如何在expansionPanelList - Flutter中全部展开或全部折叠

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('ExpansionPanelList Demo')),
        body: ExpansionPanelDemo(),
      ),
    );
  }
}

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

class _ExpansionPanelDemoState extends State<ExpansionPanelDemo> {
  List<ExpansionPanel> panels = [
    ExpansionPanel(headerValue: 'Panel 1', isExpanded: false),
    ExpansionPanel(headerValue: 'Panel 2', isExpanded: false),
    ExpansionPanel(headerValue: 'Panel 3', isExpanded: false),
  ];

  void _toggleAllPanels() {
    setState(() {
      panels.forEach((panel) => panel.isExpanded = !panels.every((p) => p.isExpanded));
    });
  }

  @override
  Widget build(BuildContext context) {
    return Column(
      children: [
        ElevatedButton(
          onPressed: _toggleAllPanels,
          child: Text('Toggle All Panels'),
        ),
        ListView.builder(
          itemCount: panels.length,
          itemBuilder: (context, index) {
            return ExpansionPanel(
              key: ValueKey(index),
              headerValue: panels[index].headerValue,
              isExpanded: panels[index].isExpanded,
              onExpansionChanged: (expanded) {
                setState(() {
                  panels[index].isExpanded = expanded;
                });
              },
              body: ListTile(title: Text('Content of ${panels[index].headerValue}')),
            );
          },
        ),
      ],
    );
  }
}

class ExpansionPanel extends StatelessWidget {
  final String headerValue;
  final bool isExpanded;
  final Function(bool) onExpansionChanged;

  ExpansionPanel({
    required this.headerValue,
    required this.isExpanded,
    required this.onExpansionChanged,
  });

  @override
  Widget build(BuildContext context) {
    return ListTile(
      title: Text(headerValue),
      trailing: Icon(isExpanded ? Icons.expand_less : Icons.expand_more),
      onTap: () {
        onExpansionChanged(!isExpanded);
      },
    );
  }
}