如何在扩展时更改ExpansionTile标题？

import 'package:flutter/material.dart';

void main() {
  runApp(MyApp());
}

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      home: Scaffold(
        appBar: AppBar(
          title: Text('ExpansionTile Example'),
        ),
        body: Center(
          child: ExpansionTileExample(),
        ),
      ),
    );
  }
}

class ExpansionTileExample extends StatefulWidget {
  @override
  _ExpansionTileExampleState createState() => _ExpansionTileExampleState();
}

class _ExpansionTileExampleState extends State<ExpansionTileExample> {
  bool _isExpanded = false;
  String _title = 'Click to expand';

  @override
  Widget build(BuildContext context) {
    return ExpansionTile(
      title: Text(_title),
      onExpansionChanged: (bool expanded) {
        setState(() {
          _isExpanded = expanded;
          _title = expanded ? 'Expanded' : 'Click to expand';
        });
      },
      children: <Widget>[
        ListTile(
          title: Text('Item 1'),
        ),
        ListTile(
          title: Text('Item 2'),
        ),
      ],
    );
  }
}