Flutter的可收缩面板ExpandPanel

import 'package:flutter/material.dart';

class ExpansionPanelItem {
  final String headerText;
  final Widget body;
  bool isExpanded;

  ExpansionPanelItem({
    this.headerText,
    this.body,
    this.isExpanded,
  });
}

class ExpansionPanelDemo extends StatefulWidget {
  @override
  _ExpansionPanelDemoState createState() => _ExpansionPanelDemoState();
}

class _ExpansionPanelDemoState extends State<ExpansionPanelDemo> {
  bool _isExpand = false;
  List<ExpansionPanelItem> _expansionPanelItems;

  @override
  void initState() {
    // TODO: implement initState
    super.initState();
    _expansionPanelItems = <ExpansionPanelItem>[
      ExpansionPanelItem(
          headerText: 'Panel A',
          body: Container(
            padding: EdgeInsets.all(16.0),
            width: double.infinity,
            child: Text('Content for Panel A'),
          ),
          isExpanded: false,
          ),
      ExpansionPanelItem(
          headerText: 'Panel B',
          body: Container(
            padding: EdgeInsets.all(16.0),
            width: double.infinity,
            child: Text('Content for Panel B'),
          ),
          isExpanded: false,
          ),
      ExpansionPanelItem(
          headerText: 'Panel C',
          body: Container(
            padding: EdgeInsets.all(16.0),
            width: double.infinity,
            child: Text('Content for Panel C'),
          ),
          isExpanded: false,
          )
    ];
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text('ExpansionPanelDemo'),
        elevation: 0.0,
      ),
      body: Container(
        padding: EdgeInsets.all(16.0),
        child: Column(
          mainAxisAlignment: MainAxisAlignment.center,
          children: <Widget>[
            ExpansionPanelList(
              expansionCallback: (panelIndex, isExpanded) {
                setState(() {
                  _expansionPanelItems[panelIndex].isExpanded =
                      !_expansionPanelItems[panelIndex].isExpanded;
                });
              },
              children: _expansionPanelItems.map((ExpansionPanelItem item) {
                return ExpansionPanel(
                    isExpanded: item.isExpanded,
                    body: item.body,
                    headerBuilder: (BuildContext context, bool isExpanded) {
                      return Container(
                        padding: EdgeInsets.all(16.0),
                        child: Text(
                          item.headerText,
                          style: Theme.of(context).textTheme.title,
                        ),
                      );
                    });
              }).toList(),
            ),
          ],
        ),
      ),
    );
  }
}