AvaloniaPropertyChangedEventArgs

[germgerm]

how/where is AvaloniaPropertyChangedEventArgs ever used ?
OnPropertyChanging takes a PropertyChangingEventArgs which is not castable to AvaloniaPropertyChangedEventArgs.
I am trying to access old/new values which are properties of AvaloniaPropertyChangedEventArgs but not PropertyChangingEventArgs

[stevemonaco]

When you subscribe to an AvaloniaProperty's Changed event. eg.

static MyControl()
{
    ExampleProperty.Changed.Subscribe(OnExampleChanged);
}

private static void OnConditionChanged(AvaloniaPropertyChangedEventArgs args)
{
    if (args.Sender is not MyControl myControl)
        return;

    myControl.DoSomething();
}

See NumericUpDown make use of the approach:

Avalonia/src/Avalonia.Controls/NumericUpDown/NumericUpDown.cs

Lines 368 to 370 in 9e24f9b

	static NumericUpDown()
	{
	NumberFormatProperty.Changed.Subscribe(OnNumberFormatChanged);

For personal projects, you'll need to bridge the observable to Avalonia, too, with something like:

using Avalonia.Reactive;
using System;

namespace MyApp;
internal static class ObservableExtensions
{
    public static IDisposable Subscribe<T>(this IObservable<T> source, Action<T> action)
    {
        return source.Subscribe(new AnonymousObserver<T>(action));
    }
}

PropertyChanged is for the ViewModel-side, the above is for the Avalonia side. At least one approach to it.

[germgerm]

thanks, i am still navigating things and the i guess the distinction between viewmodel code and view code wasn't sinking in