从扩展图块中删除尾随图标和为尾随图标分配的空间

Question

我正在使用扩展图块，但我不想在小部件的末尾占用任何尾部空间。尽管我删除了带有大小框的尾随图标，但图标的空间仍然被占用，我不想要内容的整个空间，而不是尾随图标。

下面是我的代码：

ExpansionTile(
      initiallyExpanded: expanded,
      trailing: const SizedBox.shrink(),
      textColor: Colors.teal,
      collapsedTextColor: Colors.teal,
      title: SingleChildScrollView(
          scrollDirection: Axis.horizontal,
          child: Center(
              child: Text(title,
                  style: const TextStyle(
                    color: Colors.teal,
                  )))),
      iconColor: Colors.green,
      collapsedIconColor: Colors.teal,
      children: body)

下图：

Answer 1

我找到了解决这个问题的方法。您所要做的就是转到 ExpansionTile Widget 并复制它。创建一个新文件并将小部件名称编辑为您想要的名称。然后从其中的 ListTile Widget 中删除尾随属性。中提琴！！！您得到了一个没有尾随间隙的 ExpansionTile 小部件。我会附上一个例子。

感谢Satheesh Kumar提出了这个绝妙的想法

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

const Duration _kExpand = Duration(milliseconds: 200);

class ExpansionTileController {
  ExpansionTileController();

  _MyExpansionTileState? _state;

  bool get isExpanded {
    assert(_state != null, 'line 14');
    return _state!._isExpanded;
  }

  void expand() {
    assert(_state != null, 'line 19');
    if (!isExpanded) {
      _state!._toggleExpansion();
    }
  }

  void collapse() {
    assert(_state != null, 'line 27');
    if (isExpanded) {
      _state!._toggleExpansion();
    }
  }

  static ExpansionTileController of(BuildContext context) {
    final result = context.findAncestorStateOfType<_MyExpansionTileState>();
    if (result != null) {
      return result._tileController;
    }
    throw FlutterError.fromParts(<DiagnosticsNode>[
      ErrorSummary(
        'ExpansionTileController.of() called with a context that does not contain a ExpansionTile.',
      ),
      ErrorDescription(
        'No ExpansionTile ancestor could be found starting from the context that was passed to ExpansionTileController.of(). '
        'This usually happens when the context provided is from the same StatefulWidget as that '
        'whose build function actually creates the ExpansionTile widget being sought.',
      ),
      ErrorHint(
        'There are several ways to avoid this problem. The simplest is to use a Builder to get a '
        'context that is "under" the ExpansionTile. For an example of this, please see the '
        'documentation for ExpansionTileController.of():\n'
        '  https://api.flutter.dev/flutter/material/ExpansionTile/of.html',
      ),
      ErrorHint(
        'A more efficient solution is to split your build function into several widgets. This '
        'introduces a new context from which you can obtain the ExpansionTile. In this solution, '
        'you would have an outer widget that creates the ExpansionTile populated by instances of '
        'your new inner widgets, and then in these inner widgets you would use ExpansionTileController.of().\n'
        'An other solution is assign a GlobalKey to the ExpansionTile, '
        'then use the key.currentState property to obtain the ExpansionTile rather than '
        'using the ExpansionTileController.of() function.',
      ),
      context.describeElement('The context used was'),
    ]);
  }

  static ExpansionTileController? maybeOf(BuildContext context) {
    return context
        .findAncestorStateOfType<_MyExpansionTileState>()
        ?._tileController;
  }
}

class MyExpansionTile extends StatefulWidget {
  const MyExpansionTile({
    required this.title,
    super.key,
    this.leading,
    this.subtitle,
    this.onExpansionChanged,
    this.children = const <Widget>[],
    this.initiallyExpanded = false,
    this.maintainState = false,
    this.tilePadding,
    this.expandedCrossAxisAlignment,
    this.expandedAlignment,
    this.childrenPadding,
    this.backgroundColor,
    this.collapsedBackgroundColor,
    this.textColor,
    this.collapsedTextColor,
    this.iconColor,
    this.collapsedIconColor,
    this.shape,
    this.collapsedShape,
    this.clipBehavior,
    this.controlAffinity,
    this.controller,
    this.dense,
    this.visualDensity,
    this.enableFeedback = true,
    this.enabled = true,
    this.expansionAnimationStyle,
  }) : assert(
          expandedCrossAxisAlignment != CrossAxisAlignment.baseline,
          'CrossAxisAlignment.baseline is not supported since the expanded children '
          'are aligned in a column, not a row. Try to use another constant.',
        );

