Hello.

I'm using the Drag & Drop framework with many DragSources and many DropTargets.
These are regularily newly instantiated when the user is filtering or updating a list of elements of which each element is a DragSource that can be dragged onto a list of DropTargets.
When the list of DropTargets which is a list of UserControls is cleared and refilled I'm using the Unload event of the UserControl to set IsDropTarget = false. This makes the DragDropManager unregistering the DropTarget as expected. When trying the same with IsDraggable on the DragSources the DragDropManager does not unregister the DragSource properly an keeps on holding a reference in its internal list. So the internal list is constantly growing and the drag drop experience gets more and more stuttering.

After I downloaded the source code an changed UnregisterDragSource to:

protected internal static void UnregisterDragSource(UIElement element)
{
   if (element != null)
   {
      element.RemoveHandler(UIElement.MouseLeftButtonDownEvent, new MouseButtonEventHandler(OnMouseLeftButtonDown));

      if (Instance._dragSources.Contains(element))
      {
         Instance._dragSources.Remove(element);
      }
   }
}

changed the internal list of DragSources is cleaned up as I would expect it.
Is your implementation a bug? Or is it by design and I'm missing something?
Best regards
Holger