Flutter初探--半自定义ExpansionTile

背景

做移动端开发的朋友经常会遇到数据需要层级展示的场景，如二级或者三级列表。因此flutter也为我们提供了列表中可用来折叠的组件ExpansionTile，基本能满足我们的需求，但是...这玩意可自定义程度真的有限！用 ExpansionTile实现效果如下图所示：

未展开的效果图

展开的效果图

存在问题：
1.ExpansionTile背景色展开后才显示
2.上下分割线展开后才显示
3.分割线颜色不可修改
4.标题和图标展开时展示成了主题色

那如何解决这些问题呢？先看源码再说~

源码解析

const ExpansionTile({
    Key key,
    this.leading,
    @required this.title,
    this.backgroundColor,
    this.onExpansionChanged,
    this.children = const [],
    this.trailing,
    this.initiallyExpanded = false,
  }) : assert(initiallyExpanded != null),
       super(key: key);

leading:左侧头部组件，如用户头像
title:常见标题组件
backgroundColor:展开时子列表背景色
children:展开的widgets
trailing:用于替换尾部箭头的组件
initiallyExpanded:设置默认是否展开

可以看到，ExpansionTile提供的属性非常有限，并没有提供我们用于解决上边问题的方法，ExpansionTile中的代码并不多，其中定义了各种动画，并设置了动画区间，ExpansionTile的展示效果也都依赖于这些颜色~

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

  AnimationController _controller;
  Animation _iconTurns;
  Animation _heightFactor;
  Animation _borderColor;
  Animation _headerColor;
  Animation _iconColor;
  Animation _backgroundColor;

_ExpansionTileState中定义的各种动画

@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();
  }

复写didChangeDependencies来设置颜色区间，所以看到这里，我们需要做的只是拷贝一份出来，修改这里的颜色区间逻辑而已~

完整代码

import 'package:flutter/material.dart';

// import 'colors.dart';
// import 'icons.dart';
// import 'list_tile.dart';
// import 'theme.dart';
// import 'theme_data.dart';

const Duration _kExpand = Duration(milliseconds: 200);

/// A single-line [ListTile] with a trailing button that expands or collapses
/// the tile to reveal or hide the [children].
///
/// This widget is typically used with [ListView] to create an
/// "expand / collapse" list entry. When used with scrolling widgets like
/// [ListView], a unique [PageStorageKey] must be specified to enable the
/// [HJExpansionTile] to save and restore its expanded state when it is scrolled
/// in and out of view.
///
/// See also:
///
///  * [ListTile], useful for creating expansion tile [children] when the
///    expansion tile represents a sublist.
///  * The "Expand/collapse" section of
///    .

// 分割线显示时机
enum DividerDisplayTime {
  always, //总是显示
  opened, //展开时显示
  closed, //关闭时显示
  never //不显示
}

class HJExpansionTile extends StatefulWidget {
  /// Creates a single-line [ListTile] with a trailing button that expands or collapses
  /// the tile to reveal or hide the [children]. The [initiallyExpanded] property must
  /// be non-null.
  const HJExpansionTile({
    Key key,
    this.leading,
    @required this.title,
    this.backgroundColor,
    this.dividerColor,
    this.iconColor,
    this.dividerDisplayTime,
    this.onExpansionChanged,
    this.children = const [],
    this.trailing,
    this.initiallyExpanded = false,
  })  : assert(initiallyExpanded != null),
        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;

  /// Called when the tile expands or collapses.
  ///
  /// When the tile starts expanding, this function is called with the value
  /// true. When the tile starts collapsing, this function is called with
  /// the value false.
  final ValueChanged onExpansionChanged;

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

  /// Specifies if the list tile is initially expanded (true) or collapsed (false, the default).
  final bool initiallyExpanded;

  final Color dividerColor;

  final DividerDisplayTime dividerDisplayTime;

  final Color iconColor;

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

class _HJExpansionTileState extends State
    with SingleTickerProviderStateMixin {
  static final Animatable _easeOutTween =
      CurveTween(curve: Curves.easeOut);
  static final Animatable _easeInTween =
      CurveTween(curve: Curves.easeIn);
  static final Animatable _halfTween =
      Tween(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 _iconTurns;
  Animation _heightFactor;
  Animation _borderColor;
  Animation _headerColor;
  Animation _iconColor;
  Animation _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 =
        PageStorage.of(context)?.readState(context) ?? widget.initiallyExpanded;
    if (_isExpanded) _controller.value = 1.0;
  }

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

  void _handleTap() {
    setState(() {
      _isExpanded = !_isExpanded;
      if (_isExpanded) {
        _controller.forward();
      } else {
        _controller.reverse().then((void value) {
          if (!mounted) return;
          setState(() {
            // Rebuild without widget.children.
          });
        });
      }
      PageStorage.of(context)?.writeState(context, _isExpanded);
    });
    if (widget.onExpansionChanged != null)
      widget.onExpansionChanged(_isExpanded);
  }

