on.

465
00:20:14,147 --> 00:20:16,313
But we know that it definitely happened right after

466
00:20:16,381 --> 00:20:17,948
this first line of touchCard.

467
00:20:18,017 --> 00:20:22,019
So let's see how we can go into a little bit more detail.

468
00:20:28,160 --> 00:20:29,693
>> Okay, so we click on the card again.

469
00:20:29,762 --> 00:20:31,996
Rather than continuing the execution, instead,

470
00:20:32,064 --> 00:20:34,165
we can pick the second option here which is step over.

471
00:20:36,269 --> 00:20:38,001
Oops, saw the little help dialog pop up for

472
00:20:38,070 --> 00:20:39,070
a second there.

473
00:20:39,138 --> 00:20:40,404
I wanna get that pop up on the screen.

474
00:20:43,276 --> 00:20:45,109
So you can step over an instruction.

475
00:20:47,713 --> 00:20:49,713
Let's maybe do the next line of code and

476
00:20:49,782 --> 00:20:52,549
we can keep going like this hoping that this is the time

477
00:20:52,618 --> 00:20:54,619
where the crush actually happens.

478
00:21:00,960 --> 00:21:03,760
And it's not, unfortunately.

479
00:21:03,829 --> 00:21:06,162
So actually it doesn't help us with our problem.

480
00:21:06,231 --> 00:21:07,331
Does anyone have any other ideas?

481
00:21:11,103 --> 00:21:12,502
How do you think we can go further to figure

482
00:21:12,571 --> 00:21:13,904
out what the problem actually is?

483
00:21:15,441 --> 00:21:17,608
Take a look at, take a look at this method here.

484
00:21:26,718 --> 00:21:28,886
Well actually, it didn't crash that time,

485
00:21:28,955 --> 00:21:30,420
so that was kind of a bad exercise.

486
00:21:30,489 --> 00:21:32,389
But I'm just saying, in general,

487
00:21:32,458 --> 00:21:35,025
once we hit the time that it does crash, what's something

488
00:21:35,094 --> 00:21:37,327
else that we could do to actually go further?

489
00:21:37,396 --> 00:21:40,364
Any ideas? >> Set a break point.

490
00:21:42,568 --> 00:21:43,033
>> There we go.

491
00:21:43,102 --> 00:21:43,668
So she just,

492
00:21:45,671 --> 00:21:46,671
inside concentration.

493
00:21:48,541 --> 00:21:50,974
we're also calling other methods inside of touchCard.

494
00:21:51,043 --> 00:21:52,575
And then there's another method after that.

495
00:21:52,644 --> 00:21:54,611
There's also updateViewFromModel,

496
00:21:54,680 --> 00:21:55,313
so actually,

497
00:21:58,116 --> 00:21:59,483
Which means, it can be crashing anywhere inside

498
00:21:59,552 --> 00:22:01,985
the chooseCard, or any where inside updateViewFromModel.

499
00:22:02,054 --> 00:22:04,054
So one thing that we could do is we could go to

500
00:22:04,123 --> 00:22:06,256
both of these methods like updateViewFromModel,

501
00:22:06,325 --> 00:22:07,658
and we can set a break point there.

502
00:22:07,726 --> 00:22:12,429
And then we could pop open a, let's pop open card over here,

503
00:22:12,498 --> 00:22:15,199
and we'll go to chooseCard, oh excuse me

504
00:22:15,268 --> 00:22:17,835
we're go to concentration over here and we'll put a break

505
00:22:17,904 --> 00:22:20,604
point inside choose card and now we have three different

506
00:22:20,673 --> 00:22:24,274
break points set as you can see in the break point pane.

507
00:22:24,343 --> 00:22:28,479
And that'll make it stop at all the places where it could

508
00:22:28,547 --> 00:22:30,247
possibly be at the start of the method.

