Add TryGetValue() to IPreferences

[maztan]

Description

Currently IPreferences allows checking if the property exists via ContainsKey(string key) method but it would be nice if it had a TryGetValue<T>(string propertyName, out T value)

Public API Changes

Public TryGetValue<T>(string propertyName, out T value) would be added to the IPreferences interface.

Intended Use-Case

More concise code.

[egvijayanand]

Enables checking and retrieving the value in a single method call. Recommended practice for dictionaries.

[jfversluis]

Get already has a default value for if its not found, so although the method name is different, that is basically implemented already? Or what am I missing?

[maztan]

@jfversluis

I marked the line that would go away after the requested change was implemented. Also, current API forces providing default value each time the Get() is called, so this call should be preferably made only once within the range, where the preference's value is needed.

class DummyObservable
{
    IPreferences preferences = Preferences.Default;

    public string MyPref1
    {
        get => preferences.Get(nameof(MyPref1), "some default");
        set
        {
            if (preferences.ContainsKey(nameof(MyPref1)))
            {
                //THIS LINE WOULD GO AWAY AND PROVIDING DEFAULT VALUE SECOND TIME WOULDN'T BE NEEDED
                string currentValue = preferences.Get(nameof(MyPref1), "unneeded default");
                // if new value is null, check if currentValue is also null, in which case they are already equal (but can't call "Equals()" on null).
                if (!(value?.Equals(currentValue) ?? currentValue == null))
                {
                    preferences.Set(nameof(MyPref1), value);
                    OnPropertyChanged();
                }
            }
        }
    }

    public string MyPref2
    {
        get => preferences.Get(nameof(MyPref2), "David");
        set
        {
            if (preferences.TryGetValue(nameof(MyPref2), out string currentValue))
            {
                if (!(value?.Equals(currentValue) ?? currentValue == null))
                {
                    preferences.Set(nameof(MyPref2), value);
                    OnPropertyChanged();
                }
            }
        }
    }

    public event PropertyChangedEventHandler? PropertyChanged;

    protected virtual void OnPropertyChanged([CallerMemberName] string propertyName = "")
    {
        PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(propertyName));
    }
}

MyPref2 uses the method TryGetValue that does not currently exist and is the one requested for implementation.

[jfversluis]

But you don't need if (preferences.ContainsKey(nameof(MyPref1))) because that is already implicit with the default value. If the key doesn't exist, it will return the default value. So in that case the value will never be null and you don't need those checks.

I mean, I see some value, but its mostly writing slightly different code to achieve the same thing you can already do today.

[maztan]

But you don't need if (preferences.ContainsKey(nameof(MyPref1))) because that is already implicit with the default value. If the key doesn't exist, it will return the default value. So in that case the value will never be null and you don't need those checks.

I mean, I see some value, but its mostly writing slightly different code to achieve the same thing you can already do today.

If this was true, the ContainsKey method could be removed from the API altogether. If the default value is null, the call to ContainsKey is still required. Also, this is just one example of potential usage.

[maztan]

For now, I've added this extension method to my codebase. It does not improve performance what a "real" TryGetValue implementation might be able to do, but it matches the functionality.

public static bool TryGetValue<T>(this IPreferences _this, string key, out T? value)
{
    if (_this.ContainsKey(key))
    {
        value = _this.Get<T?>(key, default);
        return true;
    }

    value = default;
    return false;
}

[egvijayanand]

The TryGetValue() method has a subtle advantage because it always returns a Boolean value, making it easy to apply in various scenarios.

[jeremi-przeorek]

I would like to pick this up if that's alright ✋

[jeremi-przeorek]

@egvijayanand how do I navigate to pick this up?

[egvijayanand]

@egvijayanand how do I navigate to pick this up?

You need to get approval for this work item from any one of the maintainers of this repo.

[maztan]

@jeremi-przeorek you need to check out the repository an create a pull request when you are done with the coding

[pictos]

IMHO, It's really easy to add this as an extension method, so devs can implement it by their own if needed and there's no need to add a new API for that on maui

[maztan]

@pictos The existing API is awkward. I would create a PR and see what happens.