private void dragDropManager_OnDragOver(object sender, TreeListDragOverEventArgs e)
        {
            if (e.HitInfo.InRow)
            {
                var view = (TreeListView) e.Manager.View;
                TreeListNode targetNode = view.GetNodeByRowHandle(e.HitInfo.RowHandle);
                var dropTargetType = e.Manager.ViewInfo.DropTargetType;

                var target = (MaterialDto)targetNode.Content;

                if (dropTargetType == DropTargetType.InsertRowsIntoNode && (!target.IsFolder))
                {
                    e.AllowDrop = false;
                    e.Handled = true;
                }
            }
        }
		TreeListDragOverEventArgs RaiseDragOverEvent(TreeListViewHitInfo hitInfo, DragDropManagerBase sourceManager) {
			TreeListDragOverEventArgs e = new TreeListDragOverEventArgs(hitInfo, sourceManager.DraggingRows) {
				Handled = false,
				Manager = this,
				SourceManager = sourceManager,
			};
			if(DragOverEventHandler != null)
				DragOverEventHandler(this, e);
			return e;
		}