private void AssociatedObject_Loaded(object sender, System.Windows.RoutedEventArgs e)
{
pop = VisualTreeHelperEx.GetChildObject <Popup>(this.AssociatedObject);
if (pop != null)
{
pop.Placement = PlacementMode.Right;
pop.Opened += Pop_Opened;
pop.SizeChanged += Pop_SizeChanged;
}
}