Now that you've learned about Meson, the next step is to make your app able to be translated to different languages. The first thing you need to know is how to mark strings in your code as translatable. Here's an example:

stdout.printf ("Not Translatable string");
stdout.printf (_("Translatable string!"));

string normal = "Another non-translatable string";
string translated = _("Another translatable string");

See the difference? We marked the string as translatable by adding _() around it. Go back to your project and make all your strings translatable by adding _().

Now we have to make some changes to our Meson build system and add a couple new files to describe which files we want to translate and which languages we want to translate into.

1. Open up your "meson.build" file and add these lines below your project declaration:

   Copy

   # Include the translations module
   i18n = import('i18n')
   
   # Set our translation domain
   add_global_arguments('-DGETTEXT_PACKAGE="@0@"'.format (meson.project_name()), language:'c')

2. Remove the lines that install your .desktop and metainfo files and replace them with the following:

   Copy

   #Translate and install our .desktop file
   i18n.merge_file(
       input: 'data' / 'hello-again.desktop.in',
       output: meson.project_name() + '.desktop',
       po_dir: meson.project_source_root() / 'po',
       type: 'desktop',
       install: true,
       install_dir: get_option('datadir') / 'applications'
   )
   
   #Translate and install our .metainfo file
   i18n.merge_file(
       input: 'data' / 'hello-again.metainfo.xml.in',
       output: meson.project_name() + '.metainfo.xml',
       po_dir: meson.project_source_root() / 'po',
       install: true,
       install_dir: get_option('datadir') / 'metainfo'
   )

   The merge_file method combines translating and installing files, similarly to how the executable method combines building and installing your app. You might have noticed that this method has both an input argument and an output argument. We can use this instead of the rename argument from the install_data method.

3. Still in this file, add the following as the last line:

   Copy

   subdir('po')

4. You might have noticed in step 2 that the merge_file method has an input and output. We're going to append the additional extension .in to our .desktop and .metainfo.xml files so that this method can take the untranslated files and produce translated files with the correct names.

   Copy

   git mv data/hello-again.desktop data/hello-again.desktop.in
   git mv data/hello-again.metainfo.xml data/hello-again.metainfo.xml.in

   We use the git mv command here instead of renaming in the file manager or with mv so that git can keep track of the file rename as part of our revision history.

5. Now, Create a directory named "po" in the root folder of your project. Inside of your po directory you will need to create another "meson.build" file. This time, its contents will be:

   Copy

   i18n.gettext(meson.project_name(),
       args: '--directory=' + meson.project_source_root(),
       preset: 'glib'
   )

6. Inside of "po" create another file called "POTFILES" that will contain paths to all of the files you want to translate. For us, this looks like:

   Copy

   src/Application.vala
   data/hello-again.desktop.in
   data/hello-again.metainfo.xml.in

7. Now it's time to go back to your build directory and generate some new files using Terminal! The first one is our translation template or .pot file:

   Copy

   ninja io.github.yourusername.yourrepositoryname-pot

   After running this command you should notice a new file in the po directory containing all of the translatable strings for your app.

8. We have one more file to create in the "po" directory. This file will be named "LINGUAS" and it should contain the two-letter language codes for all languages you want to provide translations for. As an example, let's add German and Spanish

   Copy

   de
   es

9. Now we can use the template file to generate translation files for each of the languages we listed in the LINGUAS file with the following command:

   Copy

   ninja io.github.yourusername.yourrepositoryname-update-po

   You should notice two new files in your po directory called de.po and es.po. These files are now ready for translators to localize your app!

10. Last step. Don't forget to add all of the new files we created in the po directory to git:

    Copy

    git add src/Application.vala meson.build po/ data/
    git commit -am "Add translations"
    git push

That's it! Your app is now fully ready to be translated. Remember that each time you add new translatable strings or change old ones, you should regenerate your .pot and po files using the -pot and -update-po build targets from the previous two steps. If you want to support more languages, just list them in the LINGUAS file and generate the new po file with the -update-potarget. Don't forget to add any new po files to git!

Translators Comments

Sometimes detailed descriptions in the context of translatable strings are necessary for disambiguation or to help in the creation of accurate translations. For these situations use /// TRANSLATORS: comments.

