It is very common to have App Bar in mobile apps, most mobile apps have app bar. We also known as action bar in mobile apps. App Bar or top App Bars is a collection of widget located at the top of the app, for wrapping our app’s title, icon and action link. This app bar will work the same looks, style both in Android and IOS. Basically almost everything will work the same, Flutter is cross platform mobile app Framework.

Here’s example code of App Bar in Flutter with icon, title and action:

import 'package:flutter/material.dart';

void main() {
  runApp(new MyApp());
}
class MyApp extends StatelessWidget {

  @override
  Widget build(BuildContext context) {
    return new MaterialApp(
      title: 'Home',
      theme: new ThemeData(
        primarySwatch: Colors.blue,
        primaryColor: const Color(0xFF2196f3),
        accentColor: const Color(0xFF2196f3),
        canvasColor: const Color(0xFFfafafa),
      ),
      home: new MyHomePage(),
    );
  }
}

class MyHomePage extends StatefulWidget {
  MyHomePage({Key key}) : super(key: key);
  @override
  MyHomePageState createState() => new MyHomePageState();
}

class _MyHomePageState extends State {
    @override
    Widget build(BuildContext context) {
      return new Scaffold(
        appBar: AppBar(
          title: new Text('Home'),
          actions: [
            // action button
            IconButton(
              icon: Icon( Icons.search ),
              onPressed: () { },
            ),
          ],
          leading: IconButton(
            icon: Image.asset('Your Image/Logo'), 
            onPressed: () { },
          ),
         ),
      );
    }
}

Here’s example code of App Bar in Flutter with icon, title and action with popup menu:

import 'package:flutter/material.dart';

void main() {
  runApp(new MyApp());
}
class MyApp extends StatelessWidget {

  @override
  Widget build(BuildContext context) {
    return new MaterialApp(
      title: 'Home',
      theme: new ThemeData(
        primarySwatch: Colors.blue,
        primaryColor: const Color(0xFF2196f3),
        accentColor: const Color(0xFF2196f3),
        canvasColor: const Color(0xFFfafafa),
      ),
      home: new MyHomePage(),
    );
  }
}

class MyHomePage extends StatefulWidget {
  MyHomePage({Key key}) : super(key: key);
  @override
  MyHomePageState createState() => new MyHomePageState();
}

class _MyHomePageState extends State {
    @override
    Widget build(BuildContext context) {
      return new Scaffold(
        appBar: AppBar(
          title: new Text('Guest'),
          actions: [
            myPopMenu();
          ],
          leading: IconButton(
            icon: Image.asset('Your Image/Logo'), 
            onPressed: () { },
          ),
         ),
      );
    }

Widget myPopMenu() {
    return PopupMenuButton(
        onSelected: (value) {
          if(value==1){
           //action for Add Appointment
          }else if(value==2){
           //action for Add Medicine
          }else if(value==3){
           //action for Logout
          }
        },
        itemBuilder: (context) => [
          PopupMenuItem(
              value: 1,
              child: Row(
                children: <Widget>[
                  Text('Add Appointment')
                ],
              )),
          PopupMenuItem(
              value: 2,
              child: Row(
                children: <Widget>[
                  Text('Add Medicine')
                ],
              )),
          PopupMenuItem(
              value: 3,
              child: Row(
                children: <Widget>[
                  Text('Logout')
                ],
              )),
        ]);
  }
}