mDevCamp: RxJava & Coroutines: A Practical Analysis

Kotlin has taken the Android world by storm, and is quickly becoming the most popular language, with coroutines now stable, does it make sense to replace your RxJava implementations for Coroutines?

Despite the hype, it may not make sense to jump on the bandwagon just yet, with RxJava having already proven its stability and usefulness, and in many cases the comparison between the two frameworks showing that they simply fit different purposes.

In this talk, you can learn how you can utilise the strengths of each framework, how to correctly choose the best solution for the requirements of your project, whether it may be beneficial to migrate or run them concurrently, and how you can start doing so for your project.

Transcript

1. RxJava & Coroutines A Practical Analysis @askashdavies
2. @askashdavies
3. @askashdavies
4. pusher.com/state-of-kotlin
5. blog.jetbrains.com/kotlin/2016/02/kotlin-1-0-released-pragmatic-language-for-jvm-and-android/
6. Coroutines @askashdavies
7. fun main() { GlobalScope.launch { delay(1000L) println("World!") } println("Hello,") Thread.sleep(2000L) } // Hello, // World! @askashdavies
8. fun main() { GlobalScope.launch { delay(1000L) println("World!") } println("Hello,") Thread.sleep(2000L) } // Hello, // World! @askashdavies
9. fun main() { GlobalScope.launch { delay(1000L) println("World!") } println("Hello,") Thread.sleep(2000L) } // Hello, // World! @askashdavies
10. Coroutine Builders @askashdavies
11. Coroutine Builders val deferred: Deferred<String> = async { "Hello World!" } @askashdavies
12. Coroutine Builders val deferred: Deferred<String> = async { "Hello World!" } val result: String = deferred.await() @askashdavies
13. Coroutine Builders val deferred: Deferred<String> = async { "Hello World!" } val result: String = deferred.await() val job: Job = launch { "Hello World!" } @askashdavies
14. Coroutine Builders val deferred: Deferred<String> = async { "Hello World!" } val result: String = deferred.await() val job: Job = launch { "Hello World!" } job.join() @askashdavies
15. ⚖ Stability @askashdavies
16. @askashdavies
17. @Annotations ( ! Here be dragons) @askashdavies
18. Annotations @ExperimentalCoroutinesApi // @askashdavies
19. Annotations @ExperimentalCoroutinesApi // @ObsoleteCoroutinesApi // ⚠ @askashdavies
20. Annotations @ExperimentalCoroutinesApi // @ObsoleteCoroutinesApi // ⚠ @InternalCoroutinesApi // ☠ @askashdavies
21. ! Coroutines @askashdavies
22. ! Native first-party library @askashdavies
23. ! Easy-to-use @askashdavies
24. ! suspend fun @askashdavies
25. Dispatchers @askashdavies
26. ! History of Android @askashdavies
27. Background Processes @askashdavies
28. Background Processes ! Runnable / Handler @askashdavies
29. Background Processes ! AsyncTask @askashdavies
30. Background Processes ! IntentService @askashdavies
31. Background Processes ! Loader<T> @askashdavies
32. Background Processes WorkManager @askashdavies
33. ! @askashdavies
34. xkcd.com/927/
35. RxJava to the rescue © Ubisoft
36. ! Reactive @askashdavies
37. @askashdavies
38. @askashdavies
39. @askashdavies
40. @askashdavies
41. @askashdavies
42. ! Asynchronous APIs Synchronous APIs @askashdavies
43. @askashdavies
44. ! Observable .fromIterable(resourceDraft.getResources()) .flatMap(resourceServiceApiClient::createUploadContainer) .zipWith(Observable.fromIterable(resourceDraft.getResources()), Pair::create) .flatMap(uploadResources()) .toList() .toObservable() .flatMapMaybe(resourceCache.getResourceCachedItem()) .defaultIfEmpty(Resource.getDefaultItem()) .flatMap(postResource(resourceId, resourceDraft.getText(), currentUser, resourceDraft.getIntent())) .observeOn(AndroidSchedulers.mainThread()) .subscribeOn(Schedulers.io()) .subscribe( resource -> repository.setResource(resourceId, resource, provisionalResourceId), resourceUploadError(resourceId, resourceDraft, provisionalResourceId) ); @askashdavies
45. Anchorman: The Legend of Ron Burgundy (DreamWorks Pictures)
46. ⚙ Hidden complexity @askashdavies
47. ! Hidden gotchas @askashdavies
48. ! Memory footprint @askashdavies
49. ⤴ Steep learning curve @askashdavies
51. #RxMustDie pca.st/7IJG @askashdavies
52. "If all you have is a hammer, everything looks like a nail" — Abraham Maslow, The Psychology of Science, 1966 @askashdavies
53. Coroutine Use Cases @askashdavies
54. Network Call Handling // RxJava2: Single<T> fun getUser(): Single<User> = Single.fromCallable { /* ... */ } // Coroutines: T suspend fun getUser(): User = /* ... */ @askashdavies
55. Cache Retrieval // RxJava2: Maybe<T> fun getUser(): Maybe<User> = Maybe.fromCallable { /* ... */ } // Coroutines: T? suspend fun getUser(): User? = /* ... */ @askashdavies
