Hello World!

Now that we have a working installation of Kotlin/Native, let’s start building our first gtk-kn app.

Firstly, we need to create a GTK Application instance with an application ID. To do this, we must add the gtk-kn library dependencies to our build.gradle.kts file. Open the file and replace the comment // Dependencies goes here with the gtk-kn dependency implementation("org.gtkkn:gtk4:0.0.1-SNAPSHOT").

Next, we need to edit the hello.kt file and replace its contents with the following:

// hello.kt
import org.gtkkn.bindings.gio.ApplicationFlags
import org.gtkkn.bindings.gtk.Application

private const val APP_ID = "org.gtkkn.samples.gtk.playground"

fun main() {
    Application(APP_ID, ApplicationFlags.FLAGS_NONE)
        .run(0, emptyList())
}

From the root project directory, run the build command:

./gradlew runDebugExecutableLinuxX64

It builds fine, but nothing but a warning in our terminal appears:

Warning

GLib-GIO-WARNING **: 20:36:01.273: Your application does not implement g_application_activate() and has no handlers connected to the ‘activate’ signal. It should do one of these.

GTK tells us that something should be called in its activate step. So let’s create a GTK ApplicationWindow there:

// hello.kt
import org.gtkkn.bindings.gio.ApplicationFlags
import org.gtkkn.bindings.gtk.Application
import org.gtkkn.bindings.gtk.ApplicationWindow

private const val APP_ID = "org.gtkkn.samples.gtk.playground"

fun main() {
    // Create a new application
    val app = Application(APP_ID, ApplicationFlags.FLAGS_NONE)

    // Connect to "activate" signal of `app`
    app.connectActivate {

        // Create a window and set the title
        val window = ApplicationWindow(app)
        window.setTitle("My GTK App")

        // Present window
        window.present()
    }

    // Run the application
    app.run(0, emptyList())
}

That is better!

That’s much better! Now we have a working window. But, of course, we want to do more than just display an empty window. Let’s add a button to our app:

samples/gtk/hello-world/src/nativeMain/kotlin/hello.kt

private const val APP_ID = "org.gtkkn.samples.gtk.helloworld"

fun main() {
    // Create a new application
    val app = Application(APP_ID, ApplicationFlags.FLAGS_NONE)

    // Connect to "activate" signal of `app`
    app.connectActivate {
        // Create a button with label and margins
        val button = Button()
        button.setLabel("Click me!")
        button.setMargins(12)

        // Connect to "clicked" signal of `button`
        button.connectClicked {
            // Set the label to "Hello World!" after the button has been clicked on
            button.setLabel("Hello World!")
        }

        // Create a window and set the title
        val window = ApplicationWindow(app)
        window.setTitle("My GTK App")
        window.setChild(button)

        // Present window
        window.present()
    }

    // Run the application
    app.runApplication()
}

Great! Now we have a button in our app that displays "Press me!". When the button is clicked, it changes its label to "Hello World!".

And that’s it! You’ve just created your first gtk-kn app.