All the DependencyPropertyKey's in common elements parent classes (FrameworkElement, UIElement, ...) should be protected

[DrkWzrd]

When creating custom controls or framework elements, sometimes we have to handle internally things like IsMouseOver or other readonly dependency properties, inside the code behind of the control.

I don't know if there is a "proper way" to do this, but override OnDependencyPropertyChanged seems wrong to me, because I'm adding overhead for every DP change, and using the corresponding event is fine except there are some properties that doesn't have it (IsMouseOver as example).

Therefore, I'm just using a dirty trick

static ElementChild(){
        //Dirty trick
        var mouseOverPKey = (DependencyPropertyKey?)typeof(UIElement).GetField($"{nameof(IsMouseOverProperty)}Key", System.Reflection.BindingFlags.Static | System.Reflection.BindingFlags.NonPublic)?.GetValue(null);
        mouseOverPKey?.OverrideMetadata(typeof(ElementChild), new FrameworkPropertyMetadata(OnIsMouseOverChangedStatic));

}

And I think this should be allowed by default, just doing the Key protected.

If I am in the wrong and I should do it another way, please, don't hesitate to tell me what is the "proper way" to do it.

[miloush]

Have you tried DependencyPropertyDescriptor.FromProperty(IsMouseOverProperty, typeof(MyElement)).AddValueChanged(this, OnIsMouseOverChanged);?

[DrkWzrd]

It works, albeit not 100% of the time, when the mouse is moved quickly between elements sometimes doesn't fire up correctly and you can be with a mouse over a element and the element had not done what it should do. Directly overriding metadata is much more responsive, I don't know why.

Any way, another API I know for now on. Thanks!