Kotlin in ActionA concise way to code Android Projects

in a smarter way

© 2016

What is Kotlin?...it’s just another language…

● Created by Jetbrains

● Statically typed

● Lightweight

● Running on JVM

Old fashion Android Coding● Android supports only Java6(ish)

● The verbosity of Java is annoying (i.e. a lot of boilerplate code)

● The Billion Dollar Mistake (aka Null Reference)

Why Kotlin?● Concise: Reduce the boilerplate code, no ceremonies, no decorations

● Safe: It’s a Null Safety language

● Versatile: Write Android, Front end and Server Side applications

● Interoperable: Write Kotlin and Java code in the same project

Kotlin Language

The Language

fun getAvg(a: Int, b: Int): Int { return (a + b) / 2}

fun getAvg(a: Int, b: Int) = (a + b) / 2

val number: Int = 0val stringArray = ArrayList<String>()var average: Float? = null

Extension FunctionsSimply way to extend a class adding new functions

fun Context.toast(message: CharSequence, duration: Int = Toast.LENGTH_SHORT) { Toast.makeText(this, message, duration).show()}…toast("Hello Folks!")

Extension Functionsfun MutableList<Int>.swap(index1: Int, index2: Int) { val tmp = this[index1] // 'this' corresponds to the list this[index1] = this[index2] this[index2] = tmp}

fun <T> MutableList<T>.swap(index1: Int, index2: Int) { val tmp = this[index1] // 'this' corresponds to the list this[index1] = this[index2] this[index2] = tmp}

Extension Functions

fun ImageView.loadImage(url: String) {

Glide.with(context) .load(url) .diskCacheStrategy(DiskCacheStrategy.ALL) .fitCenter() .into(this)}

Lambda Expression Syntax

val sum : (Int, Int) -> Int = {x: Int, y: Int -> x + y}

val sum = { x: Int, y: Int -> x + y }

val notEmpty: (String) -> Boolean = { !it.isEmpty() }

val notEmpty = { it: String -> !it.isEmpty() }

Higher-Order Functions and LambdasA function that takes functions as parameters, or returns a function

fun getId(id: Int, func: (Int) -> String): String {

return func(id)}

val hereMyID = getId(101478, { x -> "Here My Id: $x" })

Lazy Initialization

var mySdk : Sdk? = null

mySdk = Sdk()

Sdk mySdk = null;

mySdk = new Sdk();

Java Kotlin

lateinit var mySdk : Sdk

mySdk = Sdk()

Lazy InitializationKotlin

class JavaClass { Sdk mySdk;

final Sdk getSdk() { if (mySdk == null) { mySdk = new Sdk(); } return mySdk; }}

val mySdk : Sdk by lazy { getSdk() }

protected fun getSdk() = Sdk()

Java

val mySdk : Sdk by lazy { Sdk() }

Kotlin Android Extensions LibraryJava: recyclerView = (RecyclerView)findViewById(R.id.recycler_view);

Kotlin: recyclerView = findViewById(R.id.recycler_view) as RecyclerView

Kotter Knife: val recyclerView by bindView<RecyclerView>(R.id.recycler_view)

Extensions Library: just import import kotlinx.android.synthetic.main.my_layout.*

Android Extensions LibraryPros:

● Compile time check

● No casts

● Less error prone.

● No libraries in your build.gradle (less methods!) (Butterknife is 342)

● Can import Views from different flavors

AnkoAnko is a DSL (Domain-specific language) written in Kotlin to simplify the programmatically creation of UI.

Much more:

● Intents● Fragments● Services● Configuration qualifiers● Dialogs and toasts● Asynchronous tasks● Logging● Using SQLite● Extending Anko

val intent = Intent(this, javaClass<SomeActivity>())intent.putExtra("id", 5)intent.putExtra("name", "John")startActivity(intent)

startActivity(Intent(this, SomeActivity::class.java).putExtra("id", 5).putExtra("name", "John"))

startActivity<SomeActivity>("id" to 5, "name" to "John")

Anko - IntentsKotlin i.e. 1

Kotlin i.e. 2

Kotlin with Anko

async { // Long background task uiThread { result.text = "Done" }}

val executor = Executors.newScheduledThreadPool(4)async(executor) { // Some task}

Anko - AsyncTask

class SomeActivity : Activity(), AnkoLogger { private fun someMethod() { info("London is the capital of Great Britain") debug(5) // .toString() method will be executed warn(null) // "null" will be printed

wtf(“Oh, No!”) }}

Anko - Logger

Kotlin Configuration

Configuration● JDK7● Android Studio

Preferences -> Plugin - > Install JetBrain Plugins -> Kotlin

ConfigurationCreate a New Project

Tools -> Kotlin -> Configure Kotlin in Project

build.gradle (Module :app)buildscript {

dependencies {

classpath "org.jetbrains.kotlin:kotlin-gradle-plugin:$kotlin_version"}

}

apply plugin: 'com.android.application'

apply plugin: 'kotlin-android'

apply plugin: 'kotlin-android-extensions'

android {………

}

Kotlin by Examples

API: http://thecatapi.comEndpoint: /api/images/get?format=xml&results_per_page=10

The Amazing Android App for Funny Cats

<response><data><images><image><url>http://24.media.tumblr.com/tumblr_llees8B3V31qbe5pxo1_500.jpg

</url><id>9j6</id><source_url>http://thecatapi.com/?id=9j6</source_url>

</image><image><url>http://25.media.tumblr.com/tumblr_m4g9rvBP441qz6jrko1_400.jpg

</url><id>a1k</id><source_url>http://thecatapi.com/?id=a1k</source_url>

</image></images>

</data></response>

Ciro Rizzo Enzo BelliSenior Application Developer @QVC Senior Android Developer @YoYoWallet

@JackRixhttp://www.cirorizzo.net/

@enzobelli

© 2016

https://kotlinlang.org/

https://github.com/cirorizzo/KShowshttps://github.com/cirorizzo/JShows