How do I handle Canvas.Top change event in WPF?

Question

Hi

I have an element positioned on Canvas using attached properties Canvas.Top and Canvas.Left. Then using animations the element is moved to different set of coordinates, like this:

DoubleAnimation left = new DoubleAnimation( oldLeft, newLeft );
DoubleAnimation top = new DoubleAnimation( oldTop, newTop );

element.BeginAnimation( Canvas.LeftProperty, left );
element.BeginAnimation( Canvas.TopProperty, top );

Is there a way to receive events whenever Canvas.Top or Canvas.Left is changed? Preferably without relation to animation.

Answer 1

One can catch attached property changed event using DependencyPropertyDescriptor's AddValueChanged method:

var descriptor 
    = DependencyPropertyDescriptor.FromProperty( 
        Canvas.LeftProperty, typeof( YourControlType ) 
      );
descriptor.AddValueChanged( this, OnCanvasLeftChanged );