如何在Flutter中通过一个按钮使内容折叠？

import 'package:flutter/material.dart';

class MyWidget extends StatefulWidget {
  @override
  _MyWidgetState createState() => _MyWidgetState();
}

class _MyWidgetState extends State<MyWidget> {
  bool _isExpanded = false;

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text('折叠内容示例'),
      ),
      body: SingleChildScrollView(
        child: Container(
          padding: EdgeInsets.all(16.0),
          child: ExpansionPanelList(
            elevation: 1,
            expandedHeaderPadding: EdgeInsets.all(0),
            expansionCallback: (int index, bool isExpanded) {
              setState(() {
                _isExpanded = !isExpanded;
              });
            },
            children: [
              ExpansionPanel(
                headerBuilder: (BuildContext context, bool isExpanded) {
                  return ListTile(
                    title: Text('折叠内容'),
                  );
                },
                body: Container(
                  padding: EdgeInsets.all(16.0),
                  child: Text('这是折叠的内容'),
                ),
                isExpanded: _isExpanded,
              ),
            ],
          ),
        ),
      ),
    );
  }
}

void main() {
  runApp(MaterialApp(
    home: MyWidget(),
  ));
}