How To Set Up Dropdown Menu In Appbar In Flutter App

import 'package:flutter/material.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(),
    );
  }
}

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: Icon(
          Icons.menu,
        ),
        centerTitle: true,
        title: Text('App Design',style: TextStyle(
          fontSize: 18.0,
          fontWeight: FontWeight.bold,
        ),
        ),
        backgroundColor: Colors.black,
        actions: <Widget>[
          PopupMenuButton(
            itemBuilder: (BuildContext context) {
              return [
                PopupMenuItem(
                    child: InkWell(
                        splashColor: Colors.grey, // splash color
                        child: Text('Home')
                    )
                ),
                PopupMenuItem(
                    child: InkWell(
                        splashColor: Colors.grey, // splash color
                        child: Text('Bookmarks')
                    )
                ),
                PopupMenuItem(
                    child: InkWell(
                        splashColor: Colors.grey, // splash color
                        child: Text('Seeting')
                    )
                ),
              ];
            },
          )
        ],
      ),
    );
  }
}