Flutter 在滚动 ListView 上显示和隐藏容器

Question

如何在向下滚动 ListView 时显示带有动画的 Container，并在向上滚动时隐藏它。

我附上的视频并不是我想要的确切实现，只是为了给你一个想法。

示例视频

https://imgur.com/a/auEzJQk

---

编辑：

每次向下滚动时，我都需要显示Container，每次向上滚动时，我都想隐藏它。它不应该依赖于ListView 的索引。

Answer 1

不确定我是否正确地回答了您的问题，这是您想要实现的目标吗？

截图：

---

代码：

class HomePage extends StatefulWidget {
  @override
  _HomePageState createState() => _HomePageState();
}

class _HomePageState extends State<HomePage> {
  // Height of your Container
  static final _containerHeight = 100.0;

  // You don't need to change any of these variables
  var _fromTop = -_containerHeight;
  var _controller = ScrollController();
  var _allowReverse = true, _allowForward = true;
  var _prevOffset = 0.0;
  var _prevForwardOffset = -_containerHeight;
  var _prevReverseOffset = 0.0;

  @override
  void initState() {
    super.initState();
    _controller.addListener(_listener);
  }

  // entire logic is inside this listener for ListView
  void _listener() {
    double offset = _controller.offset;
    var direction = _controller.position.userScrollDirection;

    if (direction == ScrollDirection.reverse) {
      _allowForward = true;
      if (_allowReverse) {
        _allowReverse = false;
        _prevOffset = offset;
        _prevForwardOffset = _fromTop;
      }

      var difference = offset - _prevOffset;
      _fromTop = _prevForwardOffset + difference;
      if (_fromTop > 0) _fromTop = 0;
    } else if (direction == ScrollDirection.forward) {
      _allowReverse = true;
      if (_allowForward) {
        _allowForward = false;
        _prevOffset = offset;
        _prevReverseOffset = _fromTop;
      }

      var difference = offset - _prevOffset;
      _fromTop = _prevReverseOffset + difference;
      if (_fromTop < -_containerHeight) _fromTop = -_containerHeight;
    }
    setState(() {}); // for simplicity I'm calling setState here, you can put bool values to only call setState when there is a genuine change in _fromTop
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(title: Text("ListView")),
      body: Stack(
        children: <Widget>[
          _yourListView(),
          Positioned(
            top: _fromTop,
            left: 0,
            right: 0,
            child: _yourContainer(),
          )
        ],
      ),
    );
  }

  Widget _yourListView() {
    return ListView.builder(
      itemCount: 100,
      controller: _controller,
      itemBuilder: (_, index) => ListTile(title: Text("Item $index")),
    );
  }

  Widget _yourContainer() {
    return Opacity(
      opacity: 1 - (-_fromTop / _containerHeight),
      child: Container(
        height: _containerHeight,
        color: Colors.red,
        alignment: Alignment.center,
        child: Text("Your Container", style: TextStyle(fontSize: 32, fontWeight: FontWeight.bold, color: Colors.white)),
      ),
    );
  }
}

Answer 2

import 'package:flutter/cupertino.dart';
import 'package:flutter/material.dart';

void main() => runApp(MyApp());

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    const double HEIGHT = 96;
    final ValueNotifier<double> notifier = ValueNotifier(0);
    return MaterialApp(
      debugShowCheckedModeBanner: false,
      home: Scaffold(
        appBar: AppBar(title: const Text('Test')),
        body: Stack(
          children: [
            NotificationListener<ScrollNotification>(
              onNotification: (n) {
                if (n.metrics.pixels <= HEIGHT) {
                  notifier.value = n.metrics.pixels;
                }
                return false;
              },
              child: ListView.builder(
                itemCount: 42,
                itemBuilder: (context, index) {
                  return Container(
                    height: 64,
                    padding: const EdgeInsets.all(16),
                    alignment: Alignment.centerLeft,
                    child: Text('Item $index'),
                  );
                },
              ),
            ),
            HideableWidget(height: HEIGHT, notifier: notifier),
          ],
        ),
      ),
    );
  }
}

class HideableWidget extends StatelessWidget {
  final double height;
  final ValueNotifier<double> notifier;

  HideableWidget({@required this.height, @required this.notifier});

  @override
  Widget build(BuildContext context) {
    return ValueListenableBuilder<double>(
      valueListenable: notifier,
      builder: (context, value, child) {
        return Transform.translate(
          offset: Offset(0, value - height),
          child: Container(
            height: 80,
            color: Colors.red,
          ),
        );
      },
    );
  }
}

Answer 3

我已经解决了您的问题。这是演示代码

 class _DemoState extends State<WidgetDemo> {
      ScrollController scrollController = new ScrollController();
      bool isVisible = true;

      @override
      initState() {
        super.initState();
        scrollController.addListener(() {
          if (scrollController.position.userScrollDirection ==
              ScrollDirection.reverse) {
            if (isVisible)
              setState(() {
                isVisible = false;
              });
          }
          if (scrollController.position.userScrollDirection ==
              ScrollDirection.forward) {
            if (!isVisible)
              setState(() {
                isVisible = true;
              });
          }
        });
      }

      @override
      Widget build(BuildContext context) {
        return Scaffold(
          body: Stack(
            children: <Widget>[
              new CustomScrollView(
                controller: scrollController,
                shrinkWrap: true,
                slivers: <Widget>[
                  new SliverPadding(
                    padding: const EdgeInsets.all(20.0),
                    sliver: new SliverList(
                      delegate: new SliverChildListDelegate(
                        <Widget>[
                          const Text('My temp data'),
                          const Text('Wow its working'),
                          const Text('My temp data'),
                          const Text('Wow its working'),
                          const Text('My temp data'),
                          const Text('Wow its working'),
                          const Text('My temp data'),
                          const Text('Wow its working'),
                          const Text('My temp data'),
                          const Text('Wow its working'),
                          const Text('My temp data'),
                          const Text('My temp data'),
                          const Text('Wow its working'),
                          const Text('My temp data'),
                          const Text('Wow its working'),
                          const Text('My temp data'),
                          const Text('Wow its working'),
                          const Text('My temp data'),
                          const Text('Wow its working'),
                          const Text('My temp data'),
                          const Text('Wow its working'),
                          const Text('My temp data'),
                          const Text('Wow its working'),
                          const Text('My temp data'),
                          const Text('Wow its working'),
                          const Text('My temp data'),
                          const Text('Wow its working'),
                          const Text('My temp data'),
                          const Text('Wow its working'),
                          const Text('My temp data'),
                          const Text('Wow its working'),
                          const Text('My temp data'),
                          const Text('Wow its working'),
                          const Text('My temp data'),
                          const Text('Wow its working'),
                          const Text('My temp data'),
                          const Text('Wow its working'),
                          const Text('My temp data'),
                          const Text('Wow its working'),
                          const Text('My temp data'),
                          const Text('Wow its working'),
                          const Text('My temp data'),
                          const Text('Wow its working'),
                          const Text('Wow its working'),
                          const Text('My temp data'),
                          const Text('Wow its working'),
                          const Text('My temp data'),
                          const Text('Wow its working'),
                        ],
                      ),
                    ),
                  ),
                ],
              ),
              AnimatedContainer(
                  duration: Duration(milliseconds: 400),
                  height: isVisible ? 60.0 : 0.0,
                  child: new Container(
                    color: Colors.green,
                    width: MediaQuery.of(context).size.width,
                    child: Center(child: Text("Container")),
                  )),
            ],
          ),
        );
      }
    }