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

    return Container(
      decoration: BoxDecoration(
        color: _backgroundColor.value ?? Colors.transparent,
        border: Border(
          bottom: BorderSide(color: borderSideColor),
        ),
      ),
      child: Column(
        mainAxisSize: MainAxisSize.min,
        children: [
          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() {
    
    setupDidvierColorTween();

    setupIconColorTween();
    
    setupBackgroundColor();

    super.didChangeDependencies();
  }

  void setupDidvierColorTween() {
    final ThemeData theme = Theme.of(context);

    Color beginColor = this.widget.dividerColor ?? theme.dividerColor;
    Color endColor = beginColor;

    switch (widget.dividerDisplayTime) {
      case DividerDisplayTime.always:
        break;
      case DividerDisplayTime.opened:
        endColor = Colors.transparent;
        break;
      case DividerDisplayTime.closed:
        beginColor = Colors.transparent;
        break;
      case DividerDisplayTime.never:
        beginColor = Colors.transparent;
        endColor = Colors.transparent;
        break;
      default:
    }
    _borderColorTween
      ..begin = beginColor
      ..end = endColor;
  }

  void setupIconColorTween(){
    final ThemeData theme = Theme.of(context);

    Color beginColor = this.widget.iconColor ?? theme.unselectedWidgetColor;
    Color endColor = beginColor;

    _iconColorTween
      ..begin = beginColor
      ..end = endColor;
  }

  void setupBackgroundColor(){
    _backgroundColorTween
    ..begin = widget.backgroundColor
    ..end = widget.backgroundColor;
  }
  @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),
    );
  }
}

修改内容说明

代码拷出来以后，原先引入的文件会报错，只需将它们注释或删除，引入material.dart即可

import 'package:flutter/material.dart';

// import 'colors.dart';
// import 'icons.dart';
// import 'list_tile.dart';
// import 'theme.dart';
// import 'theme_data.dart';

然后扩展了三个属性，用来配置分割线和icon颜色，当然icon你也可以用trail来设置~

定义了分割线枚举来区分分割线的显示时机

// 分割线显示时机
enum DividerDisplayTime {
  always, //总是显示
  opened, //展开时显示
  closed, //关闭时显示
  never //不显示
}

扩展的三个属性

  final Color dividerColor;

  final DividerDisplayTime dividerDisplayTime;

  final Color iconColor;

调整后的初始化方法

const HJExpansionTile({
    Key key,
    this.leading,
    @required this.title,
    this.backgroundColor,
    this.dividerColor,
    this.iconColor,
    this.dividerDisplayTime,
    this.onExpansionChanged,
    this.children = const [],
    this.trailing,
    this.initiallyExpanded = false,
  })  : assert(initiallyExpanded != null),
        super(key: key);

调整背景色，分割线颜色，icon的动画颜色区间

@override
  void didChangeDependencies() {
    
    setupDidvierColorTween();

    setupIconColorTween();
    
    setupBackgroundColor();

    super.didChangeDependencies();
  }

  void setupDidvierColorTween() {
    final ThemeData theme = Theme.of(context);

    Color beginColor = this.widget.dividerColor ?? theme.dividerColor;
    Color endColor = beginColor;

    switch (widget.dividerDisplayTime) {
      case DividerDisplayTime.always:
        break;
      case DividerDisplayTime.opened:
        endColor = Colors.transparent;
        break;
      case DividerDisplayTime.closed:
        beginColor = Colors.transparent;
        break;
      case DividerDisplayTime.never:
        beginColor = Colors.transparent;
        endColor = Colors.transparent;
        break;
      default:
    }
    _borderColorTween
      ..begin = beginColor
      ..end = endColor;
  }

  void setupIconColorTween(){
    final ThemeData theme = Theme.of(context);

    Color beginColor = this.widget.iconColor ?? theme.unselectedWidgetColor;
    Color endColor = beginColor;

    _iconColorTween
      ..begin = beginColor
      ..end = endColor;
  }

  void setupBackgroundColor(){
    _backgroundColorTween
    ..begin = widget.backgroundColor
    ..end = widget.backgroundColor;
  }

我不想要上方的分割线，所以只留了一个~任性

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

    return Container(
      decoration: BoxDecoration(
        color: _backgroundColor.value ?? Colors.transparent,
        border: Border(
          bottom: BorderSide(color: borderSideColor),
        ),
      ),
...

至此已修改完成~

修改后效果

调用Demo

HJExpansionTile tile = HJExpansionTile(
        title: Text(e['title']),
        children: [_expandCell(e['values'])],
        backgroundColor: Color(0xFFF9FAFC),
        dividerColor: Color(0xFFE6E6E6),
        dividerDisplayTime: DividerDisplayTime.always, //默认
        iconColor: Colors.grey,
      );

12039186-cd78a2e213f586cf.png

12039186-e32b4e7933f8dbaa.png

结语

本篇文章是在开发总所遇问题的总觉，如有更加方案，欢迎留言讨论，学习道路永无止境，不断学习和总结才能进步~

Flutter初探--半自定义ExpansionTile

背景

源码解析

完整代码

修改内容说明

修改后效果

结语

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