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.

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
}
  1. Apply Kotlin Android Plugin - simply add apply plugin: 'kotlin-android' to a module build.gradle file.
  1. 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'
}

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:

enter image description here

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.

enter image description here

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)
    }
}

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.

installing the Kotlin plugin

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)
}
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