Can I create a generic behavior base class?

[ali50m]

I have some experience with WPF development. I usually create a generic behavior base class and then use it as the base for creating actual behaviors. With this approach I can use the behavior directly on the WPF style or control.

https://stackoverflow.com/a/31292989/6231009

My question is, is there a similar way to create such a generic behavior base class for Avalonia with Avalonia.Xaml.Behaviors nuget?

I tried it with following code, but failed.

<Window
    ...
    behaviors:DragMoveBehavior.IsEnabledForStyle="True"
    ...>
    ...
</Window>

public abstract class AttachableForStyleBehavior<TComponent, TBehavior> : Behavior<TComponent>
    where TComponent : Interactive
    where TBehavior : AttachableForStyleBehavior<TComponent, TBehavior>, new()
{
    static AttachableForStyleBehavior()
    {
        IsEnabledForStyleProperty.Changed.AddClassHandler<TComponent>(HandleEnableChanged);
    }

    private static void HandleEnableChanged(TComponent uie, AvaloniaPropertyChangedEventArgs e)
    {
        var behColl = Interaction.GetBehaviors(uie);
        var existingBehavior =
            behColl.FirstOrDefault(b => b.GetType() == typeof(TBehavior)) as TBehavior;

        switch (e.NewValue)
        {
            case false when existingBehavior is { }:
                behColl.Remove(existingBehavior);
                break;
            case true when existingBehavior is null:
                behColl.Add(new TBehavior());
                break;
        }
    }

    public static readonly AttachedProperty<bool> IsEnabledForStyleProperty =
        AvaloniaProperty.RegisterAttached<TComponent, bool>(
            "IsEnabledForStyle",
            typeof(AttachableForStyleBehavior<TComponent, TBehavior>)
        );

    public static void SetIsEnabledForStyle(TComponent element, bool parameter)
    {
        element.SetValue(IsEnabledForStyleProperty, parameter);
    }

    public static bool GetIsEnabledForStyle(TComponent element)
    {
        return element.GetValue(IsEnabledForStyleProperty);
    }
}

public class DragMoveBehavior : AttachableForStyleBehavior<Window, DragMoveBehavior>
{
    protected override void OnAttached()
    {
        if (AssociatedObject is { })
            AssociatedObject.PointerPressed -= DragMove;
    }

    protected override void OnDetaching()
    {
        if (AssociatedObject is { })
            AssociatedObject.PointerPressed += DragMove;
    }

    private void DragMove(object? sender, PointerPressedEventArgs e)
    {
        if (e.GetCurrentPoint(AssociatedObject).Properties.IsLeftButtonPressed)
            AssociatedObject?.BeginMoveDrag(e);
    }
}

Error message from Visual Studio:
Unable to resolve suitable regular or attached property IsEnabledForStyle on type AvaApp:AvaApp.Behaviors.DragMoveBehavior Line 1, position 2.

Env:
.net 9.0
Window 10
Avalonia 11.2.1
Avalonia.Xaml.Behaviors 11.2.0

Thanks!

[wieslawsoltes]

Seems like Avalonia issue with generic property

[ali50m]

I`m not familar with Avalonia attached property system. Maybe is there other approach for doing this?