  final Widget? leading;
  final Widget title;
  final Widget? subtitle;
  final ValueChanged<bool>? onExpansionChanged;
  final List<Widget> children;
  final Color? backgroundColor;
  final Color? collapsedBackgroundColor;
  final bool initiallyExpanded;
  final bool maintainState;
  final EdgeInsetsGeometry? tilePadding;
  final Alignment? expandedAlignment;
  final CrossAxisAlignment? expandedCrossAxisAlignment;
  final EdgeInsetsGeometry? childrenPadding;
  final Color? iconColor;
  final Color? collapsedIconColor;
  final Color? textColor;
  final Color? collapsedTextColor;
  final ShapeBorder? shape;
  final ShapeBorder? collapsedShape;
  final Clip? clipBehavior;
  final ListTileControlAffinity? controlAffinity;
  final ExpansionTileController? controller;
  final bool? dense;
  final VisualDensity? visualDensity;
  final bool? enableFeedback;
  final bool enabled;
  final AnimationStyle? expansionAnimationStyle;

  @override
  State<MyExpansionTile> createState() => _MyExpansionTileState();
}

class _MyExpansionTileState extends State<MyExpansionTile>
    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, end: 0.5);

  final ShapeBorderTween _borderTween = ShapeBorderTween();
  final ColorTween _headerColorTween = ColorTween();
  final ColorTween _iconColorTween = ColorTween();
  final ColorTween _backgroundColorTween = ColorTween();
  final CurveTween _heightFactorTween = CurveTween(curve: Curves.easeIn);

  late AnimationController _animationController;
  late Animation<double> _iconTurns;
  late Animation<double> _heightFactor;
  late Animation<ShapeBorder?> _border;
  late Animation<Color?> _headerColor;
  late Animation<Color?> _iconColor;
  late Animation<Color?> _backgroundColor;

  bool _isExpanded = false;
  late ExpansionTileController _tileController;

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

    _isExpanded = PageStorage.maybeOf(context)?.readState(context) as bool? ??
        widget.initiallyExpanded;
    if (_isExpanded) {
      _animationController.value = 1.0;
    }

    assert(widget.controller?._state == null, 'line 190');
    _tileController = widget.controller ?? ExpansionTileController();
    _tileController._state = this;
  }

  @override
  void dispose() {
    _tileController._state = null;
    _animationController.dispose();
    super.dispose();
  }

  void _toggleExpansion() {
    final textDirection = WidgetsLocalizations.of(context).textDirection;
    final localizations = MaterialLocalizations.of(context);
    final stateHint =
        _isExpanded ? localizations.expandedHint : localizations.collapsedHint;
    setState(() {
      _isExpanded = !_isExpanded;
      if (_isExpanded) {
        _animationController.forward();
      } else {
        _animationController.reverse().then<void>((void value) {
          if (!mounted) {
            return;
          }
          setState(() {});
        });
      }
      PageStorage.maybeOf(context)?.writeState(context, _isExpanded);
    });
    widget.onExpansionChanged?.call(_isExpanded);
    SemanticsService.announce(stateHint, textDirection);
  }

  void _handleTap() {
    _toggleExpansion();
  }

  ListTileControlAffinity _effectiveAffinity(
    ListTileControlAffinity? affinity,
  ) {
    switch (affinity ?? ListTileControlAffinity.trailing) {
      case ListTileControlAffinity.leading:
        return ListTileControlAffinity.leading;
      case ListTileControlAffinity.trailing:
      case ListTileControlAffinity.platform:
        return ListTileControlAffinity.trailing;
    }
  }

  Widget? _buildIcon(BuildContext context) {
    return RotationTransition(
      turns: _iconTurns,
      child: const Icon(Icons.expand_more),
    );
  }

  Widget? _buildLeadingIcon(BuildContext context) {
    if (_effectiveAffinity(widget.controlAffinity) !=
        ListTileControlAffinity.leading) {
      return null;
    }
    return _buildIcon(context);
  }

