Android Coroutine Recipes

Presentation Source: https://goo.gl/fTP5or

Brief introduction to Kotlin coroutines with practical android samples.

Transcript

1. Android Coroutine Recipes Dmytro Danylyk Atlassian
2. Coroutines simplify asynchronous programming by providing possibility to write code in direct style (sequentially).
3. Thread { code } .start() What we have
4. Thread { code } .start() What we have
5. object MyTask: AsyncTask() { override fun doInBackground { code } override fun onPostExecute { code } } Thread { code } .start() What we have
6. object MyTask: AsyncTask() { override fun doInBackground { code } override fun onPostExecute { code } } Thread { code } .start() What we have
7. object MyTask: AsyncTask() { override fun doInBackground { code } override fun onPostExecute { code } } Observable.just(1,2,3,4) .map { code } .doOnEach { code } .doOnError { code } .subscribe( { onNext }, { onError } ) Thread { code } .start() What we have
8. object MyTask: AsyncTask() { override fun doInBackground { code } override fun onPostExecute { code } } Observable.just(1,2,3,4) .map { code } .doOnEach { code } .doOnError { code } .subscribe( { onNext }, { onError } ) Thread { code } .start() What we have
9. object MyTask: AsyncTask() { override fun doInBackground { code } override fun onPostExecute { code } } Observable.just(1,2,3,4) .map { code } .doOnEach { code } .doOnError { code } .subscribe( { onNext }, { onError } ) Thread { code } .start() What we have
10. What we have What we want
11. What we want fun loadData() = launch { view.showLoading() val result = async { // computation }.await() view.showData(result) view.hideLoading() }
12. Coroutine building blocks
13. coroutine builder coroutine context suspend function builders to launch coroutine coroutine dispatchers mark suspension point
14. withContext() T returns result uncaught exception crash app
15. launch() Job fire and forget uncaught exception crash app withContext() T returns result uncaught exception crash app
16. launch() async() Job Deferred fire and forget returns non-blocking future uncaught exception crash app withContext() T returns result uncaught exception crash app uncaught exception is stored inside the resulting Deferred
17. CoroutineContext UI dispatch execution into Android main thread
18. CoroutineContext UI CommonPool dispatch execution into background thread dispatch execution into Android main thread
19. CoroutineContext UI Unconfined CommonPool dispatch execution into background thread dispatch execution into Android main thread dispatch execution into current thread
20. suspend function suspend fun loadData(): Data fun loadData(listener: Continuation<Data>) transforms to
21. Launch
22. How to launch coroutine // kotlinx.coroutines.experimental.android val uiContext: CoroutineContext = UI // kotlinx.coroutines.experimental val bgContext: CoroutineContext = CommonPool
23. How to launch coroutine private fun loadData() { view.showLoading() val result = dataProvider.provideData() view.showData(result) view.hideLoading() }
24. How to launch coroutine private fun loadData() = launch(uiContext) { view.showLoading() val result = dataProvider.provideData() view.showData(result) view.hideLoading() } parent coroutine
25. How to launch coroutine private fun loadData() = launch(uiContext) { view.showLoading() val result = withContext(bgContext) { dataProvider.provideData() } view.showData(result) view.hideLoading() } child coroutine
26. How to launch coroutine private fun loadData() = launch(uiContext) { view.showLoading() // ui thread val result = withContext(bgContext) { dataProvider.provideData() } // bg view.showData(result) // ui thread view.hideLoading() }
27. Launch two tasks sequentially private fun loadData() = launch(uiContext) { view.showLoading() // ui thread // non ui thread, suspend until task is finished val result1 = withContext(bgContext) { dataProvider.provideData() } // non ui thread, suspend until task is finished val result2 = withContext(bgContext) { dataProvider.provideData() } val result = "$result1 $result2" // ui thread view.showData(result) view.hideLoading() }
28. Launch two tasks sequentially private fun loadData() = launch(uiContext) { view.showLoading() // ui thread // non ui thread, suspend until task is finished val result1 = withContext(bgContext) { dataProvider.provideData() } // non ui thread, suspend until task is finished val result2 = withContext(bgContext) { dataProvider.provideData() } val result = "$result1 $result2" // ui thread view.showData(result) view.hideLoading() }
29. Launch two tasks in parallel private fun loadData() = launch(uiContext) { view.showLoading() // ui thread val task1 = async(bgContext) { dataProvider.provideData() } val task2 = async(bgContext) { dataProvider.provideData() } // non ui thread, suspend until finished val result = "${task1.await()} ${task2.await()}" view.showData(result) // ui thread view.hideLoading() }
30. Launch two tasks in parallel private fun loadData() = launch(uiContext) { view.showLoading() // ui thread val task1 = async(bgContext) { dataProvider.provideData() } val task2 = async(bgContext) { dataProvider.provideData() } // non ui thread, suspend until finished val result = "${task1.await()} ${task2.await()}" view.showData(result) // ui thread view.hideLoading() }
31. Launch a coroutine with a timeout private fun loadData() = launch(uiContext) { view.showLoading() // ui thread // non ui thread, suspend until the task is finished // or return null in 2 sec val result = withTimeoutOrNull(2, TimeUnit.SECONDS) { withContext(bgContext) { dataProvider.provideData() } } view.showData(result) // ui thread view.hideLoading() }
