ExpansionLayout.dart

/*
 * @author lsy
 * @date   2020/5/20
 **/
import 'package:flutter/material.dart';
import 'package:flutter/widgets.dart';
import 'package:flutter_svg/flutter_svg.dart';

const Duration _kExpand = Duration(milliseconds: 200);

class ExpansionLayout extends StatefulWidget {
  const ExpansionLayout({
    Key key,
    this.leading,
    @required this.title,
    this.subtitle,
    this.backgroundColor,
    this.onExpansionChanged,
    this.children = const <Widget>[],
    this.trailing,
    this.initiallyExpanded = false,
  })  : assert(initiallyExpanded != null),
        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;

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

class _ExpansionTileState extends State<ExpansionLayout>
    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 _backgroundColorTween = ColorTween();

  AnimationController _controller;
  Animation<double> _iconTurns;
  Animation<double> _heightFactor;
  Animation<Color> _borderColor;
  Animation<Color> _headerColor;
  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));
    _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?? Color(0xffe5e5e5);

    return Container(
      decoration: BoxDecoration(
//        color: _backgroundColor.value ?? Colors.transparent,
        border: Border(
          bottom: BorderSide(color: borderSideColor),
        ),
      ),
      child: Column(
        mainAxisSize: MainAxisSize.min,
        children: <Widget>[
          ListTileTheme.merge(
            contentPadding: EdgeInsets.only(),
            textColor: _headerColor.value,
            child: ListTile(
              onTap: _handleTap,
              leading: widget.leading,
              title: widget.title,
              subtitle: widget.subtitle,
              trailing: widget.trailing ??
                  RotationTransition(
                    turns: _iconTurns,
                    child: Container(
                      width: 15,
                      height: 16,
                      child: SvgPicture.asset("images/bottom_arrow_black.svg"),
                    ),
                  ),
            ),
          ),
          ClipRect(
            child: Align(
              heightFactor: _heightFactor.value,
              child: child,
            ),
          ),
        ],
      ),
    );
  }

  @override
  void didChangeDependencies() {
    final ThemeData theme = Theme.of(context);
    _borderColorTween.begin=Color(0xffe5e5e5);
    _borderColorTween.end = Colors.transparent;
    _headerColorTween
      ..begin = theme.textTheme.subtitle1.color
      ..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),
    );
  }
}