  Widget _buildChildren(BuildContext context, Widget? child) {
    final theme = Theme.of(context);
    final expansionTileTheme = ExpansionTileTheme.of(context);
    final expansionTileBorder = _border.value ??
        const Border(
          top: BorderSide(color: Colors.transparent),
          bottom: BorderSide(color: Colors.transparent),
        );
    final clipBehavior =
        widget.clipBehavior ?? expansionTileTheme.clipBehavior ?? Clip.none;
    final localizations = MaterialLocalizations.of(context);
    final onTapHint = _isExpanded
        ? localizations.expansionTileExpandedTapHint
        : localizations.expansionTileCollapsedTapHint;
    String? semanticsHint;
    switch (theme.platform) {
      case TargetPlatform.iOS:
      case TargetPlatform.macOS:
        semanticsHint = _isExpanded
            ? '${localizations.collapsedHint}\n ${localizations.expansionTileExpandedHint}'
            : '${localizations.expandedHint}\n ${localizations.expansionTileCollapsedHint}';
      case TargetPlatform.android:
      case TargetPlatform.fuchsia:
      case TargetPlatform.linux:
      case TargetPlatform.windows:
        break;
    }

    return Container(
      clipBehavior: clipBehavior,
      decoration: ShapeDecoration(
        color: _backgroundColor.value ??
            expansionTileTheme.backgroundColor ??
            Colors.transparent,
        shape: expansionTileBorder,
      ),
      child: Column(
        mainAxisSize: MainAxisSize.min,
        children: <Widget>[
          Semantics(
            hint: semanticsHint,
            onTapHint: onTapHint,
            child: ListTileTheme.merge(
              iconColor: _iconColor.value ?? expansionTileTheme.iconColor,
              textColor: _headerColor.value,
              child: ListTile(
                enabled: widget.enabled,
                onTap: _handleTap,
                dense: widget.dense,
                visualDensity: widget.visualDensity,
                enableFeedback: widget.enableFeedback,
                contentPadding:
                    widget.tilePadding ?? expansionTileTheme.tilePadding,
                leading: widget.leading ?? _buildLeadingIcon(context),
                title: widget.title,
                subtitle: widget.subtitle,
              ),
            ),
          ),
          ClipRect(
            child: Align(
              alignment: widget.expandedAlignment ??
                  expansionTileTheme.expandedAlignment ??
                  Alignment.center,
              heightFactor: _heightFactor.value,
              child: child,
            ),
          ),
        ],
      ),
    );
  }

  @override
  void didUpdateWidget(covariant MyExpansionTile oldWidget) {
    super.didUpdateWidget(oldWidget);
    final theme = Theme.of(context);
    final expansionTileTheme = ExpansionTileTheme.of(context);
    final defaults = theme.useMaterial3
        ? _ExpansionTileDefaultsM3(context)
        : _ExpansionTileDefaultsM2(context);
    if (widget.collapsedShape != oldWidget.collapsedShape ||
        widget.shape != oldWidget.shape) {
      _updateShapeBorder(expansionTileTheme, theme);
    }
    if (widget.collapsedTextColor != oldWidget.collapsedTextColor ||
        widget.textColor != oldWidget.textColor) {
      _updateHeaderColor(expansionTileTheme, defaults);
    }
    if (widget.collapsedIconColor != oldWidget.collapsedIconColor ||
        widget.iconColor != oldWidget.iconColor) {
      _updateIconColor(expansionTileTheme, defaults);
    }
    if (widget.backgroundColor != oldWidget.backgroundColor ||
        widget.collapsedBackgroundColor != oldWidget.collapsedBackgroundColor) {
      _updateBackgroundColor(expansionTileTheme);
    }
    if (widget.expansionAnimationStyle != oldWidget.expansionAnimationStyle) {
      _updateAnimationDuration(expansionTileTheme);
      _updateHeightFactorCurve(expansionTileTheme);
    }
  }

  @override
  void didChangeDependencies() {
    final theme = Theme.of(context);
    final expansionTileTheme = ExpansionTileTheme.of(context);
    final defaults = theme.useMaterial3
        ? _ExpansionTileDefaultsM3(context)
        : _ExpansionTileDefaultsM2(context);
    _updateAnimationDuration(expansionTileTheme);
    _updateShapeBorder(expansionTileTheme, theme);
    _updateHeaderColor(expansionTileTheme, defaults);
    _updateIconColor(expansionTileTheme, defaults);
    _updateBackgroundColor(expansionTileTheme);
    _updateHeightFactorCurve(expansionTileTheme);
    super.didChangeDependencies();
  }

  void _updateAnimationDuration(ExpansionTileThemeData expansionTileTheme) {
    _animationController.duration = widget.expansionAnimationStyle?.duration ??
        expansionTileTheme.expansionAnimationStyle?.duration ??
        _kExpand;
  }