/// TRANSLATORS: The first %s is search term, the second is the name of default browser
title = _("Search for %s in %s").printf (query, get_default_browser_name ());

The next thing we need is a build system. The build system that we're going to be using is called Meson. We already installed the meson program at the beginning of this book when we installed elementary-sdk. What we're going to do in this step is create the files that tell Meson how to install your program. This includes all the rules for building your source code as well as correctly installing your icons, .desktop, and metainfo files and the binary app that results from the build process.

Create a new file in your project's root folder called "meson.build". We've included some comments along the way to explain what each section does. You don't have to copy those, but type the rest into that file:

# project name, programming language, and required meson version
project('io.github.yourusername.yourrepositoryname',
    'vala', 'c',
    meson_version: '>= 0.56.0'
)

# Create a new executable, list the files we want to compile, list the dependencies we need, and install
executable(
    meson.project_name(),
    'src' / 'Application.vala',
    dependencies: [
        dependency('gtk4')
    ],
    install: true
)

# Install our .desktop file so the Applications Menu will see it
install_data(
    'data' / 'hello-again.desktop',
    install_dir: get_option('datadir') / 'applications',
    rename: meson.project_name() + '.desktop'
)

# Install our .metainfo.xml file so AppCenter will see it
install_data(
    'data' / 'hello-again.metainfo.xml',
    install_dir: get_option('datadir') / 'metainfo',
    rename: meson.project_name() + '.metainfo.xml'
)

Notice that in each of our install_data methods, we rename our files using our project name. By using our project name—and its RDNN scheme—we will ensure that our files are installed under a unique name that won't cause conflicts with other apps.

And you're done! Your app now has a real build system. This is a major milestone in your app's development!

Building and Installing with Meson

Now that we have a build system, let's try it out. Configure the build directory using the Meson command in Terminal:

meson setup build --prefix=/usr

This command tells Meson to get ready to build our app using the prefix "/usr" and that we want to build our app in a clean directory called "build". The meson setup command defaults to installing our app locally, but we want to install our app for all users on the computer.

Change into the build directory and use ninja to build. Then, if the build is successful, install with ninja install:

cd build
ninja
ninja install

If all went well, you should now be able to open your app from the Applications Menu and pin it to the Dock. We'll revisit Meson again later to add some more complicated behavior, but for now this is all you need to know to give your app a proper build system. If you want to explore Meson a little more on your own, you can always check out Meson's documentation.

Uninstalling the application

To uninstall your application, change into the build directory and we will use ninja once again to uninstall:

sudo ninja uninstall

If all went well, you should see command output that shows files related to your application were removed. Again, more details can be found in Meson's documentation.

Review

Let's review all we've learned to do:

• Create a new Gtk app using Gtk.Window, Gtk.Button, and Gtk.Label

• Keep our projects organized into branches

• License our app under the GPL and declare our app's authors in a standardized manner

• Create a .desktop file using RDNN that tells the computer how to display our app in the Applications Menu and the Dock

• Set up a Meson build system that contains all the rules for building our app and installing it cleanly

• Uninstall our application cleanly

That's a lot! You're well on your way to becoming a bona fide app developer for elementary OS. Give yourself a pat on the back, then take some time to play around with this example. Change the names of files and see if you can still build and install them properly. Ask another developer to clone your repo from GitHub and see if it builds and installs cleanly on their computer. If so, you've just distributed your first app! When you're ready, we'll move onto the next section: Translations.

In the previous chapter, we created a "Hello World!" app to show off our Vala and Gtk skills. But what if we wanted to share our new app with a friend? They'd have to know which packages to include with the valac command we used to build our app, and after they'd built it they'd have to run it from the build directory like we did. Clearly, we need to do some more stuff to make our app fit for people to use, to make it a real app.

Hello (Again) World!

To create our first real app, we're going to re-use what we learned in the last chapter and build on that example.

1. Create a new project folder, including a new "src" folder and an Application.vala file

2. Create a Gtk.Application class with a Gtk.ApplicationWindow in the activate () function.

3. Add a new Gtk.Label to the window with the text "Hello Again World!"

4. Finally, this time we're going to prefix our file with a small legal header. Make sure this header matches the license of your code and assigns copyright to you. More info about this later.

