Widget _buildTiles(Entry root) {
? ? return new ExpansionTile(
? ? ? title: new Text(root.title),
? ? ? children: root.children.map(_buildTiles).toList(),
? ? );
? }

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

const Duration _kExpand = Duration(milliseconds: 200);

class ExpansionLayout extends StatefulWidget {
? const ExpansionLayout({
? ? Key key,
? ? this.backgroundColor,
? ? this.onExpansionChanged,
? ? this.children = const <Widget>[],
? ? this.trailing,
? ? this.isExpanded,
? }) : super(key: key);

? final ValueChanged<bool> onExpansionChanged;
? final List<Widget> children;

? final Color backgroundColor;
? //增加字段控制是否折疊
? final bool isExpanded;

? final Widget trailing;

? @override
? _ExpansionLayoutState createState() => _ExpansionLayoutState();
}

class _ExpansionLayoutState extends State<ExpansionLayout>
? ? with SingleTickerProviderStateMixin {
//折疊展開的動畫，主要是控制height
? static final Animatable<double> _easeInTween =
? ? ? CurveTween(curve: Curves.easeIn);
? AnimationController _controller;
? Animation<double> _heightFactor;

? bool _isExpanded;

? @override
? void initState() {
? ? super.initState();
? ? //初始化控制器以及出事狀態(tài)
? ? _controller = AnimationController(duration: _kExpand, vsync: this);
? ? _heightFactor = _controller.drive(_easeInTween);
? ? _isExpanded = widget.isExpanded;
? ? if (_isExpanded) _controller.value = 1.0;
? }

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

? void _handleTap() {
? ? setState(() {
? ? ? _isExpanded = widget.isExpanded;
? ? ? if (_isExpanded) {
? ? ? ? _controller.forward();
? ? ? } else {
? ? ? ? _controller.reverse().then<void>((void value) {
? ? ? ? ? if (!mounted) return;
? ? ? ? });
? ? ? }
? ? ? //保存頁面數(shù)據(jù)
? ? ? PageStorage.of(context)?.writeState(context, _isExpanded);
? ? });
? ? //回調(diào)展開事件
? ? if (widget.onExpansionChanged != null)
? ? ? widget.onExpansionChanged(_isExpanded);
? }

? Widget _buildChildren(BuildContext context, Widget child) {
? ? return Container(
? ? ? child: Column(
? ? ? ? mainAxisSize: MainAxisSize.min,
? ? ? ? children: <Widget>[
? ? ? ? ? ClipRect(
? ? ? ? ? ? child: Align(
? ? ? ? ? ? ? heightFactor: _heightFactor.value,
? ? ? ? ? ? ? child: child,
? ? ? ? ? ? ),
? ? ? ? ? ),
? ? ? ? ],
? ? ? ),
? ? );
? }

? @override
? Widget build(BuildContext context) {
? ? //執(zhí)行以下對應(yīng)的Tap事件
? ? _handleTap();
? ? final bool closed = !_isExpanded && _controller.isDismissed;
? ? return AnimatedBuilder(
? ? ? animation: _controller.view,
? ? ? builder: _buildChildren,
? ? ? child: closed ? null : Column(children: widget.children),
? ? );
? }
}