Bill Farmer

Random thoughts on random subjects

Android Flutter

by Bill Farmer. Categories: Hacking .

Google have made a big thing of their flutter development platform, so I thought I ought to give it a try. It’s easy to install, just download the sdk, unzip it in a suitable place and add the bin folder to your path.


I decided to have another look as it appears to be liked by developers on Reddit. The old version wouldn’t update, so I downloaded the latest (Flutter 3.16.5) and replaced it. This time it found everything it wanted. This time I build a simplistic app that just displays an image.

To remove the annoying diagonal banner on the debug version which overlays a possible icon on the app bar, add debugShowCheckedModeBanner: false to the MaterialApp widget. Because the image is larger than the display height in landscape, I added a SingleChildScrollView so that it can scroll. I also added a Padding widget so the image is inset slightly.

import 'package:flutter/material.dart';

void main() {
  runApp(const AnneApp());

class AnneApp extends StatelessWidget {
  const AnneApp({super.key});

  // This widget is the root of your application.
  Widget build(BuildContext context) {
    return MaterialApp(
      debugShowCheckedModeBanner: false,
      title: 'Anne',
      theme: ThemeData.dark(useMaterial3: true,),
      home: const Anne(title: 'Anne'),

class Anne extends StatelessWidget {
  const Anne({super.key, required this.title});

  final String title;

  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text(title),
      body: Center(
        child: SingleChildScrollView(
          child: Column(
            children: <Widget>[
                padding: const EdgeInsets.all(8.0),
                child: Image.asset('images/anne.png'),
              Text(title, style: Theme.of(context).textTheme.headlineLarge),

In order to include images, you need an assets entry in the pubspec.yaml file. The file includes helpful comments.

  # To add assets to your application, add an assets section, like this:
  # assets:
  #   - images/a_dot_burr.jpeg
  #   - images/a_dot_ham.jpeg
    - images/anne.png

The debug app is large (~70Mb) because it contains the flutter run time debugging system, also below. If you build a release version the app size is more reasonable.

$ flutter build apk
Running Gradle task 'assembleRelease'...                           14.4s
√  Built build\app\outputs\flutter-apk\app-release.apk (18.5MB).
Bill@Cecelia MINGW64 /d/flutter/Anne (main)
$ flutter install apk
Installing app-release.apk to Moto G...
Uninstalling old version...
Installing build\app\outputs\flutter-apk\app-release.apk...         8.1s

Building and installing the debug version of the app takes a long time. It is also slow starting, which is annoying. Because the release version is built with the debug keys by default, you can build and install that instead, which is much quicker.

$ flutter run
Launching lib\main.dart on Moto G in debug mode...
Running Gradle task 'assembleDebug'...                             22.2s
√  Built build\app\outputs\flutter-apk\app-debug.apk.
Installing build\app\outputs\flutter-apk\app-debug.apk...          22.7s
Syncing files to device Moto G...                                  198ms

I had to tell the earlier version (Flutter 2.2.3) where I had installed Android Studio.

$ flutter config --android-studio-dir 'D:\adt\Android Studio'
Setting "android-studio-dir" value to "D:\adt\Android Studio".

You may need to restart any open editors for them to read new settings.

$ flutter doctor -v
[] Flutter (Channel stable, 2.2.3, on Microsoft Windows [Version 10.0.19043.1110], locale en-GB)
    • Flutter version 2.2.3 at D:\adt\flutter
    • Framework revision f4abaa0735 (2 weeks ago), 2021-07-01 12:46:11 -0700
    • Engine revision 241c87ad80
    • Dart version 2.13.4

[] Android toolchain - develop for Android devices (Android SDK version 30.0.3)
    • Android SDK at D:\adt\android-sdk-windows
    • Platform android-30, build-tools 30.0.3
    • Java binary at: D:\adt\Android Studio\jre\bin\java
    • Java version OpenJDK Runtime Environment (build 11.0.8+10-b944.6842174)
    • All Android licenses accepted.

[] Chrome - develop for the web
    • Chrome at C:\Program Files (x86)\Google\Chrome\Application\chrome.exe

[] Android Studio
    • Android Studio at D:\adt\Android Studio
    • Flutter plugin can be installed from:
    • Dart plugin can be installed from:
    • android-studio-dir = D:\adt\Android Studio
    • Java version OpenJDK Runtime Environment (build 11.0.8+10-b944.6842174)

[] Connected device (2 available)
    • Moto G (mobile) • TA93003J7P • android-arm    • Android 7.1.2 (API 25)
    • Chrome (web)    • chrome     • web-javascript • Google Chrome 91.0.4472.124

• No issues found!

Having installed flutter and got it working, create a sample app.

