Getting familiar with Kotlin

Introductory talk about Kotlin for Android. In this talk my goal is to teach you something about Kotlin and show how you can use Kotlin to build robust and less crashable apps while having fun developing.

Transcript

1. Getting familiar with Kotlin for Android
2. +AkshayChordiya • Entrepreneur • Android Developer by heart • Active community speaker • Graduated in 2016 Akshay Chordiya @Akshay_Chordiya
3. Agenda • What’s Kotlin? • Syntax • Features • Live Demos • Issues • What’s next? • And finally… questions
4. Why Kotlin?
5. Kotlin is official language for Android
6. What’s otlin?
7. “Kotlin is a new programming language targeting JVM, Android and even JavaScript.”
8. 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
9. Syntax Crash course
10. // String (Implicitly inferred) val spell = "Lumos" // Int val number = 74 // Explicit type var spells: List<String> = ArrayList() Variables
11. “Use val for a value that won’t change” - Immutable val vs var “Use var for something that will vary with time.” - Mutable
12. 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
13. Features
14. Null Safety
15. // Compile time error val spell: String = null // OK val spell: String? = null Declaring null variables
16. // Compile time error var spell: String = "Lumos" spell = null // OK var spell: String? = "Lumos" spell = null Even...
17. // 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
18. // Safe val spell: String? = null val length = spell?.length // Safe with else val length = spell?.length ?: -1 Kotlin-ized way
19. Lambda Expressions
20. // Kotlin mButton.setOnClickListener { // Your logic } Lambda Expressions // Before Java 8 mButton.setOnClickListener(new View.OnClickListener() { public void onClick(View v) { // Your logic } });
21. Extension functions
22. Usage: Extension Function toast(R.string.magic_spell) snackbar(R.id.content, R.string.magic_spell)
23. fun Activity.toast(resId: Int, duration: Int = Toast.LENGTH_SHORT) { Toast.makeText(this, getString(resId), duration).show() } Code: Extension functions
24. Higher Order functions
25. 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()
26. 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() }
27. Extension functions with receiver
28. 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()) }
29. Code: Extension functions with receiver inline fun FragmentManager.load(f: FragmentTransaction.() -> Unit) { val transaction = beginTransaction() transaction.f() transaction.commit() }
30. Smart Cast // Java way if (view instanceof TextView) { ((TextView) view).setText("Avifors"); } // Kotlin way if (view is TextView) { // Smart casting view.text = "Avifors" }
31. String interpolation
32. String interpolation fun sayHello(message: String) { println("Welcome $message") } fun sayTime() { println("Time: ${System.currentTimeMillis()}") }
33. Easter functions
34. let block textView?.let { it.text = "Easter" it.textSize = 24F }
35. apply block textView?.apply { text = "Easter" textSize = 24F }
36. 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")
37. 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") }
38. Issues
39. 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
40. Conclusion
41. “With Kotlin our code base is shrinked down.”
42. “Plenty of app crashes are cut down”
43. ”Kotlin makes Android development a lot more fun again”
44. What’s next?
45. Goodbye findViewById
46. Data classes
47. #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
48. Questions?
49. 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
50. Thank you #HappyCoding