  void _updateShapeBorder(
    ExpansionTileThemeData expansionTileTheme,
    ThemeData theme,
  ) {
    _borderTween
      ..begin = widget.collapsedShape ??
          expansionTileTheme.collapsedShape ??
          const Border(
            top: BorderSide(color: Colors.transparent),
            bottom: BorderSide(color: Colors.transparent),
          )
      ..end = widget.shape ??
          expansionTileTheme.shape ??
          Border(
            top: BorderSide(color: theme.dividerColor),
            bottom: BorderSide(color: theme.dividerColor),
          );
  }

  void _updateHeaderColor(
    ExpansionTileThemeData expansionTileTheme,
    ExpansionTileThemeData defaults,
  ) {
    _headerColorTween
      ..begin = widget.collapsedTextColor ??
          expansionTileTheme.collapsedTextColor ??
          defaults.collapsedTextColor
      ..end = widget.textColor ??
          expansionTileTheme.textColor ??
          defaults.textColor;
  }

  void _updateIconColor(
    ExpansionTileThemeData expansionTileTheme,
    ExpansionTileThemeData defaults,
  ) {
    _iconColorTween
      ..begin = widget.collapsedIconColor ??
          expansionTileTheme.collapsedIconColor ??
          defaults.collapsedIconColor
      ..end = widget.iconColor ??
          expansionTileTheme.iconColor ??
          defaults.iconColor;
  }

  void _updateBackgroundColor(ExpansionTileThemeData expansionTileTheme) {
    _backgroundColorTween
      ..begin = widget.collapsedBackgroundColor ??
          expansionTileTheme.collapsedBackgroundColor
      ..end = widget.backgroundColor ?? expansionTileTheme.backgroundColor;
  }

  void _updateHeightFactorCurve(ExpansionTileThemeData expansionTileTheme) {
    _heightFactorTween.curve = widget.expansionAnimationStyle?.curve ??
        expansionTileTheme.expansionAnimationStyle?.curve ??
        Curves.easeIn;
  }

  @override
  Widget build(BuildContext context) {
    final expansionTileTheme = ExpansionTileTheme.of(context);
    final closed = !_isExpanded && _animationController.isDismissed;
    final shouldRemoveChildren = closed && !widget.maintainState;

    final Widget result = Offstage(
      offstage: closed,
      child: TickerMode(
        enabled: !closed,
        child: Padding(
          padding: widget.childrenPadding ??
              expansionTileTheme.childrenPadding ??
              EdgeInsets.zero,
          child: Column(
            crossAxisAlignment:
                widget.expandedCrossAxisAlignment ?? CrossAxisAlignment.center,
            children: widget.children,
          ),
        ),
      ),
    );

    return AnimatedBuilder(
      animation: _animationController.view,
      builder: _buildChildren,
      child: shouldRemoveChildren ? null : result,
    );
  }
}

class _ExpansionTileDefaultsM2 extends ExpansionTileThemeData {
  _ExpansionTileDefaultsM2(this.context);

  final BuildContext context;
  late final ThemeData _theme = Theme.of(context);
  late final ColorScheme _colorScheme = _theme.colorScheme;

  @override
  Color? get textColor => _colorScheme.primary;

  @override
  Color? get iconColor => _colorScheme.primary;

  @override
  Color? get collapsedTextColor => _theme.textTheme.titleMedium!.color;

  @override
  Color? get collapsedIconColor => _theme.unselectedWidgetColor;
}

class _ExpansionTileDefaultsM3 extends ExpansionTileThemeData {
  _ExpansionTileDefaultsM3(this.context);

  final BuildContext context;
  late final ThemeData _theme = Theme.of(context);
  late final ColorScheme _colors = _theme.colorScheme;

  @override
  Color? get textColor => _colors.onSurface;

  @override
  Color? get iconColor => _colors.primary;

  @override
  Color? get collapsedTextColor => _colors.onSurface;

  @override
  Color? get collapsedIconColor => _colors.onSurfaceVariant;
}

Answer 2

根据您想要的行为，您可以只使用 ListTile:

ListTile(
      trailing: const SizedBox.shrink(),
      textColor: Colors.teal,
      title: SingleChildScrollView(
          scrollDirection: Axis.horizontal,
          child: Center(
              child: Text(title,
                  style: const TextStyle(
                    color: Colors.teal,
                  )
               )
            )
      ),
      children: body)

注意：如果 ListTile 位于行/列中，您可能需要将其包装在扩展小部件中