Difficulty when porting WPF control to Avalonia

[mcmikecreations]

Hi! I'm currently rewriting this WPF HexEditor to Avalonia and I have some questions about the performance of different Avalonia functions and about my assumptions for replacing WPF functions with Avalonia ones. I am not very familiar with Avalonia so I may have made some mistakes.

Here are the changes I came up with:

• Loaded event to AttachedToVisualTree because the handler uses Width which should be populated after being attached?
• ActualWidth to Width.
• SizeChangedEvent to a Bounds observable.
• MouseWheelEvent to PointerWheelChangedEvent.
• MouseDownEvent to PointerPressedEvent.
• DropEvent to DragDrop.DropEvent.

Here's what I don't know:

1. What is better to use to register StyledProperty.Changed handlers:

SelectionFirstColorProperty.Changed.AddClassHandler<HexEditor>((x, e) => Control_ColorPropertyChanged(x, e));
SelectionSecondColorProperty.Changed.AddClassHandler<HexEditor>((x, e) => Control_ColorPropertyChanged(x, e));

or

Observable.Merge(
    this.GetPropertyChangedObservable(SelectionFirstColorProperty),
    this.GetPropertyChangedObservable(SelectionSecondColorProperty)
).Subscribe(x => Control_ColorPropertyChanged(this, x));

or

this.GetPropertyChangedObservable(SelectionFirstColorProperty).Subscribe(x => Control_ColorPropertyChanged(this, x));
this.GetPropertyChangedObservable(SelectionSecondColorProperty).Subscribe(x => Control_ColorPropertyChanged(this, x));

2. What is better to use to register a Click handler:
   UndoCMenu.Click += UndoCMenu_Click;
   or
   UndoCMenu.AddHandler(MenuItem.ClickEvent, UndoCMenu_Click);

3. Is there a way to use the property changed signature for validation? I have:

public static readonly StyledProperty<bool> IsStringDataVisibleProperty =
    AvaloniaProperty.Register<HexEditor, bool>(
        nameof(IsStringDataVisible),
        defaultValue: true,
        coerce: Visibility_CoerceValue,
        validate: IsStringDataVisible_ValidateValue
    );

but the validation method in WPF is defined as

private static void StringDataVisibility_ValidateValue(DependencyObject d, DependencyPropertyChangedEventArgs e)

and it is crucial for the logic inside this method to have both d and e. But in Avalonia, validation is done through Func<TValue, bool> which is not suitable in this scenario. How do I overcome this?

4. Lastly, I came across the GetCharFromKey function, which takes a key from the enum and outputs a char from the virtual keyboard. It can be found here. I understand that the code is platform-specific, but is there an existing cross-platform way to implement the method in Avalonia at least on desktop?

I know that I'm asking a lot of questions at once, but getting at least some help would be priceless.

[jp2masa]

ActualWidth corresponds to Bounds.Width.

1. AddClassHandler (in the static constructor) is the best way, because it only subscribes once for all control instances.
2. They're actually equivalent:
   

   Avalonia/src/Avalonia.Controls/MenuItem.cs

   Line 162 in 6332dfc

   add { AddHandler(ClickEvent, value); }

3. I don't think that's validate, if I understand correctly the original is calling this constructor: FrameworkPropertyMetadata, so it would be equivalent to a property changed subscription like 1. (AddClassHandler or StringDataVisibilityProperty.Changed.Subscribe) .
4. That would be something like Keyboard mapping: add mapped key string to raw key event #4447, if I understand correctly? If so, I think there's currently no way of doing that.

[mcmikecreations]

Thanks for all the help! I implemented all of the suggestions and everything seems OK for now. The #4447 not implemented is a shame though, I think many projects would benefit from that, like game editor UI etc.