WPF Adorner Clipping

Question

I have an ItemsControl in a ScrollViewer. The items in the ItemsControl are expanded to a DataTemplate which basically consists of an Adorner.

Now the problem is, when scrolling, the Visual Children of the Adorner are visible outside the ScrollViewer. Lets say I scroll from the Horizontal Offset 0 to 100, the Visual Children of the Adorner move to the left and are visible next to the ScrollViewer, although they should be hidden. Setting ClipToBounds on the ItemsControl or the ScrollViewer does not work.

I understand, that Adorner are rendered above all elements z-order wise, but they really shouldn't be visible in such cases as with the ScrollViewer. The adorned Element by the way behaves like expected and is not visible through the ScrollViewer.

Is there any easy way to "clip" the Adorners, so that they are only visible in the visible scroll area?

Thanks, Andrej

Answer 1

In the following thread Wei Zhou re-templates the ScrollViewer so the button's Adorner is constrained.

Implement selection highlighting - advice please

Regards David

Answer 2

Setting ClipToBounds on the containing control is not enough. You must set the adorner's IsClipEnabled property too.

Answer 3

I've encountered the same problem when subclassing the WPFToolkit DataGrid to draw an adorner around the current cell.

The content of the ScrollViewer is rendered by a ScrollContentPresenter instance. ScrollContentPresenter has its own adorner layer, which is accessible through the ScrollContentPresenter.AdornerLayer property.

I found that my adorner correctly clips if I add it to that layer.

Answer 4

My solution was to push a clip region onto the drawing context, render whatever I needed, and pop the clipping at the end, like this:

drawingContext.PushClip(new RectangleGeometry(new Rect(0, 0, this.AdornedElement.RenderSize.Width, this.AdornedElement.RenderSize.Height)));
// continue drawing
drawingContext.Pop();

You can plug this in into any Adorner, the bounds are already available as part of the element.