Android programming with Kotlin

Introduction#

Using Kotlin with Android Studio is an easy task as Kotlin is developed by JetBrains. It is the same company that stands behind IntelliJ IDEA - a base IDE for Android Studio. That is why there are almost none problems with the compatibility.

Remarks#

If you want to learn more about Kotlin Programming Language check out Documentation.

Installing the Kotlin plugin

First, you’ll need to install the Kotlin plugin.

For Windows:

• Navigate to File → Settings → Plugins → Install JetBrains plugin

For Mac:

• Navigate to Android Studio → Preferences → Plugins → Install JetBrains plugin

And then search for and install Kotlin. You’ll need to restart the IDE after this completes.

Configuring an existing Gradle project with Kotlin

You can create a New Project in Android Studio and then add Kotlin support to it or modify your existing project. To do it, you have to:

1. Add dependency to a root gradle file - you have to add the dependency for kotlin-android plugin to a root build.gradle file.

   buildscript {

    repositories {
        jcenter()
    }
    dependencies {
        classpath 'com.android.tools.build:gradle:2.3.1'
        classpath 'org.jetbrains.kotlin:kotlin-gradle-plugin:1.1.2'
    }

   }

   allprojects { repositories { jcenter() } }

   task clean(type: Delete) { delete rootProject.buildDir }

2. Apply Kotlin Android Plugin - simply add apply plugin: 'kotlin-android' to a module build.gradle file.

3. Add dependency to Kotlin stdlib - add the dependency to 'org.jetbrains.kotlin:kotlin-stdlib:1.1.2' to the dependency section in a module build.gradle file.

For a new project, build.gradle file could looks like this:

apply plugin: 'com.android.application'
apply plugin: 'kotlin-android'

android {
    compileSdkVersion 25
    buildToolsVersion "25.0.2"
    defaultConfig {
        applicationId "org.example.example"
        minSdkVersion 16
        targetSdkVersion 25
        versionCode 1
        versionName "1.0"
        testInstrumentationRunner "android.support.test.runner.AndroidJUnitRunner"
    }
    buildTypes {
        release {
            minifyEnabled false
            proguardFiles getDefaultProguardFile('proguard-android.txt'), 'proguard-rules.pro'
        }
    }
}

dependencies {
    compile 'org.jetbrains.kotlin:kotlin-stdlib:1.1.1'
    compile 'com.android.support.constraint:constraint-layout:1.0.2'
    compile 'com.android.support:appcompat-v7:25.3.1'

    androidTestCompile('com.android.support.test.espresso:espresso-core:2.2.2', {
        exclude group: 'com.android.support', module: 'support-annotations'
    })

    testCompile 'junit:junit:4.12'
}

Creating a new Kotlin Activity

1. Click to File → New → Kotlin Activity.
2. Choose a type of the Activity.
3. Select name and other parameter for the Activity.
4. Finish.

Final class could look like this:

import android.support.v7.app.AppCompatActivity
import android.os.Bundle

class MainActivity : AppCompatActivity() {

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main)
    }
}

Converting existing Java code to Kotlin

Kotlin Plugin for Android Studio support converting existing Java files to Kotlin files. Choose a Java file and invoke action Convert Java File to Kotlin File:

Starting a new Activity

fun startNewActivity(){
    val intent: Intent = Intent(context, Activity::class.java)
    startActivity(intent)
}

You can add extras to the intent just like in Java.

fun startNewActivityWithIntents(){
    val intent: Intent = Intent(context, Activity::class.java)
    intent.putExtra(KEY_NAME, KEY_VALUE)  
    startActivity(intent)
}