Coroutines on the way! - Speaker Deck

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Coroutines on the way! Armando Picón Android Engineer at Cornershop Inc. @devpicon https://medium.com/@devpicon Using Coroutines in your Android App

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Long running tasks ● Network requests

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Long running tasks ● Network requests ● Database operations

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Long running tasks ● Network requests ● Database operations ● Image processing

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Long running tasks ● Network requests ● Database operations ● Image processing ● ...and more!

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Challenge 1: Execute on a non-UI thread

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Challenge 1: Execute on a non-UI thread Challenge 2: Get informed when the task is done

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Challenge 1: Execute on a non-UI thread Challenge 2: Get informed when the task is done Android solutions ● AsyncTask ● Loaders (deprecated in Android P) ● RxJava ● Thread / HandlerThread / Executor with callbacks

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Threads and callbacks fun login(name, pass) { val thread = Thread(Runnable { requestLogin(name, pass) { result -> show(result) } }) thread.start() }

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Threads and callbacks fun login(name, pass) { val thread = Thread(Runnable { requestLogin(name, pass) { result -> Handler(Looper.getMainLooper()) { show(result) } } }) thread.start()

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Threads and callbacks fun login(name, pass) { requestLogin(name, pass) { result -> show(result) } }

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onDraw onDraw onDraw requestLogin UI Thread fun login(name, pass) { requestLogin(name, pass) { result -> show(result) } }

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onDraw onDraw onDraw requestLogin UI Thread fun login(name, pass) { requestLogin(name, pass) { result -> show(result) } }

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onDraw onDraw onDraw requestLogin UI Thread show onDraw fun login(name, pass) { requestLogin(name, pass) { result -> show(result) } }

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onDraw onDraw onDraw requestLogin UI Thread show onDraw fun login(name, pass) { requestLogin(name, pass) { result -> show(result) } } onDraw onDraw onDraw

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Coroutine = suspendable computation onDraw onDraw onDraw requestLogin UI Thread show onDraw onDraw onDraw onDraw

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Coroutine Write asynchronous code sequentially fun login(name, pass) = launch { val result = requestLogin(name, pass) show(result) }

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Coroutine ~ lightweight thread fun login(name, pass) = launch { val result = requestLogin(name, pass) show(result) }

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fun login(name, pass) = launch(Dispatchers.IO){ val result = requestLogin(name, pass) withContext(Dispatchers.Main) { show(result) } } Coroutine ● Not bound to a speciﬁc thread ● Complete with a result

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fun login(name, pass) { requestLogin(name, pass) { result -> show(result) } } requestLogin Thread show Suspension point

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suspend fun requestLogin( name: String, pass: String ): Result {...}

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suspend fun requestLogin( name: String, pass: String ): Result {...}

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suspend fun requestLogin( name: String, pass: String ): Result {...} Las funciones suspendidas no bloquean el hilo de invocación

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suspend fun requestLogin( name: String, pass: String ): Result = withContext(Dispatchers.IO) { ... }

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Dispatchers.Main ● Main thread ● Use it for: UI operations

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Dispatchers.Default ● Common pool of shared background threads ● Use it for: computing-intensive coroutines Dispatchers.Main ● Main thread ● Use it for: UI operations

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Dispatchers.Default ● Common pool of shared background threads ● Use it for: computing-intensive coroutines Dispatchers.IO ● Shared pool of on-demand created threads ● Use it for: IO-intensive blocking operations Dispatchers.Main ● Main thread ● Use it for: UI operations

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Dispatchers.Default ● Common pool of shared background threads ● Use it for: computing-intensive coroutines Dispatchers.Unconfined ● Doesn’t conﬁne the coroutine to any speciﬁc thread ● Don’t use it in code Dispatchers.IO ● Shared pool of on-demand created threads ● Use it for: IO-intensive blocking operations Dispatchers.Main ● Main thread ● Use it for: UI operations

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suspend fun requestLogin( name: String, pass: String ): Result = withContext(Dispatchers.IO) { ... }

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suspend fun login(name, pass) { val result = requestLogin(name, pass) show(result) } suspend fun requestLogin( name: String, pass: String ): Result = withContext(Dispatchers.IO) { ... }

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suspend fun login(name, pass) { val authToken = authenticate() val result = requestLogin(authToken, name, pass) show(result) } Sequential

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suspend fun login(name, pass) { val authToken = authenticate() val result = requestLogin(authToken, name, pass) show(result) } Data dependencies

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suspend fun login(name, pass) { try { val result = requestLogin(name, pass) show(result) } catch (error: NetworkError){ } } Errors

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Launching and cancelling coroutines Login button pressed Launch coroutine requestLogin Show login status

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Login button pressed Launch coroutine requestLogin Show login status val job = Job() val uiScope = CoroutineScope(Dispatchers.Main + job)

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Login button pressed Launch coroutine requestLogin Show login status val job = Job() val uiScope = CoroutineScope(Dispatchers.Main + job) fun login(username: String, pass: String ) = uiScope.launch { val result = requestLogin(name, pass) show(result) }

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Login button pressed Launch coroutine requestLogin Show login status val job = Job() val uiScope = CoroutineScope(Dispatchers.Main + job) fun login(username: String, pass: String ) = uiScope.launch(Dispatchers.IO) { val result = requestLogin(name, pass) show(result) }

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val job = Job() val uiScope = CoroutineScope(Dispatchers.Main + job) fun login( username: String, pass: String ) = uiScope.launch { val result = requestLogin(name, pass) show(result) } job.cancel()

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Launching and cancelling coroutines Login button pressed Launch coroutine requestLogin Show login status Activity destroyed

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Launching and cancelling coroutines Login button pressed Launch coroutine requestLogin Show login status ViewModel

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Login button pressed Launch coroutine requestLogin Show login status ViewModel fun onCleared() { super.onCleared() job.cancel() }

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class MyViewModel: ViewModel() { val viewModelJob = Job() val uiScope = CoroutineScope(Dispatchers.Main+viewModelJob) fun login( username: String, pass: String ) = uiScope.launch(Dispatchers.IO) { val result = requestLogin(name, pass) show(result) } fun onCleared() { super.onCleared() viewModelJob.cancel() } }

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class MyViewModel: ViewModel() { fun login( username: String, pass: String ) = viewModelScope.launch(Dispatchers.IO) { val result = requestLogin(name, pass) show(result) } }

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● Coroutines ● suspend functions ● Dispatchers ● Launching a coroutine ● Using a coroutine from ViewModels

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● Coroutines ● suspend functions ● Dispatchers ● Launching a coroutine ● Using a coroutine from ViewModels ● Testing coroutines ● Using coroutines with other Jetpack libraries ● Channels

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● Kotlin Official Documentation https://kotlinlang.org/docs/reference/coroutines-overview.html ● Improve app performance with Kotlin Coroutines https://developer.android.com/kotlin/coroutines ● Coroutines in Kotlin 1.3 explained: Suspending functions, contexts, builders and scopes https://antonioleiva.com/kotlin-coroutines/ ● Kotlin Coroutines by Tutorials https://store.raywenderlich.com/products/kotlin-coroutines-by-tutorials

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Ahora es tu turno! codelabs.developers.google.com/ codelabs/ kotlin-coroutines Armando Picón Android Engineer at Cornershop Inc. @devpicon https://medium.com/@devpicon