Getting started with the shutter AppBar

Achieve the effect diagram

Main code

class _MyHomePageState extends State<MyHomePage> {
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        leading: new Icon(Icons.arrow_back_ios),
        title: new Text(widget.title),
        backgroundColor: Colors.blue,
        centerTitle: true,
        actions: <Widget>[
          // Unhide menu 
          new IconButton(
            icon: new Icon(Icons.add_alarm),
            tooltip: 'Add Alarm',
            onPressed: () {},
          ),
          // The hidden menu 
          new PopupMenuButton<String>(
            itemBuilder: (BuildContext context) => <PopupMenuItem<String>>[
              this.getNewMenuItem(Icons.add_a_photo, ' menu 1', '1'),
              this.getNewMenuItem(Icons.add_location, ' menu 2', '2'),
              this.getNewMenuItem(Icons.audiotrack, ' menu 3', '3'),
            ],
            onSelected: (String action) {
              switch (action) {
                case '1':
                  {
                    print(' menu 1');
                  }
                  break;
                case '2':
                  {
                    print(' menu 2');
                  }
                  break;
                case '3':
                  {
                    print(' menu 3');
                  }
                  break;
                default:
              }
            },
          )
        ],
      ),
      body: Center(
        child: Column(
          mainAxisAlignment: MainAxisAlignment.center,
          children: <Widget>[
            Text(
              'Hi',
            ),
          ],
        ),
      ),
    );
  }

  getNewMenuItem(IconData icon, String text, String id) {
    return new PopupMenuItem<String>(
      value: id,
      child: new Row(
        mainAxisAlignment: MainAxisAlignment.spaceEvenly,
        children: <Widget>[
          new Icon(
            icon,
            color: Colors.blue,
          ),
          new Text(text)
        ],
      ),
    );
  }
}

Complete code

import 'package:flutter/material.dart';

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

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Flutter The title bar ',
      theme: ThemeData(
        primarySwatch: Colors.blue,
      ),
      home: MyHomePage(title: 'Flutter The title bar '),
    );
  }
}

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

  final String title;

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

class _MyHomePageState extends State<MyHomePage> {
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        leading: new Icon(Icons.arrow_back_ios),
        title: new Text(widget.title),
        backgroundColor: Colors.blue,
        centerTitle: true,
        actions: <Widget>[
          // Unhide menu 
          new IconButton(
            icon: new Icon(Icons.add_alarm),
            tooltip: 'Add Alarm',
            onPressed: () {},
          ),
          // The hidden menu 
          new PopupMenuButton<String>(
            itemBuilder: (BuildContext context) => <PopupMenuItem<String>>[
              this.getNewMenuItem(Icons.add_a_photo, ' menu 1', '1'),
              this.getNewMenuItem(Icons.add_location, ' menu 2', '2'),
              this.getNewMenuItem(Icons.audiotrack, ' menu 3', '3'),
            ],
            onSelected: (String action) {
              switch (action) {
                case '1':
                  {
                    print(' menu 1');
                  }
                  break;
                case '2':
                  {
                    print(' menu 2');
                  }
                  break;
                case '3':
                  {
                    print(' menu 3');
                  }
                  break;
                default:
              }
            },
          )
        ],
      ),
      body: Center(
        child: Column(
          mainAxisAlignment: MainAxisAlignment.center,
          children: <Widget>[
            Text(
              'Hi',
            ),
          ],
        ),
      ),
    );
  }

  getNewMenuItem(IconData icon, String text, String id) {
    return new PopupMenuItem<String>(
      value: id,
      child: new Row(
        mainAxisAlignment: MainAxisAlignment.spaceEvenly,
        children: <Widget>[
          new Icon(
            icon,
            color: Colors.blue,
          ),
          new Text(text)
        ],
      ),
    );
  }
}