title: How to make WPF Adorner visible
body: <p>i'm struggling a bit about when or how to activate / make visible a MoveAdorner. </p>
  
  <p>I try the following but have no success: In the element that is to be adorned i add the Adorner in the GotFocus event. That alone did not suffice so i added a call to InvalidateVisual(). But nothing happens. Has anyone a hint on how to make those Adorners Visible?  </p>
  
  <pre><code>    protected void MyUIElement_GotFocus( object sender, RoutedEventArgs e )
      {
          AdornerLayer layer = AdornerLayer.GetAdornerLayer( this );
          layer.Add( new MoveAdorner( this ) );
          layer.InvalidateVisual( );
      }
  </code></pre>
  
  <p>For Clarification: the adorned element is a Control that is positioned inside a derived Panel of a custom ItemsControl.</p>
  
  <p>The <code>MoveAdorner</code> derives from <code>Adorner</code> and simply draws two Boxes on the top and bottom line of the control.</p>
  
  <p>with kind regards</p>