public void Undo()
 {
     for (int i = 0; i < items.Length; i++)
     {
         collection.InsertInternal(i, items[i]);
     }
     collection.modelProperty.XamlDesignItem.NotifyPropertyChanged(collection.modelProperty);
 }
 public void Undo()
 {
     collection.InsertInternal(index, item);
     collection.modelProperty.XamlDesignItem.NotifyPropertyChanged(collection.modelProperty);
 }