Question

I have a custom control, a range slider, which is used in one of my views.

The constructor looks like this:

        EventHandler ReCalculateWidthsHandler;
        public RangeSlider()
        {
            ReCalculateWidthsHandler = OnReCalculateWidths;
            DependencyPropertyDescriptor.FromProperty(ActualWidthProperty, typeof(RangeSlider)).
                AddValueChanged(this, ReCalculateWidthsHandler);
        }

I do not know when/how I can unscubscribe that event handler. There is no Dispose method in Control. Is there any way I can be notified that the control is being disposed/removed so that I can unsubscribe any subscribed events?

This can be a more general question: Given a custom control that extends Control, how can you tell when it is disposed?

Thank you.

Answer 1

Usually, you should use OverrideMetadata to add change handler for dependency property. Unfortunately it doesn’t work for read only properties. That’s why you use property descriptor I think. You know this way is too complicated because AddValueChanged stores static strong reference which cause memory leak. I think you should call ReCalculateWidthsHandler from the SizeChanged event instead of subscribing to property descriptor.