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.

The results should look like this:

Build "Application.vala" just to make sure it all works. If something goes wrong here, feel free to refer back to 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:

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 (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 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 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:

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:

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:

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 .

Uninstalling the application

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

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

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.

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:

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.

Content Warnings

We use the 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 :

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.

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 .

Releases

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

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:

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:

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!

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:

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

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 .

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 will prompt you to remove your application.

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

If you'd like you can always read .

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:

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.

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:

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