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RxJava & Coroutines A Practical Analysis Droidcon Lisbon ! @askashdavies

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@askashdavies

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@askashdavies

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pusher.com/state-of-kotlin

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

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Coroutines @askashdavies

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

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

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

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Coroutine Builders @askashdavies

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

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

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

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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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⚖ Stability @askashdavies

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@askashdavies

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@Annotations ( ! Here be dragons) @askashdavies

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Annotations @ExperimentalCoroutinesApi // @askashdavies

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Annotations @ExperimentalCoroutinesApi // @FlowPreview // ⚠ @askashdavies

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Annotations @ExperimentalCoroutinesApi // @FlowPreview // ⚠ @ObsoleteCoroutinesApi // ⚠ @askashdavies

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Annotations @ExperimentalCoroutinesApi // @FlowPreview // ⚠ @ObsoleteCoroutinesApi // ⚠ @InternalCoroutinesApi // ☠ @askashdavies

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Annotations @Experimental @askashdavies

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! Coroutines @askashdavies

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! Native first-party library @askashdavies

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! Easy-to-use @askashdavies

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! suspend fun @askashdavies

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Dispatchers » Default » IO » Main » Android (Main Thread Dispatcher) » JavaFx (Application Thread Dispatcher) » Swing (Event Dispatcher Thread) » Unconfined @askashdavies

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! History of Android @askashdavies

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Background Processes @askashdavies

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Background Processes ! Runnable / Handler @askashdavies

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Background Processes ! AsyncTask @askashdavies

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Background Processes ! IntentService @askashdavies

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Background Processes ! Loader @askashdavies

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Background Processes WorkManager @askashdavies

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! @askashdavies

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xkcd.com/927/

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RxJava to the rescue @askashdavies

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⛓ Chained operations @askashdavies

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⬆ ⬇ Abstract threading @askashdavies

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! Reactive @askashdavies

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@askashdavies

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@askashdavies

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@askashdavies

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@askashdavies

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@askashdavies

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! Asynchronous APIs Synchronous APIs @askashdavies

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@askashdavies

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! 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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Anchorman: The Legend of Ron Burgundy (DreamWorks Pictures)

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⚙ Hidden complexity @askashdavies

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! Hidden gotchas @askashdavies

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! Memory footprint @askashdavies

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⤴ Steep learning curve @askashdavies

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@askashdavies

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#RxMustDie pca.st/7IJG @askashdavies

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

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Coroutine Use Cases @askashdavies

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

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

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

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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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! FlatMap // RxJava2 getUser() .flatMap { doSomethingWithUser(it) } .subscribeOn(Schedulers.computation()) .observeOn(AndroidSchedulers.mainThread()) .subscribe { /* Do something else */ } // Coroutines launch(Dispatchers.Main) { val user = getUser() val smth = doSomethingWithUser(user) /* Do something else */ } @askashdavies

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Callback Consumption // RxJava2 fun getSingle(): Single = Single.create { emitter -> doSomethingAsync(object: Callback { override fun onComplete(result: T) = emitter.onSuccess(result) override fun onException(exception: Exception) = emitter.onError(exception) }) } // Coroutines suspend fun getCoroutine() : T = suspendCoroutine { continuation -> doSomethingAsync(object : Callback { override fun onComplete(result: T) = continuation.resume(result) override fun onException(exception: Exception) = continuation.resumeWithException(exception) }) } @askashdavies

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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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! Backpressure @askashdavies

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! Backpressure launch { channel.send("Hello") } @askashdavies

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ViewModel.viewModelScope androidx.lifecycle:2.1.0 @askashdavies

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Channels @askashdavies

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

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Flow ! Observable.create { emitter: ObservableEmitter -> emitter.onNext("Hello") emitter.onNext("World") } @askashdavies

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Flow ! flow { collector: FlowCollector -> collector.emit("Hello") collector.emit("World") } @askashdavies

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Flow ! flow { emit("Hello world") } .onEach { delay(500) } .map { it.length } .collect { println("Length: $it") } @askashdavies

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Testing @Test fun testFoo() = runBlockingTest { val actual = foo() // ... } suspend fun foo() { delay(1_000) // ... } github.com/Kotlin/kotlinx.coroutines/tree/master/kotlinx-coroutines-test

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runBlockingTest » Auto-advancing of time ⏱⏩ » Explicit time control # » Eager execution of launch or async » Pause, manually advance, and restart execution » Report uncaught exceptions as test failures @askashdavies

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⚙ RxJava: Complex Business Logic @askashdavies

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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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Is Coroutines a replacement for RxJava? @askashdavies

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Maybe... @askashdavies

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Should I migrate to Coroutines? @askashdavies

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Probably not... @askashdavies

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

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© 2019 Viacom International Inc.

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Did "you" migrate to Coroutines? @askashdavies

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@askashdavies

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How could I migrate to Coroutines? @askashdavies

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! Migration Policy @askashdavies

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Retrofit Services @askashdavies

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Retrofit 2.6.0 Built-in suspend support github.com/square/retrofit/blob/master/CHANGELOG.md#version-260-2019-06-05

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interface UserService { @GET("/user") suspend fun getUser(): User } GlobalScope.launch { val user = retrofit .create() // >= 2.5.0 .getUser() } @askashdavies

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

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

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

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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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Exceptions @askashdavies

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! Conclusion @askashdavies

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Cheers! ! @askashdavies