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
   

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2. @askashdavies
   

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3. @askashdavies
   

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4. pusher.com/state-of-kotlin
   

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5. blog.jetbrains.com/kotlin/2016/02/kotlin-1-0-released-pragmatic-language-for-jvm-and-android/
   

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6. Coroutines
   @askashdavies
   

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7. fun main() {
   GlobalScope.launch {
   delay(1000L)
   println("World!")
   }
   println("Hello,")
   Thread.sleep(2000L)
   }
   // Hello,
   // World!
   @askashdavies
   

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8. fun main() {
   GlobalScope.launch {
   delay(1000L)
   println("World!")
   }
   println("Hello,")
   Thread.sleep(2000L)
   }
   // Hello,
   // World!
   @askashdavies
   

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9. fun main() {
   GlobalScope.launch {
   delay(1000L)
   println("World!")
   }
   println("Hello,")
   Thread.sleep(2000L)
   }
   // Hello,
   // World!
   @askashdavies
   

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10. Coroutine Builders
    @askashdavies
    

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11. Coroutine Builders
    val deferred: Deferred = async { "Hello World!" }
    @askashdavies
    

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12. Coroutine Builders
    val deferred: Deferred = async { "Hello World!" }
    val result: String = deferred.await()
    @askashdavies
    

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13. Coroutine Builders
    val deferred: Deferred = async { "Hello World!" }
    val result: String = deferred.await()
    val job: Job = launch { "Hello World!" }
    @askashdavies
    

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14. Coroutine Builders
    val deferred: Deferred = async { "Hello World!" }
    val result: String = deferred.await()
    val job: Job = launch { "Hello World!" }
    job.join()
    @askashdavies
    

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15. ⚖
    Stability
    @askashdavies
    

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16. @askashdavies
    

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17. @Annotations
    (
    !
    Here be dragons)
    @askashdavies
    

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18. Annotations
    @ExperimentalCoroutinesApi //
    @askashdavies
    

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19. Annotations
    @ExperimentalCoroutinesApi //
    @ObsoleteCoroutinesApi //
    ⚠
    @askashdavies
    

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20. Annotations
    @ExperimentalCoroutinesApi //
    @ObsoleteCoroutinesApi //
    ⚠
    @InternalCoroutinesApi //
    ☠
    @askashdavies
    

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21. !
    Coroutines
    @askashdavies
    

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22. !
    Native first-party library
    @askashdavies
    

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23. !
    Easy-to-use
    @askashdavies
    

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24. !
    suspend fun
    @askashdavies
    

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25. Dispatchers
    @askashdavies
    

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26. !
    History of Android
    @askashdavies
    

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27. Background Processes
    @askashdavies
    

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28. Background Processes
    !
    Runnable / Handler
    @askashdavies
    

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29. Background Processes !
    AsyncTask
    @askashdavies
    

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30. Background Processes
    !
    IntentService
    @askashdavies
    

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31. Background Processes !
    Loader
    @askashdavies
    

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32. Background Processes
    WorkManager
    @askashdavies
    

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33. !
    @askashdavies
    

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34. xkcd.com/927/
    

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35. RxJava to the rescue
    © Ubisoft
    

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36. !
    Reactive
    @askashdavies
    

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37. @askashdavies
    

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38. @askashdavies
    

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39. @askashdavies
    

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40. @askashdavies
    

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41. @askashdavies
    

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42. !
    Asynchronous APIs
    Synchronous APIs
    @askashdavies
    

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43. @askashdavies
    

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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
    

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45. Anchorman: The Legend of Ron Burgundy (DreamWorks Pictures)
    

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46. ⚙
    Hidden complexity
    @askashdavies
    

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47. !
    Hidden gotchas
    @askashdavies
    

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48. !
    Memory footprint
    @askashdavies
    

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49. ⤴
    Steep learning curve
    @askashdavies
    

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51. #RxMustDie
    pca.st/7IJG
    @askashdavies
    

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52. "If all you have is a hammer,
    everything looks like a nail"
    — Abraham Maslow, The Psychology of Science, 1966
    @askashdavies
    

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53. Coroutine Use Cases
    @askashdavies
    

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54. Network Call Handling
    // RxJava2: Single
    fun getUser(): Single = Single.fromCallable { /* ... */ }
    // Coroutines: T
    suspend fun getUser(): User = /* ... */
    @askashdavies
    

