private TItem PrivateCreateItem(TIndex index)
        {
            var item = CreateItem(index);
            var args = new IndexedItemCreatedEventArgs <TItem>(item);

            OnItemCreated(args);
            return(item);
        }
 protected virtual void OnItemCreated(IndexedItemCreatedEventArgs <TItem> e) =>
 ItemCreated?.Invoke(this, e);