How To Toggle Popup Menu Button Using Flutter Android App

import 'package:flutter/material.dart';

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

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      debugShowCheckedModeBanner: false,
      home: MyHomePage(),
    );
  }
}

class MyHomePage extends StatefulWidget {
  @override
  _MyHomePageState createState() => _MyHomePageState();
}

class _MyHomePageState extends State<MyHomePage> {
  bool isSignedIn = false;
  _onSelected(dynamic val) {
    setState(() => isSignedIn = !isSignedIn);
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
        appBar: AppBar(
          backgroundColor: Colors.blue[900],
          title: Text("Toggle Popup Menu Button"),
          actions: <Widget>[
            PopupMenuButton(
              onSelected: _onSelected,
              icon: Icon(Icons.menu),
              itemBuilder: (context) => [
                PopupMenuItem(
                  child: Text(isSignedIn ? "LogOut" : "Sign In"),
                ),
              ],
            ),
          ],
        ),
        body: Center(
          child: Text("Main Body"),
        ));
  }
}