Flutter 中有没有办法只允许扩展动态生成的 ListView 的一个 ExpansionTile？

Question

Flutter 中有没有办法只允许动态生成的 ListView 的一个 ExpansionTile 展开？

例如我的 ListView 有三个 ExpansionTiles，我单击第一个，它会展开。现在，如果我点击第二个，第二个应该会展开，而第一个应该会自行关闭。

在我看来，它应该像将这个任务放入“onExpansionChanged”方法一样工作，但我不知道如何。

Answer 1

你不能使用 Flutter 的 ExpansionTile，但我创建了一个 CustomExpansionTile 允许这样做：

CustomExpansionTile：

import 'package:flutter/material.dart';

const Duration _kExpand = Duration(milliseconds: 200);

class CustomExpansionTile extends StatefulWidget {

  const CustomExpansionTile({
    Key key,
    this.leading,
    @required this.title,
    this.backgroundColor,
    this.children = const <Widget>[],
    this.trailing,
    @required this.expandedItem,
  }) :  super(key: key);

  /// A widget to display before the title.
  ///
  /// Typically a [CircleAvatar] widget.
  final Widget leading;

  /// The primary content of the list item.
  ///
  /// Typically a [Text] widget.
  final Widget title;

  /// The widgets that are displayed when the tile expands.
  ///
  /// Typically [ListTile] widgets.
  final List<Widget> children;

  /// The color to display behind the sublist when expanded.
  final Color backgroundColor;

  /// A widget to display instead of a rotating arrow icon.
  final Widget trailing;

  final ValueNotifier<Key> expandedItem;

  @override
  _CustomExpansionTileState createState() => _CustomExpansionTileState();
}

class _CustomExpansionTileState extends State<CustomExpansionTile> with SingleTickerProviderStateMixin {
  static final Animatable<double> _easeOutTween = CurveTween(curve: Curves.easeOut);
  static final Animatable<double> _easeInTween = CurveTween(curve: Curves.easeIn);
  static final Animatable<double> _halfTween = Tween<double>(begin: 0.0, end: 0.5);

  final ColorTween _borderColorTween = ColorTween();
  final ColorTween _headerColorTween = ColorTween();
  final ColorTween _iconColorTween = ColorTween();
  final ColorTween _backgroundColorTween = ColorTween();

  AnimationController _controller;
  Animation<double> _iconTurns;
  Animation<double> _heightFactor;
  Animation<Color> _borderColor;
  Animation<Color> _headerColor;
  Animation<Color> _iconColor;
  Animation<Color> _backgroundColor;

  bool _isExpanded = false;

  @override
  void initState() {
    super.initState();
    _controller = AnimationController(duration: _kExpand, vsync: this);
    _heightFactor = _controller.drive(_easeInTween);
    _iconTurns = _controller.drive(_halfTween.chain(_easeInTween));
    _borderColor = _controller.drive(_borderColorTween.chain(_easeOutTween));
    _headerColor = _controller.drive(_headerColorTween.chain(_easeInTween));
    _iconColor = _controller.drive(_iconColorTween.chain(_easeInTween));
    _backgroundColor = _controller.drive(_backgroundColorTween.chain(_easeOutTween));

    _isExpanded =  widget.expandedItem.value == widget.key;
    if (_isExpanded)
      _controller.value = 1.0;

    widget.expandedItem.addListener(listener);
  }

  void listener() {
    setState(() {
      _changeState(widget.expandedItem.value == widget.key);
    });
  }

  @override
  void dispose() {
    _controller.dispose();
    widget.expandedItem.removeListener(listener);
    super.dispose();
  }

  void _changeState(bool isExpanded) {
    setState(() {
      _isExpanded = isExpanded;
      if (_isExpanded) {
        _controller.forward();
      } else {
        _controller.reverse().then<void>((void value) {
          if (!mounted)
            return;
          setState(() {
            // Rebuild without widget.children.
          });
        });
      }
      PageStorage.of(context)?.writeState(context, _isExpanded);
    });
  }

  void _handleTap() {
    _changeState(!_isExpanded);
    widget.expandedItem.value = _isExpanded ? widget.key : null;
  }

  Widget _buildChildren(BuildContext context, Widget child) {
    final Color borderSideColor = _borderColor.value ?? Colors.transparent;

    return Container(
      decoration: BoxDecoration(
        color: _backgroundColor.value ?? Colors.transparent,
        border: Border(
          top: BorderSide(color: borderSideColor),
          bottom: BorderSide(color: borderSideColor),
        ),
      ),
      child: Column(
        mainAxisSize: MainAxisSize.min,
        children: <Widget>[
          ListTileTheme.merge(
            iconColor: _iconColor.value,
            textColor: _headerColor.value,
            child: ListTile(
              onTap: _handleTap,
              leading: widget.leading,
              title: widget.title,
              trailing: widget.trailing ?? RotationTransition(
                turns: _iconTurns,
                child: const Icon(Icons.expand_more),
              ),
            ),
          ),
          ClipRect(
            child: Align(
              heightFactor: _heightFactor.value,
              child: child,
            ),
          ),
        ],
      ),
    );
  }

  @override
  void didChangeDependencies() {
    final ThemeData theme = Theme.of(context);
    _borderColorTween
      ..end = theme.dividerColor;
    _headerColorTween
      ..begin = theme.textTheme.subhead.color
      ..end = theme.accentColor;
    _iconColorTween
      ..begin = theme.unselectedWidgetColor
      ..end = theme.accentColor;
    _backgroundColorTween
      ..end = widget.backgroundColor;
    super.didChangeDependencies();
  }

  @override
  Widget build(BuildContext context) {
    final bool closed = !_isExpanded && _controller.isDismissed;
    return AnimatedBuilder(
      animation: _controller.view,
      builder: _buildChildren,
      child: closed ? null : Column(children: widget.children),
    );

  }

}

用法：

import 'dart:async';

import 'package:flutter/material.dart';
import 'package:playground/custom_expansion_tile.dart';

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

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Flutter Demo',
      theme: ThemeData(
        primarySwatch: Colors.blue,
      ),
      home: MyHomePage(title: 'Flutter Demo Home Page'),
    );
  }
}

class MyHomePage extends StatefulWidget {
  MyHomePage({Key key, this.title}) : super(key: key);

  final String title;

  @override
  _MyHomePageState createState() => _MyHomePageState();
}



class _MyHomePageState extends State<MyHomePage> {
  ValueNotifier<Key> _expanded = ValueNotifier(null);

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text(widget.title),
      ),
      body: ListView(
        children: <Widget>[
          CustomExpansionTile(
            expandedItem: _expanded,
            key: Key('1'),
            title: Text('Title #1'),
            children: <Widget>[
              Text('Child')
            ],
          ),
          CustomExpansionTile(
            expandedItem: _expanded,
            key: Key('2'),
            title: Text('Title #2'),
            children: <Widget>[
              Text('Child')
            ],

          ),
          CustomExpansionTile(
            expandedItem: _expanded,
            key: Key('3'),
            title: Text('Title #3'),
            children: <Widget>[
              Text('Child')
            ],

          )
        ],
      ),
    );
  }
}

注意：您必须为 CustomExpansionTiles 提供唯一的密钥才能使其工作