Getting familiar with Kotlin

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Getting familiar with Kotlin for Android

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+AkshayChordiya ● Entrepreneur ● Android Developer by heart ● Active community speaker ● Graduated in 2016 Akshay Chordiya @Akshay_Chordiya

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Agenda ● What’s Kotlin? ● Syntax ● Features ● Live Demos ● Issues ● What’s next? ● And finally… questions

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Why Kotlin?

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Kotlin is official language for Android

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What’s otlin?

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

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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

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Syntax Crash course

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

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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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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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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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Lambda Expressions

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// Kotlin mButton.setOnClickListener { // Your logic } Lambda Expressions // Before Java 8 mButton.setOnClickListener(new View.OnClickListener() { public void onClick(View v) { // Your logic } });

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Extension functions

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Usage: Extension Function toast(R.string.magic_spell) snackbar(R.id.content, R.string.magic_spell)

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fun Activity.toast(resId: Int, duration: Int = Toast.LENGTH_SHORT) { Toast.makeText(this, getString(resId), duration).show() } Code: Extension functions

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Higher Order functions

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Usage: Higher Order Functions // We want fragmentManager.load { it.replace(R.id.home_content, MyFragment.newInstance()) } // Old way val trans = fragmentManager.beginTransaction() trans.replace(R.id.home_content, MyFragment.newInstance()) trans.commit()

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Code: Higher Order Functions fun FragmentManager.load(f: (FragmentTransaction) -> Unit) { val transaction = beginTransaction() f(transaction) transaction.commit() } inline fun FragmentManager.load(f: (FragmentTransaction) -> Unit) { val transaction = beginTransaction() f(transaction) transaction.commit() }

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Extension functions with receiver

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Usage: Extension functions with receiver // Previously fragmentManager.load { it.replace(R.id.home_content, MyFragment.newInstance()) } // We want fragmentManager.load { replace(R.id.home_content, MyFragment.newInstance()) }

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Code: Extension functions with receiver inline fun FragmentManager.load(f: FragmentTransaction.() -> Unit) { val transaction = beginTransaction() transaction.f() transaction.commit() }

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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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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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Easter functions

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let block textView?.let { it.text = "Easter" it.textSize = 24F }

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apply block textView?.apply { text = "Easter" textSize = 24F }

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measureTimeMillis function // Java long startTime = System.currentTimeMillis(); // Do your task long executionTime = System.currentTimeMillis() - startTime; System.out.println("Execution Time = " + executionTime + "ms"); // Kotlin val executionTime = measureTimeMillis { // Do your task } println("Execution Time = $executionTime ms")

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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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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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“With Kotlin our code base is shrinked down.”

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“Plenty of app crashes are cut down”

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”Kotlin makes Android development a lot more fun again”

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What’s next?

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Goodbye findViewById

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Data classes

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#ProTips ● Always remember with Kotlin there is always gonna be a better way to do something ● Use Kotlin to Java converter to convert Java files to Kotlin (Shortcut: Ctrl + Alt + Shift + K) ● You can begin writing test cases or data classes for your models to slowly start adding Kotlin to your project

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Questions?

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References ● All the images and logos used are trademarks of respective companies. ● Kotlin Official Website ● Kotlin and Android ● Why Kotlin-ize your Android Development Medium - Akshay Chordiya ● Antonio Leiva Blog ● Android Development with Kotlin — Jake Wharton ● Easter Functions in Kotlin ● Being more productive with Kotlin ● Kotlin - Goodbye findViewById

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Thank you #HappyCoding