internal static void OnSourceChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
 {
     if (e.IsASubPropertyChange)
     {
         return;
     }
     AVElementHelper.GetHelper(d).MemberOnInvalidateSource(e);
 }
 /// <summary>
 /// Initialization
 /// </summary>
 private void Initialize()
 {
     _helper = new AVElementHelper(this);
 }