Expansion panel - single expanded

main.dart

import 'package:flutter/material.dart';

void main() => runApp(const MyApp());

class MyApp extends StatelessWidget {
  const MyApp({Key? key}) : super(key: key);

  static const String _title = 'Flutter Code Sample';

  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: _title,
      home: Scaffold(
        appBar: AppBar(title: const Text(_title)),
        body: const MyStatefulWidget(),
      ),
    );
  }
}

// stores ExpansionPanel state information
class Item {
  Item({
    required this.expandedValue,
    required this.headerValue,
    this.isExpanded = false,
  });

  String expandedValue;
  String headerValue;
  bool isExpanded;
}

List<Item> generateItems(int numberOfItems) {
  return List<Item>.generate(numberOfItems, (int index) {
    return Item(
      headerValue: 'Panel $index',
      expandedValue: 'This is item number $index',
    );
  });
}

class MyStatefulWidget extends StatefulWidget {
  const MyStatefulWidget({Key? key}) : super(key: key);

  @override
  State<MyStatefulWidget> createState() => _MyStatefulWidgetState();
}

class _MyStatefulWidgetState extends State<MyStatefulWidget> {
  final List<Item> _data = generateItems(8);

  @override
  Widget build(BuildContext context) {
    return SingleChildScrollView(
      child: Container(
        child: _buildPanel(),
      ),
    );
  }

  Widget _buildPanel() {
    return ExpansionPanelList(
      expansionCallback: (int index, bool isExpanded) {
        setState(() {
          for(int i = 0; i<_data.length; i++){
            _data[i].isExpanded = false;
          }
          
          _data[index].isExpanded = !isExpanded;
        });
      },
      children: _data.map<ExpansionPanel>((Item item) {
        return ExpansionPanel(
          canTapOnHeader: true,
          headerBuilder: (BuildContext context, bool isExpanded) {
            return ListTile(
              title: Text(item.headerValue),
            );
          },
          body: ListTile(
              title: Text(item.expandedValue),
              subtitle:
                  const Text('To delete this panel, tap the trash can icon'),
              trailing: const Icon(Icons.delete),
              onTap: () {
                setState(() {
                  _data.removeWhere((Item currentItem) => item == currentItem);
                });
              }),
          isExpanded: item.isExpanded,
        );
      }).toList(),
    );
  }
}