protected override void OnItemChanged(object sender, ChangeNotifierEventArgs e)
        {
            base.OnItemChanged(sender, e);
            var tNode = (TNode)sender;

            NameIndex.Add(tNode.Name, tNode);
        }
 private void OnTypesCleared(object sender, ChangeNotifierEventArgs e)
 {
     hierarchies.Clear();
 }
 protected override void OnItemChanging(object sender, ChangeNotifierEventArgs e)
 {
     base.OnItemChanging(sender, e);
     NameIndex.Remove(((TNode)sender).Name);
 }