import 'package:flutter/material.dart';

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

class MenuApp extends StatelessWidget {
  const MenuApp({super.key});

  @override
  Widget build(BuildContext context) {
    return const MaterialApp(
      home: Scaffold(body: MyCascadingMenu()),
    );
  }
}

class MyCascadingMenu extends StatefulWidget {
  const MyCascadingMenu({super.key});

  @override
  State<MyCascadingMenu> createState() => _MyCascadingMenuState();
}

class _MyCascadingMenuState extends State<MyCascadingMenu> {
  final FocusNode _buttonFocusNode = FocusNode();

  @override
  Widget build(BuildContext context) {
    return Column(
      crossAxisAlignment: CrossAxisAlignment.start,
      children: <Widget>[
        MenuAnchor(
          childFocusNode: _buttonFocusNode,
          menuChildren: <Widget>[
            MenuItemButton(onPressed: () {}, child: const Text('1')),
            MenuItemButton(onPressed: () {}, child: const Text('2')),
            SubmenuButton(
              menuChildren: <Widget>[
                MenuItemButton(onPressed: () {}, child: const Text('3-1')),
                SubmenuButton(
                  menuChildren: <Widget>[
                    MenuItemButton(
                        onPressed: () {}, child: const Text('3-2-1')),
                    MenuItemButton(
                        onPressed: () {}, child: const Text('3-2-2')),
                  ],
                  child: const Text('3-2'),
                ),
                MenuItemButton(onPressed: () {}, child: const Text('3-3')),
              ],
              child: const Text('3'),
            ),
            SubmenuButton(
              menuChildren: <Widget>[
                MenuItemButton(onPressed: () {}, child: const Text('4-1')),
                MenuItemButton(onPressed: () {}, child: const Text('4-2')),
              ],
              child: const Text('4'),
            ),
            MenuItemButton(onPressed: () {}, child: const Text('5')),
            MenuItemButton(onPressed: () {}, child: const Text('6')),
          ],
          builder: (
            BuildContext context,
            MenuController controller,
            Widget? child,
          ) {
            return TextButton(
              focusNode: _buttonFocusNode,
              onPressed: () {
                if (controller.isOpen) {
                  controller.close();
                } else {
                  controller.open();
                }
              },
              child: const Text('OPEN MENU'),
            );
          },
        ),
      ],
    );
  }
}