04_UsingSharedCodeAndroid.md

Shared Kotlin Code for Android

For this tutorial, we want to minimize Android project changes, so we add an ordinary dependency from that project to the SharedCode project. It is also possible to use the kotlin-multiplatform plugin directly in an Android Gradle project, instead of using the kotlin-android plugin. For more information, please refer to the Multiplatform Projects documentation.

Let's include the dependency from the SharedCode project to the Android project. We need to patch the app/build.gradle file and add the following line in the dependencies { .. } block:

    implementation project(':SharedCode')

We need to assign the id to the TextView control of our activity to access it from the code. Let's patch the app/src/main/res/layout/activity_main.xml file (the name may be different if we changed it in the new project wizard). Select the Text tab at the bottom of the preview to switch it to XML and add several more attributes to the <TextView> element:

        android:id="@+id/main_text"
        android:textSize="42sp"
        android:layout_margin="5sp"
        android:textAlignment="center"

Next, let's add the following line of code to the end of the onCreate method from the MainActivity class in the /app/src/main/java/com/jetbrains/handson/mpp/mobile/MainActivity.kt file, :

findViewById<TextView>(R.id.main_text).text = createApplicationScreenMessage()

You will need to add the import for the android.widget.TextView class. Android Studio will automatically suggest adding the import. Depending on the Android application package, we may also need to add the import for the createApplicationScreenMessage() function too. We should see these two lines at the beginning of the MainActivity.kt file:

import com.jetbrains.handson.mpp.mobile.createApplicationScreenMessage
import android.widget.TextView

Now we have a TextView that will show us the text created by the shared code function createApplicationScreenMessage(). It shows Kotlin Rocks on Android. Let's see how it works by running the Android application.

We can use the step-005 branch of the github.com/kotlin-hands-on/mpp-ios-android repository as a solution for the tasks we've done above. We can also download the archive from GitHub directly or check out the repository and select the branch.

Running the Android Application

Let's click on the App run configuration to get our project running on a real Android device or an emulator.

And now we can see the Application running in the Android emulator: