anchor.diff:            new IconButton(
               icon: new Icon(Icons.more_vert),
               tooltip: 'Show menu',
  -            onPressed: () { showConfigurationSheet(context); },
  +            onPressed: _bottomSheet == null ? _showConfigurationSheet : null,
             ),
           ],
         ),
  
positive.code:           ],
          ),
        );
      });
    }
  
  
negative.code:   static const String routeName = '/list';
  
    @override
    _ListDemoState createState() => new _ListDemoState();
  }
  
  class _ListDemoState extends State<ListDemo> {
    static final GlobalKey<ScaffoldState> scaffoldKey = new GlobalKey<ScaffoldState>();
  
    PersistentBottomSheetController<Null> _bottomSheet;
  