509
00:22:30,315 --> 00:22:32,883
But another, I'm not gonna do that right now, another way of

510
00:22:32,952 --> 00:22:37,888
doing that actually is to use the The next option inside

511
00:22:37,956 --> 00:22:38,989
the debugger pane.

512
00:22:41,961 --> 00:22:43,260
So if you click on something

513
00:22:45,064 --> 00:22:46,664
Let me get back to one window here.

514
00:22:48,567 --> 00:22:53,137
Once we get to a method, Like chooseCard,

515
00:22:53,206 --> 00:22:55,572
we can see this next option here is step into and

516
00:22:55,641 --> 00:22:58,074
that's how we get inside the actual method, so

517
00:22:58,143 --> 00:23:01,779
if I click step into, now we are at the top of chooseCard.

518
00:23:01,848 --> 00:23:04,047
And now if we want we can step over each line inside of

519
00:23:04,116 --> 00:23:05,249
chooseCard.

520
00:23:05,317 --> 00:23:06,683
And we can inspect the code if we want,

521
00:23:06,752 --> 00:23:08,452
we can read it to make sure everything's okay.

522
00:23:10,757 --> 00:23:12,523
We could put extra break points inside here if we see

523
00:23:12,592 --> 00:23:14,125
something that might be suspicious.

524
00:23:15,360 --> 00:23:16,559
Notice that if we're inside a four loop,

525
00:23:16,628 --> 00:23:18,329
that's a lot of iterations,

526
00:23:18,398 --> 00:23:20,764
it would take forever to step over the whole time.

527
00:23:20,832 --> 00:23:22,399
So you can get yourself in trouble real fast

528
00:23:22,468 --> 00:23:23,833
if you're stepping into methods that

529
00:23:23,902 --> 00:23:25,202
have a lot of behavior going on.

530
00:23:25,270 --> 00:23:27,170
But that aren't relevant to actually what's going on.

531
00:23:27,239 --> 00:23:28,239
But you get the idea.

532
00:23:29,542 --> 00:23:30,107
So let's continue,

533
00:23:33,779 --> 00:23:37,782
Let's, this time let's step inside updateViewFromModel.

534
00:23:40,019 --> 00:23:41,852
So that's the method that's right beneath this one.

535
00:23:42,888 --> 00:23:44,287
And let's step over this.

536
00:23:44,356 --> 00:23:47,324
We're gonna go through all the indices inside cardButtons,

537
00:23:47,393 --> 00:23:49,393
which is kind of a pain because we have to go

538
00:23:49,461 --> 00:23:50,795
through this big for loop and

539
00:23:50,863 --> 00:23:53,697
see if anyone sees anything suspicious in this method.

540
00:23:56,968 --> 00:23:58,803
Just point it out, point it out if you see it.

541
00:24:00,138 --> 00:24:01,405
If something weird is going on.

542
00:24:05,444 --> 00:24:07,377
Anybody?

543
00:24:07,446 --> 00:24:11,715
It's the world's worst line of code of all time.

544
00:24:11,784 --> 00:24:12,616
What is this?

545
00:24:14,286 --> 00:24:14,819
What is this?

546
00:24:14,887 --> 00:24:15,553
Who put this here?

547
00:24:17,656 --> 00:24:20,757
it's information this way to exit your app, right?

548
00:24:20,826 --> 00:24:24,160
So we're just actually exiting with negative 1.

549
00:24:24,229 --> 00:24:28,198
It turns out we're exiting a flipCount, which that thing we

550
00:24:28,267 --> 00:24:31,935
keep in track of at the bottom of that is greater than some

551
00:24:32,003 --> 00:24:35,538
random number that's generated between this.

552
00:24:35,607 --> 00:24:36,974
What the heck? This line couldn't just make

553
00:24:37,042 --> 00:24:37,675
any sense, right?

