How To Create Popup Menu Items In Flutter Android App

dependencies:
  flutter:
    sdk: flutter
  popup_menu: ^1.0.5

flutter pub get

import 'package:popup_menu/popup_menu.dart';

import 'package:flutter/material.dart';
import 'package:popup_menu/popup_menu.dart';

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

class MyApp extends StatelessWidget {
  // This widget is the root of your application.
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      debugShowCheckedModeBanner: false,
      title: 'Flutter Demo',
      home: MyHomePage(title: 'Popup Menu'),
    );
  }
}

class MyHomePage extends StatefulWidget {
  MyHomePage({Key key, this.title}) : super(key: key);

  final String title;

  @override
  _MyHomePageState createState() => _MyHomePageState();
}

class _MyHomePageState extends State<MyHomePage> {
  PopupMenu menu;
  GlobalKey btnKey = GlobalKey();
  GlobalKey btnKey2 = GlobalKey();
  GlobalKey btnKey3 = GlobalKey();

  @override
  void initState() {
    super.initState();

    menu = PopupMenu(items: [
      MenuItem(
          title: 'Mail',
          image: Icon(
            Icons.mail,
            color: Colors.white,
          )),
      MenuItem(
          title: 'Power',
          image: Icon(
            Icons.power,
            color: Colors.white,
          )),
      MenuItem(
          title: 'Setting',
          image: Icon(
            Icons.settings,
            color: Colors.white,
          )),
      MenuItem(
          title: 'PopupMenu',
          image: Icon(
            Icons.menu,
            color: Colors.white,
          ))
    ], 
onClickMenu: onClickMenu, onDismiss: onDismiss, maxColumn: 4);
  }

  void stateChanged(bool isShow) {
    print('menu is ${isShow ? 'showing' : 'closed'}');
  }

  void onClickMenu(MenuItemProvider item) {
    print('Click menu -> ${item.menuTitle}');
  }

  void onDismiss() {
    print('Menu is dismiss');
  }

  @override
  Widget build(BuildContext context) {
    PopupMenu.context = context;

    return Scaffold(
      appBar: AppBar(
        backgroundColor: Colors.lightGreen,
        title: Text(widget.title),
      ),
      body: Container(
        alignment: Alignment.center,
        child: Column(
          mainAxisAlignment: MainAxisAlignment.center,
          children: <Widget>[
            Container(
              color: Colors.lightGreen,
              child: MaterialButton(
                height: 45.0,
                key: btnKey,
                onPressed: maxColumn,
                child: Text('Show Menu'),
              ),
            ),
           SizedBox(width: 0, height: 24),
            Container(
              color: Colors.pink,
              child: MaterialButton(
                key: btnKey2,
                height: 45.0,
                onPressed: customBackground,
                child: Text('Show Menu'),
              ),
            ),
           SizedBox(width: 0, height: 24),
            Container(
              color: Colors.lightGreen,
              child: MaterialButton(
                key: btnKey3,
                height: 45.0,
                onPressed: onDismissOnlyBeCalledOnce,
                child: Text('Show Menu'),
              ),
            ),
          ],
        ),
      ),
    );
  }

  void onDismissOnlyBeCalledOnce() {
    menu.show(widgetKey: btnKey3);
  }


  void checkState(BuildContext context) {
    final snackBar = new SnackBar(content: new Text('SnackBar!'));

    Scaffold.of(context).showSnackBar(snackBar);
  }

  void maxColumn() {
    PopupMenu menu = PopupMenu(
        maxColumn: 3,
        items: [
          MenuItem(
              title: 'Power',
              image: Icon(
                Icons.power,
                color: Colors.white,
              )),
          MenuItem(
              title: 'Setting',
              image: Icon(
                Icons.settings,
                color: Colors.white,
              )),
          MenuItem(
              title: 'PopupMenu',
              image: Icon(
                Icons.menu,
                color: Colors.white,
              ))
        ],
        onClickMenu: onClickMenu,
        stateChanged: stateChanged,
        onDismiss: onDismiss);
    menu.show(widgetKey: btnKey);
  }

  //
  void customBackground() {
    PopupMenu menu = PopupMenu(
        items: [
          MenuItem(
              title: 'Home',
              image: Icon(
                Icons.home,
                color: Colors.white,
              )),
          MenuItem(
              title: 'Mail',
              image: Icon(
                Icons.mail,
                color: Colors.white,
              )),
          MenuItem(
              title: 'Power',
              image: Icon(
                Icons.power,
                color: Colors.white,
              )),
          MenuItem(
              title: 'Setting',
              image: Icon(
                Icons.settings,
                color: Colors.white,
              )),
          MenuItem(
              title: 'PopupMenu',
              image: Icon(
                Icons.menu,
                color: Colors.white,
              ))
        ],
        onClickMenu: onClickMenu,
        stateChanged: stateChanged,
        onDismiss: onDismiss);
    menu.show(widgetKey: btnKey2);
  }
}