private void Collection_ItemWentOut(Object Sender, ItemTransferedEventArgs<ShapeBase> E)
{
//Debug.Assert(E.Item.Parent != null, "Non-null parent assertion failed.");
if (Object.ReferenceEquals(E.Item.Parent, this))
E.Item.SetParent(null);
}
private void Collection_ItemCameIn(Object Sender, ItemTransferedEventArgs<ShapeBase> E)
{
//if (E.Item.Parent != null)
// throw new NotSupportedException("Multiple parents not supported.");
E.Item.SetParent(this);
}