554
00:24:40,746 --> 00:24:44,348
debugger because it's like it's giving us no information

555
00:24:44,416 --> 00:24:45,349
in the console so

556
00:24:48,754 --> 00:24:52,022
Anyway, so obviously this is the problem, if we get rid

557
00:24:52,090 --> 00:24:54,658
of this completely pointless in same line of

558
00:24:54,727 --> 00:24:57,995
code that I put in there, then we run the program again

559
00:25:04,437 --> 00:25:06,770
We're gonna stop at that break point, so maybe we'll,

560
00:25:06,839 --> 00:25:08,038
we'll disable it this time,

561
00:25:08,107 --> 00:25:10,207
cuz we're not sure if we fixed all of the problems.

562
00:25:10,275 --> 00:25:13,010
So we'll keep that break point there just in case, but

563
00:25:13,079 --> 00:25:14,644
we'll disable it and hit continue.

564
00:25:14,713 --> 00:25:16,614
And then we'll try to play concentration,

565
00:25:18,351 --> 00:25:19,850
See if anything strange is going on.

566
00:25:19,919 --> 00:25:22,719
It actually seems like it's working more this time.

567
00:25:22,788 --> 00:25:23,887
Also, I'm not actually playing right now.

568
00:25:23,956 --> 00:25:25,389
I promise I'm not this bad at this game.

569
00:25:27,026 --> 00:25:28,592
But it looks like we fixed the problem.

570
00:25:28,661 --> 00:25:31,128
And we know we have fixed one problem because there's not

571
00:25:31,197 --> 00:25:33,063
an exit in our code which is kinda ridiculous.

572
00:25:33,132 --> 00:25:35,266
Are there any questions about using the actual debugger?

573
00:25:35,334 --> 00:25:35,933
Are you done here?

574
00:25:38,804 --> 00:25:40,069
Everyone understand kind of the general idea?

575
00:25:40,138 --> 00:25:41,771
It's actually pretty simple, for

576
00:25:41,840 --> 00:25:44,007
navigating around the memory hierarchy and

577
00:25:44,076 --> 00:25:46,476
then using these commands to step through your code.

578
00:25:46,545 --> 00:25:47,177
That's all make sense?

579
00:25:48,514 --> 00:25:50,747
Okay cool, one thing I wanna show you is that

580
00:25:50,816 --> 00:25:52,882
the debugger is not quite as simple as everything that just

581
00:25:52,951 --> 00:25:54,485
appears the pane right here.

582
00:25:54,553 --> 00:25:56,520
It turns out that there's something inside of Xcode's

583
00:25:56,589 --> 00:25:59,256
preferences called behaviors, and this is an Xcode

584
00:25:59,325 --> 00:26:02,025
wide thing, it's actually really useful and cool.

585
00:26:02,094 --> 00:26:04,895
And what behaviors is for various parts of running your

586
00:26:04,963 --> 00:26:08,265
app, and actually gives you the ability

587
00:26:08,333 --> 00:26:11,835
to make custom configurations for when certain events occur.

588
00:26:11,904 --> 00:26:13,637
You can say if this thing happens,

589
00:26:13,705 --> 00:26:15,138
then do this thing to x code.

590
00:26:15,207 --> 00:26:18,341
So for example, right now when we pause inside,

591
00:26:18,410 --> 00:26:21,311
when the app is running, whenever we pause,

592
00:26:21,380 --> 00:26:25,215
we have this option here that says, show the navigator.

593
00:26:26,685 --> 00:26:27,684
We have that checked.

594
00:26:27,753 --> 00:26:30,387
So if we change this to hide, for example,

595
00:26:30,456 --> 00:26:33,524
then when the app pauses, watch what happens.

596
00:26:37,896 --> 00:26:39,129
So you're gonna touch on the card.

597
00:26:40,666 --> 00:26:43,533
Did you notice that the navigator pane on the left

598
00:26:43,602 --> 00:26:45,635
disappeared when that happened?

599
00:26:45,704 --> 00:26:46,370
So that's interesting.

