颤抖的GestureDetector ListView

Question

当我在ListView中有一个GestureDetector并且重写onVerticalDragUpdate方法时，ListView无法滚动。
如何都覆盖onVerticalDragUpdate方法，使ListView保持滚动状态？

new GestureDetector(
              onVerticalDragUpdate: (details) => print("a"),
              child: new ListView(
                children: <Widget>[
                  new Text("a"),
                  new Text("a"),
                  new Text("a"),
                ],
              ),
            )

Answer 1

如果要检查DragUpdateDetails，可以将ListView包裹在NotificationListener内。

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      body: NotificationListener(
        onNotification: (notification) {
          if (notification is ScrollUpdateNotification) {
            print('${notification.dragDetails}');
          }
        },
        child: ListView.builder(
          itemCount: 20,
          itemBuilder: (context, index) {
            return ListTile(
              title: Text('Index = $index'),
            );
          },
        ),
      ),
    );
  }