Introduction to Kotlin Workshop

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Introduction to Kotlin - Android Workshop

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+AkshayChordiya ● Indie Android Developer ● Serial blogger and speaker ● Graduated in 2016 Akshay Chordiya @aky

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● A Computer program writer ● Love writing tech blogs and contributing back to community ● Mentor college graduates and professional who wants to go for mobile app development ● Visit Hardik Trivedi GitHub Blog

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

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Why Kotlin?

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Kotlin is official language for Android

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Problems with Java -- Android ● Stuck at Java 6-7; Java 8 has now come to rescue ● Restrictions to add functionality to Platform APIs ● Android loves Inheritance ● Lots of boilerplate ● Ceremony of APIs ● Android loves to throw nulls ● Lack of Modern coding style ● And so much more….

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What’s otlin?

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

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Big Players using Kotlin

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Little bit about the Syntax

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// 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()

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

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val max = if (a > b) a else b Control Flow val max = if (a > b) { a } else { b }

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when (x) { in 1..10 -> print("x is in") !in 10..20 -> print("x is outside") else -> print("To infinity & beyond") } when expression when { x.isOdd() -> print("x is Odd") x.isEven() -> print("x is Even") else -> print("x is different") }

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// De-structured for ((index, value) in avengers.withIndex()) { println("$value at $index") } Loops val avengers = listOf("Iron Man","Thor") // For-each for (avenger in avengers) { println(avenger) }

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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

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Class // Define class Spell(name: String = "") // Usage val spell = Spell()

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class Spell(name: String = "") { var code: Int = 0 constructor(name: String, code: Int): this(name) { this.code = code } } Class

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class Spell(name: String = "") { var code: Int = 0 init { code = generateCode(name) } } Class

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Data Class data class Spell(var name: String = "")

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Singleton in Kotlin object MagicWand { var spell: String? = null } // Class is initialized MagicWand.spell = "Alohomora" // Prints the value println(MagicWand.spell)

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Features

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Null Safety

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

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

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// 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

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

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String interpolation

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

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Lambda Expressions

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

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

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Extension functions

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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

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

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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") }

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

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Ninja functions

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

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apply block textView?.apply { visible() }

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

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Let’s code!

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Issues

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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

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Conclusion

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What’s next?

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Questions?

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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

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Thank you