600
00:26:48,640 --> 00:26:51,041
we're debugging, we might want Xcode to just, by default,

601
00:26:51,110 --> 00:26:53,410
just go to a certain state cuz we don't know whenever we're

602
00:26:53,479 --> 00:26:55,712
running the app what state our Xcode is currently in, but

603
00:26:55,781 --> 00:26:57,647
we know that when we're debugging we want it to be

604
00:26:57,716 --> 00:26:58,782
in particular state.

605
00:26:58,851 --> 00:27:00,384
So you can actually go customize all that stuff

606
00:27:00,452 --> 00:27:01,652
inside behaviors.

607
00:27:01,720 --> 00:27:03,987
In the interests of time and sanity, I won't go through

608
00:27:04,056 --> 00:27:05,455
every single little option, like we could play

609
00:27:05,524 --> 00:27:07,758
a sound when certain things happen or whatever.

610
00:27:07,827 --> 00:27:09,560
You can actually go through the Behaviors pane and

611
00:27:09,628 --> 00:27:12,862
kinda check and see everything that it can do for you.

612
00:27:12,931 --> 00:27:14,932
So it's actually pretty useful.

613
00:27:15,000 --> 00:27:15,765
Any questions about behaviors?

614
00:27:15,834 --> 00:27:16,467
Does that make sense?

615
00:27:19,638 --> 00:27:20,571
Okay, great.

616
00:27:23,709 --> 00:27:26,777
a little bit about what actually the Xcode file itself

617
00:27:26,845 --> 00:27:29,479
contains, because it's kind of opaqued people the first time

618
00:27:29,548 --> 00:27:30,413
they have used Xcode.

619
00:27:30,482 --> 00:27:32,448
So this is your actual project file.

620
00:27:32,517 --> 00:27:35,185
It has all these different tabs inside of it, and

621
00:27:35,254 --> 00:27:38,122
there's just a lot going on inside here.

622
00:27:38,190 --> 00:27:41,291
In general, I am not going to go through every little point,

623
00:27:41,360 --> 00:27:43,927
but in general, what I would encourage you to do is

624
00:27:43,996 --> 00:27:46,797
understand the difference between build settings and

625
00:27:46,866 --> 00:27:49,866
what goes on inside of build settings, and build phases,

626
00:27:49,935 --> 00:27:51,035
and what that means.

627
00:27:53,672 --> 00:27:56,039
like figure out what version of our programming language

628
00:27:56,107 --> 00:27:57,207
that we're running with.

629
00:27:57,276 --> 00:27:58,175
That's something that's going to go

630
00:27:58,244 --> 00:27:58,909
into your build settings.

631
00:28:00,679 --> 00:28:03,780
So we can either scroll down and look for that option like,

632
00:28:03,849 --> 00:28:06,883
here we find Swift language version set to Swift 4.0 or

633
00:28:06,952 --> 00:28:09,586
you can actually use this handy thing coz this menu

634
00:28:09,655 --> 00:28:10,987
can get kind of large, and

635
00:28:11,056 --> 00:28:14,157
type something like language, and then, okay, great.

636
00:28:14,225 --> 00:28:17,861
I was just filtering to just Swift language.

637
00:28:17,929 --> 00:28:19,863
So I would encourage you to go through build settings,

638
00:28:19,932 --> 00:28:22,465
and just see what things that there are to change and what

639
00:28:22,534 --> 00:28:25,101
not, and you'll see this, can get actually kind of large,

640
00:28:25,170 --> 00:28:27,738
the more complex your Xcode product is.

641
00:28:27,807 --> 00:28:29,406
Both phases is separate from that.

642
00:28:29,475 --> 00:28:32,509
And the thing that I would point you towards here is,

643
00:28:32,578 --> 00:28:33,977
this is where you see all the source files

644
00:28:34,045 --> 00:28:35,179
that are used inside your app.

645
00:28:38,917 --> 00:28:40,617
Then there's the second section called link

646
00:28:40,686 --> 00:28:42,219
binary with libraries.

