覆盖自定义 flutter 小部件

Question

I have a short question. I want to override ExpansionTile with adding another row (Below leading, title/subtitle, trailing). So do I have to copy whole implementation of this widget to my custom one and there add this new row? Or can I just override it somehow with just this one line?

Base one:

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

const Duration _kExpand = Duration(milliseconds: 200);

class ExpansionTile extends StatefulWidget {
  const ExpansionTile({
    Key key,
    this.leading,
    @required this.title,
    this.subtitle,
    this.backgroundColor,
    this.onExpansionChanged,
    this.children = const <Widget>[],
    this.trailing,
    this.initiallyExpanded = false,
    this.maintainState = false,
    this.tilePadding,
    this.expandedCrossAxisAlignment,
    this.expandedAlignment,
    this.childrenPadding,
  })  : assert(initiallyExpanded != null),
        assert(maintainState != null),
        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.',
        ),
        super(key: key);

  final Widget leading;
  final Widget title;
  final Widget subtitle;
  final ValueChanged<bool> onExpansionChanged;
  final List<Widget> children;
  final Color backgroundColor;
  final Widget trailing;
  final bool initiallyExpanded;
  final bool maintainState;
  final EdgeInsetsGeometry tilePadding;
  final Alignment expandedAlignment;
  final CrossAxisAlignment expandedCrossAxisAlignment;
  final EdgeInsetsGeometry childrenPadding;

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

class _ExpansionTileState extends State<ExpansionTile>
    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 = PageStorage.of(context)?.readState(context) as bool ??
        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>((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(
          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,
              contentPadding: widget.tilePadding,
              leading: widget.leading,
              title: widget.title,
              subtitle: widget.subtitle,
              trailing: widget.trailing ??
                  RotationTransition(
                    turns: _iconTurns,
                    child: const Icon(Icons.expand_more),
                  ),
            ),
          ),
          ClipRect(
            child: Align(
              alignment: widget.expandedAlignment ?? Alignment.center,
              heightFactor: _heightFactor.value,
              child: child,
            ),
          ),
        ],
      ),
    );
  }

  @override
  void didChangeDependencies() {
    final ThemeData theme = Theme.of(context);
    _borderColorTween.end = theme.dividerColor;
    _headerColorTween
      ..begin = theme.textTheme.subtitle1.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;
    final bool shouldRemoveChildren = closed && !widget.maintainState;

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

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

There's a lot of code and I don't want to change anything more despite add one Row.

Also i need to get rid off custom grey lines (I am using divider do separate tiles)

Answer 1

You can just wrap the ListTile in a Column for another Row or any other widgets:

Column(
        children: [
          ListTile(
            leading: Icon(Icons.circle),
            title: Text('Title'),
            subtitle: Text('subtitle'),
            trailing: Icon(Icons.more_vert),
            visualDensity: VisualDensity.compact,
          ),
          Placeholder(fallbackHeight: 10.0) //place your widget/row here
        ],
      )