Flutter 监听滚动

方案一：Controller

• 1. 可以设置默认的offset;
• 2. 监听滚动，也可以监听滚动的位置；
• 3. 不能监听开始滚动、结束滚动；

class _YZHomePageState extends State<YZHomePage> {

  ScrollController _controller_01 = ScrollController(initialScrollOffset: 300);
  bool _isShowFloatingBtn = false;

  @override
  void initState() {
    // TODO: implement initState
    super.initState();
    _controller_01.addListener(() {
      print("监听到滚动...${_controller_01.offset}");
      _isShowFloatingBtn = _controller_01.offset >= 1000;
        setState(() {
        _isShowFloatingBtn = _controller_01.offset >= 1000;
      });
    });
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
        appBar: AppBar(
            title: Text("列表")
        )
        body: ListView.builder(
          controller: _controller_01,
          itemCount: 100,
            itemBuilder: (BuildContext ctx, int index){
              return ListTile(
                leading: Icon(Icons.people),
                title: Text("联系人$index"),
          );
        }),
      floatingActionButton: _isShowFloatingBtn ? FloatingActionButton(
        child: Icon(Icons.arrow_upward),
        onPressed: () {
          _controller_01.animateTo(0, duration: Duration(seconds: 1), curve: Curves.easeIn);
        },
      ) : null,
    );
  }
}

方案二：NotificationListener

class _YZHomePageState extends State<YZHomePage> {

  ScrollController _controller_01 = ScrollController(initialScrollOffset: 300);
  bool _isShowFloatingBtn = false;

  @override
  void initState() {
    // TODO: implement initState
    super.initState();
    _controller_01.addListener(() {
      // print("监听到滚动...${_controller_01.offset}");
      setState(() {
        _isShowFloatingBtn = _controller_01.offset >= 1000;
      });
    });
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
        appBar: AppBar(
            title: Text("列表")
        ),
        body: NotificationListener(
          onNotification: (ScrollNotification notification) {
            if (notification is ScrollStartNotification) {
              print("开始滚动");
            } else if (notification is ScrollUpdateNotification) {
              print("正在滚动。。。总滚动距离：${notification.metrics.maxScrollExtent}");
            } else if (notification is ScrollEndNotification) {
              print("结束滚动");
            }
            return true;
          },
          child: ListView.builder(
            controller: _controller_01,
            itemCount: 100,
              itemBuilder: (BuildContext ctx, int index){
                return ListTile(
                  leading: Icon(Icons.people),
                  title: Text("联系人$index"),
            );
          }),
        ),
      floatingActionButton: _isShowFloatingBtn ? FloatingActionButton(
        child: Icon(Icons.arrow_upward),
        onPressed: () {
          _controller_01.animateTo(0, duration: Duration(seconds: 1), curve: Curves.easeIn);
        },
      ) : null,
    );
  }
}