647
00:28:42,287 --> 00:28:43,854
So that's if you wanna actually add a library

648
00:28:43,923 --> 00:28:45,822
to use to your project which we are gonna get into later

649
00:28:45,891 --> 00:28:46,457
in this quarter.

650
00:28:49,395 --> 00:28:51,495
besides just putting a label or a button or

651
00:28:51,563 --> 00:28:53,730
any of the stuff that comes stock in UI kit.

652
00:28:53,799 --> 00:28:56,567
Say that we wanted to put like a map because we are making

653
00:28:56,635 --> 00:28:59,469
an app like map something like that what we will do is

654
00:28:59,538 --> 00:29:01,872
add a new library to our app and type in map, and

655
00:29:01,940 --> 00:29:04,908
we find this thing called map kit, and then you type add and

656
00:29:04,976 --> 00:29:08,044
that's where all you're adding for frameworks happens.

657
00:29:08,113 --> 00:29:09,880
And then we see it created this new Frameworks folder

658
00:29:09,949 --> 00:29:12,349
over here, it has a MapKit inside of it.

659
00:29:12,417 --> 00:29:15,385
And now we can go inside any file, like ViewController.

660
00:29:15,454 --> 00:29:19,355
We can go to the top of that file and say import MapKit and

661
00:29:19,424 --> 00:29:21,357
it's there.

662
00:29:21,426 --> 00:29:22,025
Make sense?

663
00:29:24,129 --> 00:29:25,129
the Xcode file for now.

664
00:29:28,100 --> 00:29:30,867
The one caveat I'll talk about with the Xcode file is

665
00:29:30,936 --> 00:29:33,670
if you're using Git or any kind of source control,

666
00:29:33,739 --> 00:29:36,406
you will actually be committing the Xcode project

667
00:29:36,474 --> 00:29:39,409
file itself to the repository and imagine that you're

668
00:29:39,478 --> 00:29:42,345
working on source control with other people online.

669
00:29:42,414 --> 00:29:45,048
If two different people have a merged conflict within

670
00:29:45,117 --> 00:29:47,016
the actual Xcode project file itself,

671
00:29:47,085 --> 00:29:49,786
that's just a big file that stores off a bunch of data by

672
00:29:49,855 --> 00:29:52,656
your Xcode project, that can be kind of nasty to learn how

673
00:29:52,725 --> 00:29:54,057
to merge those conflicts.

674
00:29:54,126 --> 00:29:54,825
So that means,

675
00:29:56,662 --> 00:29:59,763
code it might be worth looking up online ways to help manage

676
00:29:59,832 --> 00:30:02,032
the Xcode project file itself inside source control.

677
00:30:02,100 --> 00:30:04,367
Cuz it's not as simple as doing source control inside

678
00:30:04,436 --> 00:30:05,302
an actual code file.

679
00:30:07,406 --> 00:30:09,939
project file that you'll wanna learn about what it actually

680
00:30:10,008 --> 00:30:11,008
looks like internally.

681
00:30:12,111 --> 00:30:13,209
So that's all that I have planned for

682
00:30:13,278 --> 00:30:14,444
today does anyone have any questions or

683
00:30:14,513 --> 00:30:15,345
anything that we went over.

684
00:30:15,414 --> 00:30:16,613
Does all make sense?

685
00:30:18,583 --> 00:30:20,083
key commands in the debugger, yeah sure.

686
00:30:20,152 --> 00:30:23,153
>> Is it possible to do some sort of version control?

687
00:30:23,222 --> 00:30:23,987
>> Or right sure, so

688
00:30:26,791 --> 00:30:29,526
So I was just sort of alluding to that when I was talking

689
00:30:29,595 --> 00:30:31,861
about the Xcode project file itself.

690
00:30:31,930 --> 00:30:35,098
The answer is yes, you can use source control.

691
00:30:35,166 --> 00:30:37,267
Most people, pretty much everybody these days uses GIT.

