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
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).
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/ - 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