The results should look like this:

/*
 * SPDX-License-Identifier: GPL-3.0-or-later
 * SPDX-FileCopyrightText: 2023 Your Name <you@email.com>
 */
 
 public class MyApp : Gtk.Application {
    public MyApp () {
        Object (
            application_id: "io.github.yourusername.yourrepositoryname",
            flags: ApplicationFlags.FLAGS_NONE
        );
    }

    protected override void activate () {
        var label = new Gtk.Label ("Hello Again World!");
   
        var main_window = new Gtk.ApplicationWindow (this) {
            child = label,
            default_height = 300,
            default_width = 300,
            title = "Hello World"
        };
        main_window.present ();
    }

    public static int main (string[] args) {
        return new MyApp ().run (args);
    }
}

Build "Application.vala" just to make sure it all works. If something goes wrong here, feel free to refer back to the last chapter and remember to check your terminal output for any hints.

Initialize a git branch, add your files to the project, and write a commit message using what you learned in the last chapter. Lastly, make sure you've created a new repository for your project on GitHub push your first revision with git:

git remote add origin git@github.com:yourusername/yourrepositoryname.git
git push -u origin master

Everything working as expected? Good. Now, let's get our app ready for other people to use.

License

Since we're going to be putting our app out into the wild, we should include some information about who wrote it and the legal usage of its source code. For this we need a new file in our project's root folder: the LICENSE file. This file contains a copy of the license that your code is released under. For elementary OS apps this is typically the GNU General Public License (GPL). Remember the header we added to our source code? That header reminds people that your app is licensed and it belongs to you. GitHub has a built-in way to add several popular licenses to your repository. Read their documentation for adding software licenses and add a LICENSE file to your repository.

Next, we need a way to create a listing in AppCenter and a way to tell the interface to show our app in the Applications menu and dock: let's write some Metadata.

The last thing we need for a minimum-viable-app is to provide app icons. Apps on elementary OS provide icons hinted in 6 sizes: 16px, 24px, 32px, 48px, 64px, and 128px. These icons will be shown in many places throughout the system, such as those listed below:

Place your icons in the data directory and name them after their pixel sizes, such as32.svg, 64.svg, etc. The file structure should look like this:

hello-again
    data
        16.svg
        24.svg
        32.svg
        48.svg
        64.svg
        128.svg

Now that you have icon files in the data directory, add the following lines to the end of meson.build to install them .

# Install our icons in all the required sizes
icon_sizes = ['16', '24', '32', '48', '64', '128']

foreach i : icon_sizes
    install_data(
        'data' / i + '.svg',
        install_dir: get_option('datadir') / 'icons' / 'hicolor' / i + 'x' + i / 'apps',
        rename: meson.project_name() + '.svg'
    )
    install_data(
        'data' / i + '.svg',
        install_dir: get_option('datadir') / 'icons' / 'hicolor' / i + 'x' + i + '@2' / 'apps',
        rename: meson.project_name() + '.svg'
    )
endforeach

You'll notice the section for installing app icons is a little more complicated than installing other files. In this example, we're providing SVG icons in all of the required sizes for AppCenter and, since we're using SVG, we're installing them for both LoDPI and HiDPI. If you're providing PNG icons instead, you'll need to tweak this part a bit to handle assets exported for use on HiDPI displays.

If you cannot see your new icon in the Applications Menu or the Dock once you've reinstalled your app, refresh your system's icon cache using the following command:

sudo update-icon-caches /usr/share/icons/*

While having a build system is great, our app still isn't ready for regular users. We want to make sure our app can be built and installed without having to use Terminal. What we need to do is package our app. To do this, we use Flatpak on elementary OS. This section will teach you how to package your app as a Flatpak, which is required to publish apps in AppCenter. This will allow people to install your app and even get updates for it when you publish them.

Practice Makes Perfect

If you want to get really good really fast, you're going to want to practice. Repetition is the best way to commit something to memory. So let's recreate our entire Hello World app again from scratch:

1. Create a new branch folder "hello-packaging"

2. Set up our directory structure including the "src" and "data" folders.

3. Add your LICENSE, .desktop, .metainfo.xml, icons, and source code.

4. Now set up the Meson build system and translations.

5. Test everything!

Did you commit and push to GitHub for each step? Keep up these good habits and let's get to packaging this app!