$ flutter create --org org.billthefarmer --project-name hello --platforms android -t app hello
Creating project hello...
  hello\.gitignore (created)
  hello\.idea\libraries\Dart_SDK.xml (created)
  hello\.idea\libraries\KotlinJavaRuntime.xml (created)
  hello\.idea\modules.xml (created)
  hello\.idea\runConfigurations\main_dart.xml (created)
  hello\.idea\workspace.xml (created)
  hello\.metadata (created)
  hello\android\app\build.gradle (created)
  hello\android\app\src\main\kotlin\org\billthefarmer\hello\MainActivity.kt (created)
  hello\android\build.gradle (created)
  hello\android\hello_android.iml (created)
  hello\android\.gitignore (created)
  hello\android\app\src\debug\AndroidManifest.xml (created)
  hello\android\app\src\main\AndroidManifest.xml (created)
  hello\android\app\src\main\res\drawable\launch_background.xml (created)
  hello\android\app\src\main\res\drawable-v21\launch_background.xml (created)
  hello\android\app\src\main\res\mipmap-hdpi\ic_launcher.png (created)
  hello\android\app\src\main\res\mipmap-mdpi\ic_launcher.png (created)
  hello\android\app\src\main\res\mipmap-xhdpi\ic_launcher.png (created)
  hello\android\app\src\main\res\mipmap-xxhdpi\ic_launcher.png (created)
  hello\android\app\src\main\res\mipmap-xxxhdpi\ic_launcher.png (created)
  hello\android\app\src\main\res\values\styles.xml (created)
  hello\android\app\src\main\res\values-night\styles.xml (created)
  hello\android\app\src\profile\AndroidManifest.xml (created)
  hello\android\gradle\wrapper\ (created)
  hello\android\ (created)
  hello\android\settings.gradle (created)
  hello\lib\main.dart (created)
  hello\hello.iml (created)
  hello\pubspec.yaml (created)
  hello\ (created)
  hello\test\widget_test.dart (created)
Running "flutter pub get" in hello...                            1,323ms
Wrote 35 files.

All done!
In order to run your application, type:

  $ cd hello
  $ flutter run

Your application code is in hello\lib\main.dart.

And run it…

$ flutter run
Launching lib\main.dart on Moto G in debug mode...
Running Gradle task 'assembleDebug'...                             14.3s
√  Built build\app\outputs\flutter-apk\app-debug.apk.
Syncing files to device Moto G...                                  127ms

Flutter run key commands.
r Hot reload.
R Hot restart.
h Repeat this help message.
d Detach (terminate "flutter run" but leave application running).
c Clear the screen
q Quit (terminate the application on the device).

 Running with sound null safety

An Observatory debugger and profiler on Moto G is available at:
The Flutter DevTools debugger and profiler on Moto G is available at:

Application finished.

Screenshot of resulting app.

Flutter app

Flutter created a minimal kotlin file, MainActivity.kt.

package org.billthefarmer.hello


class MainActivity: FlutterActivity() {

And a dart file, main.dart.

import 'package:flutter/material.dart';

void main() {

class MyApp extends StatelessWidget {
  // This widget is the root of your application.
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Flutter Demo',
      theme: ThemeData(
        // This is the theme of your application.
        // Try running your application with "flutter run". You'll see the
        // application has a blue toolbar. Then, without quitting the app, try
        // changing the primarySwatch below to and then invoke
        // "hot reload" (press "r" in the console where you ran "flutter run",
        // or simply save your changes to "hot reload" in a Flutter IDE).
        // Notice that the counter didn't reset back to zero; the application
        // is not restarted.
      home: MyHomePage(title: 'Flutter Demo Home Page'),

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

  // This widget is the home page of your application. It is stateful, meaning
  // that it has a State object (defined below) that contains fields that affect
  // how it looks.

  // This class is the configuration for the state. It holds the values (in this
  // case the title) provided by the parent (in this case the App widget) and
  // used by the build method of the State. Fields in a Widget subclass are
  // always marked "final".

  final String title;

  _MyHomePageState createState() => _MyHomePageState();

class _MyHomePageState extends State<MyHomePage> {
  int _counter = 0;

  void _incrementCounter() {
    setState(() {
      // This call to setState tells the Flutter framework that something has
      // changed in this State, which causes it to rerun the build method below
      // so that the display can reflect the updated values. If we changed
      // _counter without calling setState(), then the build method would not be
      // called again, and so nothing would appear to happen.

  Widget build(BuildContext context) {
    // This method is rerun every time setState is called, for instance as done
    // by the _incrementCounter method above.
    // The Flutter framework has been optimized to make rerunning build methods
    // fast, so that you can just rebuild anything that needs updating rather
    // than having to individually change instances of widgets.
    return Scaffold(
      appBar: AppBar(
        // Here we take the value from the MyHomePage object that was created by
        // the method, and use it to set our appbar title.
        title: Text(widget.title),
      body: Center(
        // Center is a layout widget. It takes a single child and positions it
        // in the middle of the parent.
        child: Column(
          // Column is also a layout widget. It takes a list of children and
          // arranges them vertically. By default, it sizes itself to fit its
          // children horizontally, and tries to be as tall as its parent.
          // Invoke "debug painting" (press "p" in the console, choose the
          // "Toggle Debug Paint" action from the Flutter Inspector in Android
          // Studio, or the "Toggle Debug Paint" command in Visual Studio Code)
          // to see the wireframe for each widget.
          // Column has various properties to control how it sizes itself and
          // how it positions its children. Here we use mainAxisAlignment to
          // center the children vertically; the main axis here is the vertical
          // axis because Columns are vertical (the cross axis would be
          // horizontal).
          children: <Widget>[
              'You have pushed the button this many times:',
              style: Theme.of(context).textTheme.headline4,
      floatingActionButton: FloatingActionButton(
        onPressed: _incrementCounter,
        tooltip: 'Increment',
        child: Icon(Icons.add),
      ), // This trailing comma makes auto-formatting nicer for build methods.

The generated application file is approximately 50Mb in size, nearly all of which is flutter run time libraries, kotlin, androidx, etc. Rather a lot of bloat, considering that most of my apps are about 200Kb in size.

See Also