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How to port a Sugar application with Sugarapp and package it with Flatpak (by example)

As a first step read this blog post to understand the context and scope of this project.


You already know the basics for:

  1. Use the Linux terminal.
  2. Python programming.
  3. Git.

Setting up the development environment

  1. Install Flatpak and add the Flathub repository. Find the instructions for almost every Linux distribution here.

  2. Double check that everything is setup correctly by installing and running an existing application from the terminal.

    $ flatpak install flathub org.sugarlabs.BaseApp
  3. Use this BaseApp as a development environment, it already comes with all the basic dependencies we need. Including Sugarapp, which is the main library we use to port the Sugar applications to the desktop.

    $ flatpak run --command=bash org.sugarlabs.BaseApp # Enter the development environment
    $ exit # Exit the development environment

Porting an application with Sugarapp

  1. Get the application source code. Let's use HelloWorld application as an example.

    $ git clone
    $ cd hello-world
  2. Identify the main activity class.

    $ cat activity/ | grep exec # To find the main class
    $ vim # Edit the file with you preferred text editor
  3. Replace the Sugar Activity class by the Sugarapp SugarCompatibleActivity class.

    diff --git a/ b/
    index f6f1634..e4e6607 100644
    --- a/
    +++ b/
    @@ -30,13 +30,15 @@ from sugar3.activity.widgets import StopButton
     from sugar3.activity.widgets import ShareButton
     from sugar3.activity.widgets import DescriptionItem
    +from sugarapp.widgets import SugarCompatibleActivity
    -class HelloWorldActivity(activity.Activity):
    +class HelloWorldActivity(SugarCompatibleActivity):
         """HelloWorldActivity class as specified in"""
         def __init__(self, handle):
             """Set up the HelloWorld activity."""
    -        activity.Activity.__init__(self, handle)
    +        SugarCompatibleActivity.__init__(self, handle)
             # we do not have collaboration features
             # make the share option insensitive
  4. Run the application with Sugarapp.

    $ cat activity/ | grep bundle_id # In this example, the app-id is org.sugarlabs.HelloWorld
    $ flatpak run --command=bash --filesystem=$PWD --socket=session-bus --socket=x11 org.sugarlabs.BaseApp # To enter the development environment
    $ SUGAR_BUNDLE_ID=org.sugarlabs.HelloWorld SUGAR_BUNDLE_PATH=$PWD sugarapp
  5. Extend toolbars to be able to save and load projects.

    Sugar applications can automatically save and load projects, e.g. a user starts a new project in MusicKeyboard and then simply closes the application. The project will be restored when the user re-opens the application. This is supported by the Sugar API, where every application can provide a write_file and read_file method.

    Sugarapp mimics this behavior by always providing a valid file_path to these methods. Sugarapp can also to extend the application UI by providing widgets to support saving and loading files, just like any other desktop application. As an example:

    diff --git a/ b/
    index b8d179a..76ad943 100644
    --- a/
    +++ b/
    @@ -25,9 +25,9 @@ from gettext import gettext as _
     from sugar3.activity import activity
     from import ToolbarBox
     from sugar3.activity.widgets import StopButton
    -from sugar3.activity.widgets import ActivityToolbarButton
     from sugarapp.widgets import SugarCompatibleActivity
    +from sugarapp.widgets import ExtendedActivityToolbarButton
     class HelloWorldActivity(SugarCompatibleActivity):
    @@ -44,7 +44,7 @@ class HelloWorldActivity(SugarCompatibleActivity):
             # toolbar with the new toolbar redesign
             toolbar_box = ToolbarBox()
    -        activity_button = ActivityToolbarButton(self)
    +        activity_button = ExtendedActivityToolbarButton(self)
             toolbar_box.toolbar.insert(activity_button, 0)

    To see the most common issues take a look at this list.

  6. Before we can move on to packaging, we need to make sure the activity/ file has all the required fields.

    diff --git a/activity/ b/activity/
    index 4c1a510..6da1a7a 100644
    --- a/activity/
    +++ b/activity/
    @@ -2,7 +2,16 @@
     name = HelloWorld
     activity_version = 7
     bundle_id = org.sugarlabs.HelloWorld
    +release_date = 2020-03-12
     exec = sugar-activity3 activity.HelloWorldActivity
     icon = activity-helloworld
     license = GPLv2+
    +metadata_license = CC0-1.0
     repository =
    +summary = A demo Sugar application
    +description = HelloWorld is a demo application used in tutorials for developing new Sugar applications or porting Sugar applications to Flatpak.
    +url =
    +tags = Education
    +update_contact =
    +developer_name = Sugar Labs Community
    +screenshots =

    Most of the missing information can be found in places like ASLO, help pages and the git repository it-self. Note that it is recommended to rename the bundle_id to something that starts with org.sugarlabs. so we can publish Sugar applications with a consistent and more useful identity.

  7. We need to create patches for the changes we made. As an example, one patch for the changes to the file. It can be called helloworld-info.patch. It's preferred to separate patches for bug fixes and other issues. This will simplify the process of up-streaming bug fixes later.

    $ git diff activity/ > helloworld-info.patch
    $ git diff > helloworld-port.patch

Packaging the applications with Flatpak

  1. The application is ready for the desktop. Now we need to write a Flatpak manifest to build and package the application. A manifest is a JSON file with all the information needed to build the application.

        "app-id": "org.sugarlabs.HelloWorld",
        "base": "org.sugarlabs.BaseApp",
        "base-version": "22.06",
        "runtime": "org.gnome.Platform",
        "runtime-version": "42",
        "sdk": "org.gnome.Sdk",
        "separate-locales": false,
        "command": "sugarapp",
        "finish-args": [
        "modules": [
                "name": "hello-world",
                "buildsystem": "simple",
                "build-commands": [
                    "python3 install --prefix=${FLATPAK_DEST} --skip-install-desktop-file --skip-install-mime"
                "sources": [
                        "type": "git",
                        "url": "",
                        "branch": "master",
                        "commit": "244bcaf802b5a093787a121ddcbefc0bec917a8e"
                        "type": "patch",
                        "path": "helloworld-port.patch"
                        "type": "patch",
                        "path": "helloworld-info.patch"
                "post-install": [
                    "sugarapp-gen-mimetypes activity/ mimetypes",
                    "sugarapp-gen-appdata activity/ appdata",
                    "sugarapp-gen-desktop activity/ desktop --mimetypes mimetypes",
                    "install -D mimetypes /app/share/mime/packages/org.sugarlabs.HelloWorld.xml",
                    "install -D mimetypes /app/share/sugar/activities/HelloWorld.activity/activity/mimetypes.xml",
                    "install -D appdata /app/share/metainfo/org.sugarlabs.HelloWorld.appdata.xml",
                    "install -D desktop /app/share/applications/org.sugarlabs.HelloWorld.desktop",
                    "install -D activity/activity-helloworld.svg /app/share/icons/hicolor/scalable/apps/org.sugarlabs.HelloWorld.svg"

    To learn more about the manifest just take a look at the Flatpak documentation.

  2. Let's build and run the application now.

    $ flatpak-builder --user --force-clean --install build org.sugarlabs.HelloWorld.json
    $ flatpak run org.sugarlabs.HelloWorld//master
  3. Once it's installed, we need to double check that the metadata was generated correctly.

    $ flatpak install flathub org.freedesktop.appstream-glib # Install the tools
    $ desktop-file-validate /var/lib/flatpak/app/org.sugarlabs.HelloWorld/current/active/files/share/applications/org.sugarlabs.HelloWorld.desktop
    $ appstream-util validate /var/lib/flatpak/app/org.sugarlabs.HelloWorld/current/active/files/share/appdata/org.sugarlabs.HelloWorld.appdata.xml

    If both commands finish without errors, it means we are ready!

  4. Create a new repository in Github, as an example,<YOUR_USER>/org.sugarlabs.HelloWorld, and then commit and push changes there.

    $ git clone<YOUR_USER>/org.sugarlabs.HelloWorld.git
    $ cd org.sugarlabs.HelloWorld
    $ git add org.sugarlabs.HelloWorld.json # and all the other files referrenced in your manifest
    $ git commit -m "Add org.sugarlabs.HelloWorld"
    $ git push origin master

And that's it for now! You can find the full example here.