How to Use Kotlin in an Existing Android App?

Question

I have an Android App developed using Java. I now want to start using Kotlin for the same app. Is it possible to use Kotlin and Java side-by-side in an existing app?

Answer 1

Just click ctrl+alt+shift+k to convert your whole app from java to kotlin. And remember to keep your system connected to active internet while you do so because it needs to download the required plugins. I think you'll be good to go after doing this.

Answer 2

To enable Kotlin into your existing Android project. Follow these steps:-

1. Application-level build file:- Add

   apply plugin: 'kotlin-android'

   apply plugin: 'kotlin-android-extensions'

   Add In dependency:- implementation "org.jetbrains.kotlin:kotlin-stdlib-jdk7:$kotlin_version"

2. Project Level build File:-

   dependencies {
       classpath "org.jetbrains.kotlin:kotlin-gradle-plugin:$kotlin_version"
       // NOTE: Do not place your application dependencies here; they belong
       // in the individual module build.gradle files
   }
   

Answer 3

In Android Studio 4, there is no need to manually configure Kotlin for a Java project.

When adding Kotlin files to a Java project, Android Studio will automatically setup Kotlin.

Here is the full procedure:

1. Add any new Android component (Activity for example)

2. Choose Kotlin as the language

3. Android Studio downloads Kotlin

Note: When it finished, it could not resolve the R file in the Kotlin Activity. To fix this, I just hit hovered over the red R in the editor and hit alt-enter.

Finally, in my MainActivity.java:

Intent launchNewIntent = new Intent(this, KotlinActivity.class);
startActivityForResult(launchNewIntent, 0);

This code opens the KotlinActivity from the MainActivity in Java.