Flutter Foundation -028-ScrollController Scroll Monitor

For listening and offset control of lists such as ListView

A constructor

ScrollController({double initialScrollOffset = 0.0,// Initial offset this.keepScrollOffset = true,// Whether to save the scrolling position this.debugLabel, })

Commonly used method

• AnimateTo (), scroll to the specified position, you can set the target offset, time and scroll curve
• JumpTo (), scroll to the specified position and teleport
• AddListener (), to add a scroll listener, can get the scroll position.
• Dispose () is called when dispose of widgets to avoid memory leaks

class _MyHomePageState extends State<MyHomePage> {
  ScrollController controller = new ScrollController();
  bool show = false;
  @override
  void initState() {
    super.initState();
    controller.addListener(() {
      if (controller.offset > 1000 && !show) {
        setState(() {
          show = true;
        });
      } else if (controller.offset <= 1000 && show) {
        setState(() {
          show = false;
        });
      }
    });
  }

  @override
  void dispose() {
    super.dispose();
    controller.dispose();
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text(widget.title),
      ),
      body: ConstrainedBox(
        constraints: BoxConstraints.expand(),
        child: ListView.builder(
          itemBuilder: (BuildContext context, int index) {
            return ListTile(
              title: Text('$index'),
            );
          },
          itemCount: 100,
          itemExtent: 50,
          controller: controller,
        ),
      ),
      floatingActionButton: !show
          ? null
          : FloatingActionButton(
              onPressed: () {
//                controller.animateTo(0,
//                    duration: Duration(seconds: 1), curve: Curves.bounceInOut);
                controller.jumpTo(33);
              },
              child: Icon(Icons.arrow_drop_up),
            ),
    );
  }
}
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