Android Coroutine Recipes

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Android Coroutine Recipes Dmytro Danylyk Atlassian

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Coroutines simplify asynchronous programming by providing possibility to write code in direct style (sequentially).

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Thread { code } .start() What we have

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Thread { code } .start() What we have

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object MyTask: AsyncTask() { override fun doInBackground { code } override fun onPostExecute { code } } Thread { code } .start() What we have

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object MyTask: AsyncTask() { override fun doInBackground { code } override fun onPostExecute { code } } Thread { code } .start() What we have

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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

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What we have What we want

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What we want fun loadData() = launch { view.showLoading() val result = async { // computation }.await() view.showData(result) view.hideLoading() }

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Coroutine building blocks

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coroutine builder coroutine context suspend function builders to launch coroutine coroutine dispatchers mark suspension point

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withContext() T returns result uncaught exception crash app

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launch() Job fire and forget uncaught exception crash app withContext() T returns result uncaught exception crash app

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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

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CoroutineContext UI dispatch execution into Android main thread

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CoroutineContext UI CommonPool dispatch execution into background thread dispatch execution into Android main thread

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CoroutineContext UI Unconfined CommonPool dispatch execution into background thread dispatch execution into Android main thread dispatch execution into current thread

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suspend function suspend fun loadData(): Data fun loadData(listener: Continuation) transforms to

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Launch

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How to launch coroutine // kotlinx.coroutines.experimental.android val uiContext: CoroutineContext = UI // kotlinx.coroutines.experimental val bgContext: CoroutineContext = CommonPool

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How to launch coroutine private fun loadData() { view.showLoading() val result = dataProvider.provideData() view.showData(result) view.hideLoading() }

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How to launch coroutine private fun loadData() = launch(uiContext) { view.showLoading() val result = dataProvider.provideData() view.showData(result) view.hideLoading() } parent coroutine

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How to launch coroutine private fun loadData() = launch(uiContext) { view.showLoading() val result = withContext(bgContext) { dataProvider.provideData() } view.showData(result) view.hideLoading() } child coroutine

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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() }

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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() }

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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() }

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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() }

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Cancellation

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Сancel a coroutine private var job: Job? = null fun onNextClicked() { job = loadData() } fun onBackClicked() { job?.cancel() } private fun loadData() = launch(uiContext) { // code }

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Сancel a coroutine private var job: Job? = null fun onNextClicked() { job = loadData() } fun onBackClicked() { job?.cancel() } private fun loadData() = launch(uiContext) { // code }

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Сancel a coroutine private var job: Job? = null fun onNextClicked() { job = loadData() } fun onBackClicked() { job?.cancel() } private fun loadData() = launch(uiContext) { // code }

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Error handling

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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() }

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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() }

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Store inside Deferred var job: Deferred = loadData() job.invokeOnCompletion { it: Throwable? -> it?.printStackTrace() }

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Exception handler val exceptionHandler= CoroutineExceptionHandler { _, throwable -> throwable.printStackTrace() } private fun loadData() = launch(uiContext + exceptionHandler) { // code }

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Return null if exception was thrown /** * return T or null if exception was thrown */ suspend fun Deferred.awaitSafe(): T? = try { await() } catch (e: Exception) { e.printStackTrace() null }

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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 } }

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Return Result /** * return Result which contain either success or failure */ suspend fun Deferred.awaitResult(): Result = try { Result(success = await(), failure = null) } catch (e: Exception) { Result(success = null, failure = e) } data class Result(val success: T?, val failure: Exception?)

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Return Result private fun loadData() = launch(uiContext) { val task = async(bgContext) { dataProvider.provideData() } val (success, failure) = task.awaitResult() if(success != null) { // success T } else { // failure Exception } }

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Testing

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Testing: Unconfined context class MainPresenter(val uiContext: CoroutineContext = UI, val bgContext: CoroutineContext = CommonPool) { fun loadData() = launch(uiContext) { ... } }

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Testing: Unconfined context @Test fun test() { val presenter = MainPresenter(Unconfined, Unconfined) // test presenter.loadData() // verify verify(mockView).showLoading() verify(mockDataProvider).provideData() }

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Miscellaneous

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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 } }) }

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Callback to coroutine suspend fun loadData() = suspendCoroutine { continuation -> val docRef = db.collection("cities").document("NSW") docRef.get().addOnCompleteListener(OnCompleteListener { task -> if (task.isSuccessful) { // task.result.data } else { // task.exception } }) }

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Callback to coroutine suspend fun loadData() = suspendCoroutine { 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) } }) }

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Callback to coroutine suspend fun loadData() = suspendCoroutine { 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) } }) }

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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 }

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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'

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Coroutine modules // retrofit 2 interface MyService { @GET("/user") fun getUser(): Deferred // or @GET("/user") fun getUser(): Deferred> }

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Resources www.github.com/kotlin/kotlinx.coroutines /ui /reactive /integration - documentation - guide to UI programming - guide to reactive streams - guide to future-based libraries

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googlesamples/android-architecture https://github.com/dmytrodanylyk /android-architecture/tree /todo-mvp-kotlin-coroutines