public SecondThirdLevelFoldersPanelVc() {
   super();
   dragController = new ResourceDragController(RootPanel.get(), false, false);
   widgetDropController = new SecondThirdLevelFoldersDropController(this);
   dragController.registerDropController(widgetDropController);
   setDragController(dragController);
 }
 @Override
 public void unregisterDropController() {
   dragController.unregisterDropController(widgetDropController);
 }