Resize ElementHost to size of the hosted XAML UserControl

Question

I would like an expanding panel in my Windows Forms app. I was having a look to see if this would be possible using the WPF Expander control. I\'ve created a Xaml UserControl wh

Answer 1

Yes. You need to override MeasureOverride in your outermost WPF control, convert the size from WPF coordinates to device coordinates, and update ElementHost.Size.

Since you are already subclassing Expander:

1. Override the MeasureOverride method
2. After the measurement is calculated, use PresentationSource.From(visual).CompositionTarget.TransformToDevice.Transform(point) to get the device coordinates
3. Update ElementHost.Size.

Your Expander subclass instance will need a pointer to ElementHost to do this.

A more general solution would be to create a new class to handle the synchronization. It would subclass FrameworkElement and be the direct child of ElementHost.