Kotlin for all the Droids

This talk will be around Kotlin being a first class language for Android. How it makes Android code much cleaner, better to maintain and introduces many new concepts that Android developers could not do in Java. This talk will be showing Android developers how to take their code to the next level.

Transcript

1. Kotlin for all the Droids Peter-John Welcome @pjapplez Mobile Developer
2. Google announced Kotlin will be an official language for Android
3. Kotlin Was born in 2011 by JetBrains Team • Modern • Expressive • Magical • Powerful • Concise • Extensible https://en.wikipedia.org/wiki/Kotlin_(programming_language) 100% Interoperable with Java
4. Why Kotlin over Java? • Java is very verbose. • Java Code is error prone with all its anonymous inner classes. • Java lacks modern language features. • Nullability issues.
5. Language Features
6. var/val var name : String = "Peter" name = "John" val surname = "Welcome" surname = "Johnson" // val can’t be reassigned
7. Number one reason Android Apps Crash?
8. Null Pointer Exception
9. Nullability var name : String = "Peter" name = null // null can’t be a value on a non-null String var surname : String? = "Peter" surname = null val otherName = surname ?: "" // Elvis operator ( ?? in other languages)
10. Classes
11. Classes class User { private val name: String private val surname : String constructor(name : String , surname: String) { this .name = name this.surname = surname } } var user = User( surname = "Welcome", name = "Peter") // named arguments
12. Data class @Parcelize data class Human (private var name: String, val age: Int) : Parcelable //copy, equal, hashcode, toString var human = Human("Peter",27)
13. Sealed Classes sealed class Result<out T>{ data class Success<out T> (val value : T) : Result<T>() data class Error(val error : MyError) : Result<MyError>() }
14. Sealed Classes fun <T>resultsFromService(result : Result<T>) : String { when (result) { is Result.Success -> "${result.value} World" is Result.Error -> return result.error.toString() } return "" } resultsFromService(Result.Success("Hello"))
15. Functions
16. First class citizens
17. High order functions
18. Functions fun hello(){ print("Hello") } val functionAsVariable = hello() val greetingPeter = fun (func : (name :String) -> String ) : String = func("Peter") greetingPeter { "Hello $it" }
19. Extension functions
20. Extension functions infix fun Int.add (value : Int) = this + value val result = 1.add(1) val result = 1 add 1 //Extension function fun <T> Observable<T>.applySchedulers() : Observable<T> = this.subscribeOn(Schedulers.io()).observeOn(AndroidSchedulers.mainThread()) //Usage disposable.add(this.viewModel.createPlant(Plant(name = "Best Plant Ever")).applySchedulers().subscribe ())
21. Function Literals with Receiver
22. Function Literals with Receiver inline fun SharedPreferences.edit(action: SharedPreferences.Editor.() -> Unit) { val editor = edit() editor.action() editor.apply() } getSharedPreferences("cache", Context.MODE_PRIVATE).edit { putString("username", "Peter") }
23. Delegates
24. Delegates var name : String by lazy { "Peter-John" } There are many more in the standard library and you can make your own. var surname : String by Delegates.observable("Welcome") { property, oldValue, newValue -> print(oldValue) // Welcome print(newValue) // Welcoming } surname = "Welcoming"
25. Async Programming
26. AsyncTasks class doAsyncTask(textView: TextView) : AsyncTask<Unit, Unit, String>() { val innerTextView: TextView? = textView override fun doInBackground(vararg params: Unit?): String? { try { ... return data } catch (e: Exception) { return null } } override fun onPostExecute(result: String?) { super.onPostExecute(result) innerTextView?.text = JSONObject(result).toString() } }
27. AsyncTasks
28. RxJava disposable.add(viewModel.fetchDashboardPlants() .applySchedulers() .subscribe({ //onNext: ... }, { error -> //onError }) ) fun <T> Observable<T>.applySchedulers() : Observable<T> = this.subscribeOn(Schedulers.io()).observeOn(AndroidSchedulers.mainThread())
29. Coroutines internal val background = newFixedThreadPoolContext(2, "background") launch (background) { val result = resultsFromService(Result.Success("Hello")) launch(UI) { this.textView.text = result } } // The async await way val someLongRunningTask = async<String>(CommonPool) { return@async "" }.await()
30. How has Kotlin improved Android development?
31. https://kotlinlang.org/docs/kotlin-docs.pdf Case studies
32. Android KTX
33. https://github.com/android/android-ktx Android KTX
34. Android KTX • Animator functions • Content • Time operations • OS • Utils (arrays, primitive types, File operations) • Database Cursor • Views, ViewGroup and Transitions • Graphics • And More https://medium.com/exploring-android/exploring-ktx-for-android-13a369795b51
35. Android KTX //Normal Kotlin version view.viewTreeObserver.addOnPreDrawListener( object : ViewTreeObserver.OnPreDrawListener { override fun onPreDraw(): Boolean { viewTreeObserver.removeOnPreDrawListener(this) actionToBeTriggered() return true } }) //AndroidKTX version view.doOnPreDraw { actionToBeTriggered() }
36. Android KTX animator.addListener { handleAnimation(it) } animator.addListener( onEnd = {}, onStart = {}, onCancel = {}, onRepeat = {} )
37. https://github.com/android/kotlin-guides Android Kotlin Style guide
38. https://developer.android.com/guide/components/activities/intro-activities.html#kotlin Community Android Developer website • KotlinConf ( https://kotlinconf.com/ ) • Kotlin Weekly ( http://kotlinweekly.net/ ) • Android Weekly ( http://androidweekly.net/ ) • Kotlin Slack ( http://slack.kotlinlang.org/ ) • Talking Kotlin - Podcast ( http://talkingkotlin.com/ )
39. Books
40. Links • https://www.youtube.com/playlist?list=PLQ176FUIyIUY6UK1cgVsbdPYA3X5 WLam5 • https://kotlinlang.org/docs/reference/android-overview.html • https://medium.com/exploring-android • http://talkingkotlin.com/ • https://github.com/android/android-ktx • https://github.com/android/kotlin-guides • https://developer.android.com/kotlin/index.html • https://medium.com/@pjwelcome
41. Thanks! Contact me: https://medium.com/@pjwelcome @pjapplez pjwelcome@gmail.com Peter-johnwelcome.co.za https://github.com/pjwelcome