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55. Cache Retrieval
    // RxJava2: Maybe
    fun getUser(): Maybe = Maybe.fromCallable { /* ... */ }
    // Coroutines: T?
    suspend fun getUser(): User? = /* ... */
    @askashdavies
    

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56. Background Task Handling
    // RxJava2: Completable
    fun storeUser(user: User): Completable.fromCallable { /* ... */ }
    // Coroutines: Unit
    suspend fun storeUser(user: User) { /* ... */ }
    @askashdavies
    

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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
    

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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
    

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59. ViewModel.viewModelScope
    androidx.lifecycle:lifecycle-viewmodel-ktx:2.1.0-beta01
    @askashdavies
    

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60. Channels
    @askashdavies
    

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61. Roman Elizarov
    Cold flows, hot channels
    Flow.collect {
    it.emit("Hello World!")
    }
    medium.com/@elizarov/cold-flows-hot-channels-d74769805f9
    

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62. ⚙
    RxJava: Complex Business Logic
    @askashdavies
    

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63. Asynchronicity Comparison
    Manuel Vivo (@manuelvicnt)
    medium.com/capital-one-tech/coroutines-and-rxjava-an-asynchronicity-comparison-part-1-asynchronous-programming-e726a925342a
    

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64. Is Coroutines a replacement for RxJava?
    @askashdavies
    

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65. Maybe...
    @askashdavies
    

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66. Not really...
    @askashdavies
    

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67. Should I migrate to Coroutines?
    @askashdavies
    

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68. Probably not...
    @askashdavies
    

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69. "If it ain't broke, don't fix it"
    — Bert Lance, Nation's Business, 1977
    @askashdavies
    

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70. © 2019 Viacom International Inc.
    

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71. Did "you" migrate to Coroutines?
    @askashdavies
    

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72. !
    Yes!
    @askashdavies
    

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73. How could I migrate to Coroutines?
    @askashdavies
    

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74. !
    Migration Policy
    @askashdavies
    

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75. Retrofit Services
    @askashdavies
    

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76. Retrofit2 Coroutines Adapter
    com.jakewharton.retrofit:retrofit2-kotlin-coroutines-adapter:+
    github.com/JakeWharton/retrofit2-kotlin-coroutines-adapter
    

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77. interface UserService {
    @GET("/user")
    fun getUser(): Deferred
    }
    val retrofit = Retrofit.Builder()
    .baseUrl("https://example.com/")
    .addCallAdapterFactory(CoroutineCallAdapterFactory())
    .build()
    GlobalScope.launch {
    val user = retrofit
    .create() // >= 2.5.0
    .getUser()
    .await()
    }
    @askashdavies
    

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78. interface UserService {
    @GET("/user")
    fun getUser(): Deferred
    }
    val retrofit = Retrofit.Builder()
    .baseUrl("https://example.com/")
    .addCallAdapterFactory(CoroutineCallAdapterFactory())
    .build()
    GlobalScope.launch {
    val user = retrofit
    .create() // >= 2.5.0
    .getUser()
    .await()
    }
    @askashdavies
    

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79. Retrofit
    First-party "suspend" support
    github.com/square/retrofit/pull/2886
    

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80. Coroutines RxJava2
    org.jetbrains.kotlinx:kotlinx-coroutines-rx2:+
    @askashdavies
    

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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
    

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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
    

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83. Completable.await()
    GlobalScope.launch {
    Completable
    .complete()
    .await()
    }
    @askashdavies
    

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84. Maybe.await()
    GlobalScope.launch {
    val result: String? = Maybe
    .fromCallable { null as String? }
    .await()
    // result == null
    }
    @askashdavies
    

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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
    

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86. Exceptions?
    @askashdavies
    

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87. Exceptions
    observable.subscribe(
    onSuccess = { it: T -> },
    onError = { it: Throwable -> } // Gotta catch em all!
    )
    launch {
    try {
    doSomethingDangerous()
    } catch(exception: DangerousException) {
    // Specific exception caught!
    }
    }
    @askashdavies
    

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88. Exceptions
    val handler = CoroutineExceptionHandler { _, exception ->
    println("Caught $exception")
    }
    val job = GlobalScope.launch(handler) {
    throw AssertionError()
    }
    join(job)
    // Caught java.lang.AssertionError
    @askashdavies
    

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89. !
    Conclusion
    @askashdavies
    

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90. Cheers!
    !
    bit.ly/rxjava-coroutines-prague
    @askashdavies
    

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