Flatpak Manifest

The Flatpak manifest file describes your app's build dependencies and required permissions. Create a io.github.yourusername.yourrepositoryname.yml file in your project root with the following contents:

# This is the same ID that you've used in meson.build and other files
id: io.github.yourusername.yourrepositoryname

# Instead of manually specifying a long list of build and runtime dependencies,
# we can use a convenient pre-made runtime and SDK. For this example, we'll be
# using the runtime and SDK provided by elementary.
runtime: io.elementary.Platform
runtime-version: '8'
sdk: io.elementary.Sdk

# This should match the exec line in your .desktop file and usually is the same
# as your app ID
command: io.github.yourusername.yourrepositoryname

# Here we can specify the kinds of permissions our app needs to run. Since we're
# not using hardware like webcams, making sound, or reading external files, we
# only need permission to draw our app on screen using either X11 or Wayland.
finish-args:
  - '--share=ipc'
  - '--socket=fallback-x11'
  - '--socket=wayland'

# This section is where you list all the source code required to build your app.
# If we had external dependencies that weren't included in our SDK, we would list
# them here.
modules:
  - name: yourrepositoryname
    buildsystem: meson
    sources:
      - type: dir
        path: .

To run a test build and install your app, we can use flatpak-builder with a few arguments:

flatpak-builder build io.github.yourusername.yourrepositoryname.yml --user --install --force-clean

This tells Flatpak Builder to build the manifest we just wrote into a clean build folder the same as we did for Meson. Plus, we install the built Flatpak package locally for our user. If all goes well, congrats! You've just built and installed your app as a Flatpak.

That wasn't too bad, right? We'll set up more complicated packaging in the future, but this is all that is required to submit your app to AppCenter Dashboard for it to be built, packaged, and distributed. If you'd like you can always read more about Flatpak.

Uninstalling the application

Ninja and Flatpak both provide commands to uninstalling the application. It is recommended to use the provided method in both cases.

To remove our application with Flatpak, we will use Flatpak's remove command:

flatpak remove io.github.yourusername.yourrepositoryname

Flatpak will prompt you to remove your application.

flatpak uninstall io.github.yourusername.yourrepositoryname --delete-data


        ID                                                          Branch           Op
 1.     io.github.yourusername.yourrepositoryname                   master           r
 2.     io.github.yourusername.yourrepositoryname.Locale            master           r

Proceed with these changes to the user installation? [Y/n]:

Note: You can append -y to the command to bypass the dialog confirmation prompt

If you'd like you can always read more about Flatpak remove.

Continuous integration testing (also called CI), is a way to automatically ensure that your app builds correctly and has the minimum necessary configuration to run when it's installed. Setting up CI for your app can save you time and give you reassurance that when you submit your app for publishing it will pass the automated testing phase in AppCenter Dashboard. Keep in mind however, that there is also a human review portion of the submission process, so an app that passes CI may still need fixing before being published in AppCenter. Now that you have an app with a build system, metadata files, and packaging, we can configure CI using GitHub Actions.

1. Navigate to your project's page on GitHub and select the "Actions" tab.

2. Select "set up a workflow yourself". You'll then be shown the main.yml file with GitHub's default CI configuration. Replace the default workflow with the following:

name: CI

# This workflow will run for any pull request or pushed commit
on: [push, pull_request]

# A workflow run is made up of one or more jobs that can run sequentially or in parallel
jobs:
  # This workflow contains a single job called "flatpak"
  flatpak:
    # The type of runner that the job will run on
    runs-on: ubuntu-latest

    # This job runs in a special container designed for building Flatpaks for AppCenter
    container:
      image: ghcr.io/elementary/flatpak-platform/runtime:8
      options: --privileged

    # Steps represent a sequence of tasks that will be executed as part of the job
    steps:
      # Checks-out your repository under $GITHUB_WORKSPACE, so the job can access it
    - uses: actions/checkout@v3

      # Builds your flatpak manifest using the Flatpak Builder action
    - uses: flatpak/flatpak-github-actions/flatpak-builder@v6
      with:
        # This is the name of the Bundle file we're building and can be anything you like
        bundle: MyApp.flatpak
        # This uses your app's RDNN ID
        manifest-path: io.github.yourusername.yourrepositoryname.yml

        # You can automatically run any of the tests you've created as part of this workflow
        run-tests: true

        # These lines specify the location of the elementary Runtime and Sdk
        repository-name: appcenter
        repository-url: https://flatpak.elementary.io/repo.flatpakrepo
        cache-key: "flatpak-builder-${{ github.sha }}"

1. Select "Start commit" in the top right corner of the page to commit this workflow to your repository.

That's it! The Flatpak CI workflow will now run on your repository for any new commits or pull requests. You'll be able to see if the build succeeded or failed, and any reasons it might have failed. Configuring this CI workflow will help guide you during the development process and ensure that everything is working as intended.