692
00:30:37,335 --> 00:30:39,035
So highly recommend you go learn GIT.

693
00:30:39,104 --> 00:30:42,906
If you dont know GIT, you can go online and quickly,

694
00:30:42,975 --> 00:30:44,841
I would recommend, there's something called PRO GIT.

695
00:30:44,910 --> 00:30:49,947
And that's a free book that you can learn online.

696
00:30:50,015 --> 00:30:50,981
Learn from online.

697
00:30:56,121 --> 00:30:58,788
Okay, great, so here's this book called Pro Git.

698
00:30:58,857 --> 00:31:00,323
And if you haven't used Git before,

699
00:31:00,392 --> 00:31:01,925
I highly recommend that you don't just go off and

700
00:31:01,994 --> 00:31:02,859
try to use Git.

701
00:31:02,927 --> 00:31:04,695
I highly recommend that you go off and

702
00:31:04,763 --> 00:31:06,563
you read something like Pro Git first.

703
00:31:06,631 --> 00:31:09,265
So that you actually learn what's going on with Git and

704
00:31:09,334 --> 00:31:11,768
how it represents source control under the hood.

705
00:31:11,836 --> 00:31:14,570
It'll really help you because one of the big pain points for

706
00:31:14,639 --> 00:31:17,374
people, when they are first learning source control is you

707
00:31:17,442 --> 00:31:19,843
learn a few commands for how to commit code online and

708
00:31:19,912 --> 00:31:21,311
how to send it to other people.

709
00:31:21,380 --> 00:31:23,580
But then, when you run into a problem, of some sort, and

710
00:31:23,649 --> 00:31:26,616
you don't know how to undo that problem,

711
00:31:26,685 --> 00:31:28,418
It's really hard to figure out what's going on if you don't

712
00:31:28,487 --> 00:31:29,619
know how to Git actually stores things.

713
00:31:29,688 --> 00:31:31,087
So it's really necessary to go through and

714
00:31:31,156 --> 00:31:34,691
read something like this book to understand how Git works.

715
00:31:34,759 --> 00:31:36,059
And then if you don't have a GitHub account,

716
00:31:36,128 --> 00:31:37,660
go to github.com and

717
00:31:37,729 --> 00:31:39,396
immediately create an account and

718
00:31:39,464 --> 00:31:43,433
start creating your repository and learning all the commands

719
00:31:43,502 --> 00:31:45,135
that are better explained to you inside this book.

720
00:31:45,203 --> 00:31:46,236
I highly recommend that.

721
00:31:49,241 --> 00:31:50,107
in particular,

722
00:31:53,044 --> 00:31:58,782
So I'll do file, new project, I'll create a single view

723
00:31:58,851 --> 00:32:04,754
app,I'll call it test, And then you'll see that when I'm

724
00:32:04,823 --> 00:32:06,989
actually creating the project, I'll put in my desktop here.

725
00:32:07,058 --> 00:32:09,025
It actually has a source control option for

726
00:32:09,094 --> 00:32:10,360
creating a Git repository.

727
00:32:10,428 --> 00:32:12,862
So actually, when you check this it'll, it'll put your

728
00:32:12,931 --> 00:32:15,065
project with a .git file in the actual directory.

729
00:32:15,133 --> 00:32:16,899
And then you can push that online to GitHub.

730
00:32:16,968 --> 00:32:17,968
So it'll do that automatically so

731
00:32:18,037 --> 00:32:18,769
you don't need to do it manually.

732
00:32:22,140 --> 00:32:23,273
Any other questions?

733
00:32:25,110 --> 00:32:25,609
No.

734
00:32:27,045 --> 00:32:27,644
talk to me afterwards.

735
00:32:29,180 --> 00:32:31,114
Thank you all.
谢谢大家

736
00:32:31,182 --> 00:32:35,352
>> For more please visit us at stanford.edu.
>> 更多课程详见 stanford.edu