Flutter Application¶

Flutter is Google’s UI toolkit for building natively compiled applications for mobile, web, and desktop from a single codebase. In page you will learn how to pack a Flutter desktop project for Linux using the AppImage format.

For the purpose we will be using a simple hello world application which is available at: https://github.com/AppImageCrafters/appimage-builder-flutter-example

Preparing your system¶

Building the flutter app¶

We will use the linux desktop target of Flutter to generate our application binaries. This target is currently only available in the beta channel therefore we need to enable it. Once it’s enable we can generate the binaries.

# enable desktop builds
flutter channel beta
flutter upgrade
flutter config --enable-linux-desktop

# build desktop release
flutter build linux

Our application binaries should be somewhere inside the build dir, usually build/linux/x64/release/bundle. We will copy this this folder to our work dir as AppDir:

cp build/linux/x64/release/bundle $PWD/AppDir

Generating the recipe¶

We will use the –generate method to draft an initial recipe for our project. In the process you’ll be prompted with a set of questions that will help the tool to process your project.

Notice that the application must run in order to properly analyse it’s runtime dependencies.

appimage-builder --generate

Basic Information :
? ID [Eg: com.example.app] : com.example.flutter_hello
? Application Name : Flutter Hello
? Icon : utilities-terminal
? Version : latest
? Executable path relative to AppDir [usr/bin/app] : hello_flutter
? Arguments [Default: $@] : $@
? Update Information [Default: guess] : guess
? Architecture :  amd64

Generating the AppImage¶

At this point we should have a working recipe that can be used to generate an AppImage from our flutter project. To do so execute appimage-builder and the packaging process will start.

After deploying the runtime dependencies to the AppDir and configuring then the tool will proceed to test the application according to test cases defined in the recipe. This will give us the certainty that our app runs in the target system. It’s up to you to manually verify that all features work as expected. Once the tools completes its execution you should find an AppImage file in your current work dir.

appimage-builder --recipe AppImageBuilder.yml

Polishing the recipe¶

Hooray! You should have now an AppImage that can be shipped to any GLibC based GNU/Linux distribution. But there is some extra work to do. The recipe we have is made to freeze the current runtime which include certain parts of your system (such as theme modules) that may not be required in the final bundle. Therefore we will proceed to remove them from the recipe.

Grab your favourite text editor and open the AppImageBuilder.yml file.

Deploy binaries from the script section¶

Every time we run appimage-builder we need to first copy the application binaries into the AppDir. This step can be made part of the recipe as using the script section as follows:

script:
 - rm -rf AppDir | true
 - cp -r build/linux/x64/release/bundle $APPDIR

Notice the usage of the APPDIR environment variable, this is exported by appimage-builder at runtime.

Refine the packages include list¶

In the apt > include section you may find a list of packages. Those packages that are tightly related to your desktop environment (in my case KDE) or to some external system service can be removed in order to save some space but you will have to always validate the resulting bundle using the tests cases. You can even try to boil down your list to only libgtk-3-0 and manually add the missing libs (if any).

Final recipe¶

After following the tutorial you should end with a recipe similar to this one. It could be used as starting point if you don’t want to use the –generate method.

# appimage-builder recipe see https://appimage-builder.readthedocs.io for details
version: 1
script:
 - rm -rf AppDir || true
 - cp -r build/linux/x64/release/bundle AppDir
 - mkdir -p AppDir/usr/share/icons/hicolor/64x64/apps/
 - mv AppDir/lib/ AppDir/usr/
 - cp flutter-mark-square-64.png AppDir/usr/share/icons/hicolor/64x64/apps/
AppDir:
  path: ./AppDir
  app_info:
    id: org.appimagecrafters.hello-flutter
    name: Hello Flutter
    icon: flutter-mark-square-64
    version: latest
    exec: hello_flutter
    exec_args: $@
  apt:
    arch: amd64
    allow_unauthenticated: true
    sources:
    - sourceline: deb http://archive.ubuntu.com/ubuntu/ bionic main restricted universe multiverse
    - sourceline: deb http://archive.ubuntu.com/ubuntu/ bionic-updates main restricted universe multiverse
    - sourceline: deb http://archive.ubuntu.com/ubuntu/ bionic-backports main restricted universe multiverse
    - sourceline: deb http://security.ubuntu.com/ubuntu bionic-security main restricted universe multiverse
    include:
    - libgtk-3-0
    exclude:
    - humanity-icon-theme
    - hicolor-icon-theme
    - adwaita-icon-theme
    - ubuntu-mono
  files:
    exclude:
    - usr/share/man
    - usr/share/doc/*/README.*
    - usr/share/doc/*/changelog.*
    - usr/share/doc/*/NEWS.*
    - usr/share/doc/*/TODO.*
  test:
    fedora:
      image: appimagecrafters/tests-env:fedora-30
      command: ./AppRun
      use_host_x: true
    debian:
      image: appimagecrafters/tests-env:debian-stable
      command: ./AppRun
      use_host_x: true
    arch:
      image: appimagecrafters/tests-env:archlinux-latest
      command: ./AppRun
      use_host_x: true
    centos:
      image: appimagecrafters/tests-env:centos-7
      command: ./AppRun
      use_host_x: true
    ubuntu:
      image: appimagecrafters/tests-env:ubuntu-xenial
      command: ./AppRun
      use_host_x: true
AppImage:
  arch: x86_64
  update-information: guess
  sign-key: None