This workflow will also produce a Flatpak Bundle file using GitHub Artifacts that you can download and install with Sideload. Using this bundle file, you can test feature or bug fix branches with your team, contributors, or community before merging the proposed fix into your main git branch.

GitHub Actions can be used to configure many more types of CI or other automation. For more information, check out the GitHub Actions website.

Every app comes with two metadata files that we can generate using an online tool. Open AppStream Metainfo Creator and fill out the form with your app's info:

Don't worry about generating Meson snippets, as we'll cover that in the next section. After you select "Generate", you should have two resulting files that you can copy.

MetaInfo

First is a MetaInfo file. This file contains all the information needed to list your app in AppCenter. It should look something like this:

<?xml version="1.0" encoding="UTF-8"?>
<component type="desktop-application">
  <id>io.github.myteam.myapp</id>

  <name>My App</name>
  <summary>Proves that we can use Vala and Gtk</summary>

  <metadata_license>CC-BY-4.0</metadata_license>
  <project_license>GPL-3.0-or-later</project_license>

  <description>
    <p>
      A quick summary of your app's main selling points and features. Just a couple sentences per paragraph is best
    </p>
  </description>

  <launchable type="desktop-id">io.github.myteam.myapp.desktop</launchable>
</component>

In your project's root, create a new folder called "data", and save your MetaInfo to a new file called "hello-again.metainfo.xml".

Screenshots

For the purposes of this tutorial, screenshots are optional, but they are required for publishing in AppCenter. Screenshots should only show your app on a transparent background and not contain any additional text or illustrations. You can use the caption tag to provide translatable and accessible descriptions of your screenshots.

<screenshots>
  <screenshot type="default">
    <caption>The most important feature of my app</caption>
    <image>https://raw.githubusercontent.com/myteam/myapp/1.0.0/data/screenshot.png</image>
  </screenshot>
</screenshots>

Content Warnings

We use the Open Age Rating Service (OARS) standard to describe sensitive content that may be present in your app so that people using it can be informed and actively consent to seeing that content. OARS data is required and can be generated by taking a short survey:

Branding

You can also specify a brand color for your app by adding the branding tag inside the component tag. Colors must be in hexadecimal, starting with #. The background will automatically be given a slight gradient in your app's banner.

<branding>
  <color type="primary">#f37329</color>
</branding>

Monetization

If you want to monetize your app, you will need to add two keys inside a custom tag inside the component tag. Suggested prices should be in whole USD. You also must include your app's AppCenter Stripe key. This is a unique public key for each app and is not the same as your Stripe account's regular public key. You can connect your app to Stripe and receive a new key on the AppCenter Dashboard.

<custom>
  <value key="x-appcenter-suggested-price">5</value>
  <value key="x-appcenter-stripe">pk_live_xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx</value>
</custom>

Releases

Your app must have a release tag for every version you wish to publish in AppCenter, including the initial release.

<releases>
  <release version="1.0.0" date="2022-09-08">
    <description>
      <p>Initial release, includes features such as:</p>
      <ul>
        <li>Application can be launched</li>
      </ul>
    </description>
  </release>
</releases>

Desktop Entry

This file contains all the information needed to display your app in the Applications Menu and in the Dock. The one generated from AppStream Metainfo Creator looks something like this:

[Desktop Entry]
Version=1.0
Type=Application

Name=My App
Comment=Proves that we can use Vala and Gtk
Categories=Development;Education;

Icon=io.github.myteam.myapp
Exec=io.github.myteam.myapp
Terminal=false

Copy the contents of your Desktop Entry and save it to the data folder you created earlier. Name this new file "hello-again.desktop".

Mark Your Progress

Each time we add a new file or make a significant change it's a good idea to commit a new revision and push to GitHub. Keep in mind that this acts as a backup system as well; when we push our work to GitHub, we know it's safe and we can always revert to a known good revision if we mess up later.

Add all of these files to git and commit a revision:

git add data/
git commit -am "Add Metadata files"
git push

Now that we've got all these swanky files laying around, we need a way to tell the computer what to do with them. Ready for the next chapter? Let's do this!