Thanks a lot for your code, it made overlays very easy to understand for me.

About keyboard navigation remaining active in the background:
experimenting with keyboard focus was a big pain and did not give satisfying results (I may have done it wrong) so my solution, to make sure the user can only interact with the following is to do the following:

using (OverlayAdorner.Overlay(LayoutRoot))
{
// disable the whole background
layoutRoot.IsEnabled = false;

// do some stuff here while overlaid
}

Obviously layoutRoot has to be enabled again when the overlay is disposed of.

This may be ugly and bruteforce-y, but it does the job. Kinda. Indeed if layoutRoot has many items, then it will take some time to render all of them disabled, and this may mess up any animation done to make the overlay appear.

Seems that I needed to replace “.DesiredSize” by .”RenderSize” in:

protected override Size ArrangeOverride(Size finalSize)
{
if (_adorningElement != null)
{
Point adorningPoint = new Point(0, 0);
//_adorningElement.Arrange(new Rect(adorningPoint, this.AdornedElement.DesiredSize));
_adorningElement.Arrange(new Rect(adorningPoint, this.AdornedElement.RenderSize));
}
return finalSize;
}

in order to get the overlay correctly resized.