56. Background Task Handling // RxJava2: Completable fun storeUser(user: User): Completable.fromCallable { /* ... */ } // Coroutines: Unit suspend fun storeUser(user: User) { /* ... */ } @askashdavies
57. Thread Handling // RxJava2 getUser() .subscribeOn(Schedulers.io()) .observeOn(AndroidSchedulers.mainThread()) .subscribe { /* Do something */ } // Coroutines launch(Dispatchers.Main) { withContext(Dispatchers.IO) { val user = getUser() /* Do something */ } } @askashdavies
58. Task Cancellation // RxJava2 val disposable: Disposable = Single .create { /* Do something */ } .subscribe { /* Do something else */ } disposable.dispose() // Coroutine val parent: Job = Job() launch(Dispatchers.Main + parent) { /* Do something */ } parent.cancelChildren() @askashdavies
59. ViewModel.viewModelScope androidx.lifecycle:lifecycle-viewmodel-ktx:2.1.0-beta01 @askashdavies
60. Channels @askashdavies
61. Roman Elizarov Cold flows, hot channels Flow.collect { it.emit("Hello World!") } medium.com/@elizarov/cold-flows-hot-channels-d74769805f9
62. ⚙ RxJava: Complex Business Logic @askashdavies
63. Asynchronicity Comparison Manuel Vivo (@manuelvicnt) medium.com/capital-one-tech/coroutines-and-rxjava-an-asynchronicity-comparison-part-1-asynchronous-programming-e726a925342a
64. Is Coroutines a replacement for RxJava? @askashdavies
65. Maybe... @askashdavies
66. Not really... @askashdavies
67. Should I migrate to Coroutines? @askashdavies
68. Probably not... @askashdavies
69. "If it ain't broke, don't fix it" — Bert Lance, Nation's Business, 1977 @askashdavies
70. © 2019 Viacom International Inc.
71. Did "you" migrate to Coroutines? @askashdavies
72. ! Yes! @askashdavies
73. How could I migrate to Coroutines? @askashdavies
74. ! Migration Policy @askashdavies
75. Retrofit Services @askashdavies
76. Retrofit2 Coroutines Adapter com.jakewharton.retrofit:retrofit2-kotlin-coroutines-adapter:+ github.com/JakeWharton/retrofit2-kotlin-coroutines-adapter
77. interface UserService { @GET("/user") fun getUser(): Deferred<User> } val retrofit = Retrofit.Builder() .baseUrl("https://example.com/") .addCallAdapterFactory(CoroutineCallAdapterFactory()) .build() GlobalScope.launch { val user = retrofit .create<UserService>() // >= 2.5.0 .getUser() .await() } @askashdavies
78. interface UserService { @GET("/user") fun getUser(): Deferred<User> } val retrofit = Retrofit.Builder() .baseUrl("https://example.com/") .addCallAdapterFactory(CoroutineCallAdapterFactory()) .build() GlobalScope.launch { val user = retrofit .create<UserService>() // >= 2.5.0 .getUser() .await() } @askashdavies
79. Retrofit First-party "suspend" support github.com/square/retrofit/pull/2886
80. Coroutines RxJava2 org.jetbrains.kotlinx:kotlinx-coroutines-rx2:+ @askashdavies
81. Name Scope Description rxCompletable CoroutineScope Cold completable that starts coroutine on subscribe rxMaybe CoroutineScope Cold maybe that starts coroutine on subscribe rxSingle CoroutineScope Cold single that starts coroutine on subscribe rxObservable ProducerScope Cold observable that starts coroutine on subscribe rxFlowable ProducerScope Cold observable that starts coroutine on subscribe with backpressure support @askashdavies
82. val service: UserService = retrofit.create() // >= 2.5.0 GlobalScope .rxSingle { service.getUser() } .observeOn(AndroidSchedulers.mainThread()) .subscribeOn(Schedulers.io()) .subscribe( { /* Do something with user */ }, { /* Handle error ... probably */ } ) @askashdavies
83. Completable.await() GlobalScope.launch { Completable .complete() .await() } @askashdavies
84. Maybe.await() GlobalScope.launch { val result: String? = Maybe .fromCallable { null as String? } .await() // result == null } @askashdavies
85. Observable.await... val observable = Observable.just(1, 2, 3, 4) // Await first item val item = observable.awaitFirst() // Print each item observable.consumeEach(::println) // Consume all items observable .openSubscription() .consume { println(it.size) } kotlin.github.io/kotlinx.coroutines/kotlinx-coroutines-rx2/kotlinx.coroutines.rx2/io.reactivex.-observable-source/index.html
86. Exceptions? @askashdavies
87. Exceptions observable.subscribe( onSuccess = { it: T -> }, onError = { it: Throwable -> } // Gotta catch em all! ) launch { try { doSomethingDangerous() } catch(exception: DangerousException) { // Specific exception caught! } } @askashdavies
88. Exceptions val handler = CoroutineExceptionHandler { _, exception -> println("Caught $exception") } val job = GlobalScope.launch(handler) { throw AssertionError() } join(job) // Caught java.lang.AssertionError @askashdavies
89. ! Conclusion @askashdavies
90. Cheers! ! bit.ly/rxjava-coroutines-prague @askashdavies