Kotlin-ize your Android Development 

Akshay Chordiya +AkshayChordiya ● Indie Android Developer ● Graduated in 2016 Who am I? 

● Why another language? ● Problems with Java - Android ● What’s Kotlin ● Features ● Issues ● And finally… questions Agenda 

Why another language? 

“Java is old, too much verbose and don’t forget the infamous NullPointerException“ 

Problems with Java -- Android ● Stuck at Java 6-7 ● Restrictions to add functionality to Platform APIs ● Android loves Inheritance ● Lots of boilerplate ● Ceremony of APIs ● Android loves to throw nulls ● Need of Modern coding style ● And so much more…. 

What’s otlin? 

“Kotlin is a new programming language targeting JVM, Android and even JavaScript.” 

Kotlin ● Modern & Statically typed ● Targets JVM, Android and JavaScript ● Works everywhere where Java works ● 100% interoperable with Java™ ● Combines Object Oriented and Functional features ● Made by good folks at JetBrains ● Open source 

Big Players using Kotlin 

Little bit about the Syntax 

// String (Implicitly inferred) val spell = "Lumos" // Int val number = 74 // Explicit type var spells: List = ArrayList() Variables // String (Implicitly inferred) val spell = "Lumos" // Int val number = 74 // Explicit type var spells: List = new ArrayList() 

“Use val for a value that won’t change” - Immutable val vs var “Use var for something that will vary with time.” - Mutable 

fun add(a: Int, b: Int): Int { return a + b } Functions fun add(a: Int, b: Int) = a + b fun add(a: Int = 0, b: Int = 0) = a + b 

Features 

Null Safety 

// Compile time error val spell: String = null // OK val spell: String? = null Declaring null variables 

// Compile time error var spell: String = "Lumos" spell = null // OK var spell: String? = "Lumos" spell = null Even... 

// Compile time error val spell: String? = null val length = spell.length // OK val spell: String? = null if (spell != null) { // Smart cast val length = spell.length } Null Safety 

// Safe val spell: String? = null val length = spell?.length // Safe with else val length = spell?.length ?: -1 Kotlin-ized way 

String interpolation 

String interpolation fun sayHello(message: String) { println("Welcome $message") } fun sayTime() { println("Time: ${System.currentTimeMillis()}") } 

Lambda Expressions 

mButton.setOnClickListener { // Your logic } Lambda Expressions mButton.setOnClickListener { // Using the view parameter v -> v.visibility = GONE } 

fun consume(f: () -> Unit): Boolean { f() return true } Higher Order Functions inline fun consume(f: () -> Unit): Boolean { f() return true } 

Extension functions 

fun View.visible() { visibility = VISIBLE } fun View.visible() { visibility = VISIBLE } fun String.isEmail(): Boolean { return Patterns.EMAIL_ADDRESS.matcher(this).matches() } fun String.isEmail(): Boolean { return Patterns.EMAIL_ADDRESS.matcher(this).matches() } Example: Extension functions 

val email = "[email protected]" if (email.isEmail()) { // Do login } Usage: Extension Function textView.visible() 

inline fun SharedPreferences. edit(func: SharedPreferences.Editor.() -> Unit) { val editor = edit() editor.func() editor.apply() } inline fun SharedPreferences. edit(func: SharedPreferences.Editor.() -> Unit) { val editor = edit() editor.func() editor.apply() } Extension + Higher Order functions // Usage val pref = PreferenceManager.getDefaultSharedPreferences(context) pref.edit{ putString("first_name", "Akshay") putString("last_name", "Chordiya") remove("last_name") } 

Smart Cast // Java way if (view instanceof TextView) { ((TextView) view).setText("Avifors"); } // Kotlin way if (view is TextView) { // Smart casting view.text = "Avifors" } 

Ninja functions 

let block textView?.let { textView.visible() } 

apply block textView?.apply { visible() } 

with function with(textView) { text = "Accio" visible() } val textView = with(TextView(this)) { text = "Accio" visible() this } 

when expression override fun onOptionsItemSelected (item: MenuItem) = when (item.itemId) { R.id.action_about -> consume { startActivity(Intent( baseContext, AboutActivity:: class.java)) } else -> super.onOptionsItemSelected(item) } 

Issues 

Issues ● Slightly increased build time ● Adds Dex Count (6K) to your app ● No static methods and variables. The same functionality can be achieved using companion objects ● Difficulty in coding in functional paradigm 

Conclusion 

“With Kotlin our code base is shrinked down.” 

“Plenty of app crashes are cut down” 

”Kotlin makes Android development a lot more fun again” 

What’s next? 

Questions? 

References ● All the images and logos used are trademarks of respective companies. ● Kotlin Official Website ● Why Kotlin-ize your Android Development Medium - Akshay Chordiya ● Antonio Leiva Blog ● Why You Should Start Using Kotlin to Supercharge Your Android Development in 2017 ● Android Development with Kotlin — Jake Wharton ● Kotlin - Android document by Square ● Droidcon NYC 2016 - Kotlin in Production ● Being more productive with Kotlin 

Thank you #HappyCoding