32. Launch a coroutine with a timeout private fun loadData() = launch(uiContext) { view.showLoading() // ui thread // non ui thread, suspend until the task is finished // or return null in 2 sec val result = withTimeoutOrNull(2, TimeUnit.SECONDS) { withContext(bgContext) { dataProvider.provideData() } } view.showData(result) // ui thread view.hideLoading() }
33. Cancellation
34. Сancel a coroutine private var job: Job? = null fun onNextClicked() { job = loadData() } fun onBackClicked() { job?.cancel() } private fun loadData() = launch(uiContext) { // code }
35. Сancel a coroutine private var job: Job? = null fun onNextClicked() { job = loadData() } fun onBackClicked() { job?.cancel() } private fun loadData() = launch(uiContext) { // code }
36. Сancel a coroutine private var job: Job? = null fun onNextClicked() { job = loadData() } fun onBackClicked() { job?.cancel() } private fun loadData() = launch(uiContext) { // code }
37. Error handling
38. try-catch block private fun loadData() = launch(uiContext) { view.showLoading() // ui thread try { val result = withContext(bgContext) { dataProvider.provideData() } view.showData(result) // ui thread } catch (e: IllegalArgumentException) { e.printStackTrace() } view.hideLoading() }
39. Store inside Deferred private fun loadData() = async(uiContext) { view.showLoading() // ui thread val task = async(bgContext) { dataProvider.provideData() } val result = task.await() // non ui thread view.showData(result) // ui thread view.hideLoading() }
40. Store inside Deferred var job: Deferred = loadData() job.invokeOnCompletion { it: Throwable? -> it?.printStackTrace() }
41. Exception handler val exceptionHandler= CoroutineExceptionHandler { _, throwable -> throwable.printStackTrace() } private fun loadData() = launch(uiContext + exceptionHandler) { // code }
42. Return null if exception was thrown /** * return T or null if exception was thrown */ suspend fun <T> Deferred<T>.awaitSafe(): T? = try { await() } catch (e: Exception) { e.printStackTrace() null }
43. Return null if exception was thrown private fun loadData() = launch(uiContext) { val task = async(bgContext) { dataProvider.provideData() } val result = task.awaitSafe() if(result != null) { // success } else { // failure } }
44. Return Result<T> /** * return Result<T> which contain either success or failure */ suspend fun <T> Deferred<T>.awaitResult(): Result<T> = try { Result(success = await(), failure = null) } catch (e: Exception) { Result(success = null, failure = e) } data class Result<out T>(val success: T?, val failure: Exception?)
45. Return Result<T> private fun loadData() = launch(uiContext) { val task = async(bgContext) { dataProvider.provideData() } val (success, failure) = task.awaitResult() if(success != null) { // success T } else { // failure Exception } }
46. Testing
47. Testing: Unconfined context class MainPresenter(val uiContext: CoroutineContext = UI, val bgContext: CoroutineContext = CommonPool) { fun loadData() = launch(uiContext) { ... } }
48. Testing: Unconfined context @Test fun test() { val presenter = MainPresenter(Unconfined, Unconfined) // test presenter.loadData() // verify verify(mockView).showLoading() verify(mockDataProvider).provideData() }
49. Miscellaneous
50. Callback to coroutine fun loadData() { val docRef = db.collection("cities").document("NSW") docRef.get().addOnCompleteListener(OnCompleteListener { task -> if (task.isSuccessful) { // task.result.data } else { // task.exception } }) }
51. Callback to coroutine suspend fun loadData() = suspendCoroutine<Snapshot> { continuation -> val docRef = db.collection("cities").document("NSW") docRef.get().addOnCompleteListener(OnCompleteListener { task -> if (task.isSuccessful) { // task.result.data } else { // task.exception } }) }
52. Callback to coroutine suspend fun loadData() = suspendCoroutine<Snapshot> { continuation -> val docRef = db.collection("cities").document("NSW") docRef.get().addOnCompleteListener(OnCompleteListener { task -> if (task.isSuccessful) { continuation.resume(task.result) } else { continuation.resumeWithException(task.exception) } }) }
53. Callback to coroutine suspend fun loadData() = suspendCoroutine<Snapshot> { continuation -> val docRef = db.collection("cities").document("NSW") docRef.get().addOnCompleteListener(OnCompleteListener { task -> if (task.isSuccessful) { continuation.resume(task.result) } else { continuation.resumeWithException(task.exception) } }) }
54. Coroutine modules // gradle implementation 'io.reactivex.rxjava2:rxjava:2.1.3' implementation 'org.jetbrains.kotlinx:kotlinx-coroutines-rx2:0.19.1' fun loadData() = launch(bgContext) { val result = Single.fromCallable { "Jon Doe" }.await() // suspend }
55. Coroutine modules // reactive implementation 'kotlinx-coroutines-reactive' implementation 'kotlinx-coroutines-reactor' implementation 'kotlinx-coroutines-rx1' implementation 'kotlinx-coroutines-rx2' // integration implementation 'kotlinx-coroutines-guava' implementation 'kotlinx-coroutines-jdk8' implementation 'kotlinx-coroutines-nio' implementation 'kotlinx-coroutines-quasar'
56. Coroutine modules // retrofit 2 interface MyService { @GET("/user") fun getUser(): Deferred<User> // or @GET("/user") fun getUser(): Deferred<Response<User>> }
57. Resources www.github.com/kotlin/kotlinx.coroutines /ui /reactive /integration - documentation - guide to UI programming - guide to reactive streams - guide to future-based libraries
58. googlesamples/android-architecture https://github.com/dmytrodanylyk /android-architecture/tree /todo-mvp-kotlin-coroutines
59. googlesamples/android-architecture
63. Android Coroutines Survey
64. @dmytrodanylyk medium.com/@dmytrodanylyk speakerdeck.com/dmytrodanylyk