DevFest 2019: Hyderabad - Using Kotlin for Android Dev: a 2-year-retrospective

A look back at 2 years of Kotlin development in Android. We’ll see how Kotlin helped us remove boilerplate, improve readability and how easy it is to adopt Kotlin as a Java developer.

Transcript

1. Using Kotlin for Android Dev: a 2-year-retrospective Kishore Babu Vikram Sharma Android Engineer Android Engineer
2. Agenda - Pros/Cons - Reduction of Code Boilerplate - Highlights - Language Features - Asynchronous Programming
3. Transitioning from Java to Kotlin Pros: 1. Reduces a lot of boilerplate code 2. Compatible within existing Android Projects 3. Modern language features 4. Faster to compile on moderns JVMs 5. First Class Citizen status for Android SDK Cons: 1. Learning Curve 2. Best Practices - Work In Progress 3. Less developers available. 4. (Relatively) Smaller community
4. Reducing Boilerplate 1. Null Safety 2. Data Classes 3. kotlin-stdlib higher order methods 4. Objects
5. Up to Speed: Kotlin Basics class Address { var name: String = "Holmes" var street: String = "Baker" var city: String = "London" var state: String? = null var zip: String = "123456" }
6. Up to Speed: Kotlin Basics val x: Int = 20 val y: Double = 21.5
7. Up to Speed: Kotlin Basics listOfInts.filter { it > 0 } // this literal is of type '(it: Int) -> Boolean'
8. Up to Speed: Extension Functions fun View?.isVisible(): Boolean = this?.visibility == View.VISIBLE txtView.isVisible() txtView.visibility == View.VISIBLE
9. Null Safety - Safe Calls val a = "Kotlin" val b: String? = null println(b?.length)
10. Null Safety - Safe Calls Bob?.department?.head?.name
11. Data Classes
16. data class User(val name: String, val age: Int)
17. @Parcelize data class User(val name: String, val age: Int): Parcelable
18. kotlin-stdlib higher order methods: Examples 1. .let 2. .apply 3. .with 4. .run 5. .also
19. .let{} webView.settings?.let { setting -> setting.javaScriptEnabled = true setting.domStorageEnabled = true setting.userAgentString = “mobile_app_webview” }
20. .apply{} val intent = Intent() intent.action = intentAction intent.data=Uri.parse(intentData) //Using apply function ( apply return this i.e Intent in this case) Intent() .apply { action = intentAction } .apply { data = Uri.parse(intentData)
21. Sequences val numbersSequence = sequenceOf("four", "three", "two", "one")
22. Sequences
23. Objects object CarFactory { val cars = mutableListOf<Car>() fun makeCar(horsepowers: Int): Car { val car = Car(horsepowers) cars.add(car) return car } }
24. Asynchronous Programming - Coroutines
25. Ways to do asynchronous programming • Threads • AsyncTasks • Callbacks • RxJava • Coroutines
26. Suspending functions
27. Suspending functions suspend fun longTimeTakingFunction():Int{ repeat(100){ Thread.sleep(100) } return 10 }
28. Coroutine builders
29. • launch{} -> returns Job • async {} -> returns DeferedJob • runBlocking<Unit>{} -> returns explicitly given return type
30. Coroutine builders and Scope: fun someViewModelFunction(){ GlobalScope.launch{ val someInt = longProcessingFunction() print(someInt.toString()) // will be printed later } println("end of viewmodel function") //will be printed first } suspend fun longTimeTakingFunction():Int{ repeat(100){ delay(100) //suspended function } return 10 }
31. Custom scope and jobs: val job = SupervisorJob() val customScope: CoroutineScope = CoroutineScope(job + Dispatchers.Default) fun onDestroy() { job.cancel() // will cancel all child coroutines Or scope.cancel()//will cancel all the jobs started from this scope }
32. Coroutine Context and Dispatchers : fun someViewModelFunction(){ GlobalScope.launch(Dispatchers.Default){ val someInt = longProcessingFunction() print(someInt.toString()) } doSomeOtherTask() } Dispatchers.IO -> For IO tasks Dispatchers.Default -> For computational tasks. Dispatchers.Main -> For UI tasks
33. Concurrency with Async: “async” is another coroutine builder like “launch” which returns DefferedJob instead of Job
34. suspend fun getRandomNumber(): Int { delay(1000) return (0..10).random() } fun sum() { customScope.launch { val a = getRandomNumber() val b = getRandomNumber() print("${a + b}") //takes 2014 millis } }
35. fun sum() { customScope.launch { val a = getRandomNumber() val b = getRandomNumber() print("${a + b}") //takes 2014 millis } } fun asyncSum() { customScope.launch { val a = async { getRandomNumber() } val b = async { getRandomNumber()} print("${a.await() + b.await()}") //takes 1014 millis } }
36. Exception Handling
37. fun getUserInfo() { try { viewModelScope.launch { throw IOException() } } catch (ex: Exception) { println("Exception occured") // will be called } }
38. fun getUserInfo() { try { viewModelScope.async { throw IOException() } } catch (ex: Exception) { println("Exception occured") // will never be called } }
39. fun getUserInfo() { try { viewModelScope.async { throw IOException() }.await() } catch (ex: Exception) { println("Exception occured") // will be called } }
40. Exception thrown by child job try { viewModelScope.launch { try { launch { throw IOException() } } catch (ex: Exception) { println("Exception Child job")// control will never reach here } } } catch (ex: Exception) { println("Exception Parent job")// will always be called }
41. Exception thrown by child job try { viewModelScope.launch { try { async { //relying on user to await() throw IOException() } } catch (ex: Exception) { println("Exception Child job")// control will never reach here } } } catch (ex: Exception) { println("Exception Parent job")// will always be called }
42. Exception thrown by child job try { viewModelScope.launch { try { val deferedJob = async { throw IOException() } deferedJob.await() } catch (ex: Exception) { println("Exception Child job") // called first } } } catch (ex: Exception) { println("Exception Parent job") // called later }
43. CoroutineExceptionHandler val handler = CoroutineExceptionHandler { _, throwable -> println("Exception occurred $throwable") } viewModelScope.launch(handler) { throw Exception("This exception will be printed") } viewModelScope.async(handler) { throw Exception("This exception will not be printed") }
44. Wrapping Up • All new projects are Kotlin, by default. • Most recent projects are using Coroutines
45. Resources • Kotlinlang.org • Kotlin Codelabs • Kotlin DSL samples
46. Code • https://github.com/vikram2330/GDGKotlinSample • http://bit.ly/devfest-kotlin
47. Slides • http://bit.ly/devfest-kotlin-slides