Coroutines and Flow integration with Android Architecture Components

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Coroutines and Flow with Architecture Components Paolo Rotolo @paolorotolo

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

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Execute on a non-UI thread

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Execute on a non-UI thread Get informed when the task is done

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Execute on a non-UI thread Get informed when the task is done Android solutions ● AsyncTask ● RxJava ● Thread / HandlerThread / Executor with callbacks

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Execute on a non-UI thread Get informed when the task is done Android solutions ● AsyncTask ● RxJava ● Thread / HandlerThread / Executor with callbacks

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Execute on a non-UI thread Get informed when the task is done Android solutions ● AsyncTask ● RxJava ● Thread / HandlerThread / Executor with callbacks

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Execute on a non-UI thread Get informed when the task is done callbacks!!! ● AsyncTask ● RxJava ● Thread / HandlerThread / Executor with Android solutions

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● AsyncTask ● RxJava ● Thread / HandlerThread / Executor with Execute on a non-UI thread Get informed when the task is done callbacks!!!1 Android solutions

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● AsyncTask ● RxJava ● Thread / HandlerThread / Executor with Execute on a non-UI thread Get informed when the task is done callbacks!!!1 Android solutions Deprecated this month!

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● AsyncTask ● RxJava ● Thread / HandlerThread / Executor with Execute on a non-UI thread Get informed when the task is done callbacks!!!1 Android solutions Deprecated this month!

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● AsyncTask ● RxJava ● Thread / HandlerThread / Executor with Execute on a non-UI thread Get informed when the task is done callbacks!!!1 Android solutions Deprecated this month! Need to handle cancellation

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Kotlin Coroutines

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Kotlin Coroutines simple state machine

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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) } } }

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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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When all of the coroutines on the main thread are suspended, the main thread is free to do other work.

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Kotlin Coroutines simple state machine

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Kotlin Coroutines simple state machine suspend keyword

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Kotlin Coroutines simple state machine suspend keyword dispatchers

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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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Used for example by libraries

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Kotlin Coroutines simple state machine suspend keyword dispatchers

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Kotlin Coroutines simple state machine suspend keyword dispatchers structured concurrency

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Kotlin Coroutines simple state machine suspend keyword dispatchers structured concurrency (scope)

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Kotlin Coroutines Hello World

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Kotlin Coroutines World Hello

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// prints Hello, World!

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Kotlin Coroutines simple state machine suspend keyword dispatchers structured concurrency

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Kotlin Coroutines simple state machine suspend keyword dispatchers structured concurrency <3 Andorid

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

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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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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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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 Activity destroyed Coroutine leak

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Coroutines + ViewModel

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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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suspend does not mean background

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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 + Lifecycle

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Coroutines + Lifecycle viewmodel.viewModelScope

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Coroutines + Lifecycle activity.lifecycleScope viewmodel.viewModelScope

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Coroutines + Lifecycle activity.lifecycleScope fragment.lifecycleScope fragment.viewLifecycleOwner viewmodel.viewModelScope

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Coroutines + Lifecycle Examples

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Coroutines + Lifecycle

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Coroutines + Lifecycle React to Lifecycle.State

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Coroutines + LiveData

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Coroutines + LiveData getUser Example

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Coroutines + LiveData LiveData Builder

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Coroutines + LiveData Builder Examples

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Coroutines + LiveData getUser Example

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Coroutines + LiveData LiveData Builder + other LiveData!

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Coroutines + Room

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Coroutines + Room Suspending DAO functions

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Coroutines + Room Behind the scenes

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Runs on IO threads

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Runs on IO threads IO-Thread-1

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Runs on IO threads IO-Thread-1 IO-Thread-2

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Android SQLite transactions are thread confined

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Runs on IO threads IO-Thread-1 IO-Thread-2

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Runs on IO threads IO-Thread-1 IO-Thread-2 Will block until transaction in Io-Thread-1 ends

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Runs on IO threads IO-Thread-1 IO-Thread-2 Will block until transaction in Io-Thread-1 ends DEADLOCK!

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Coroutines + Room Behind the scenes Coroutines executor

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Immediately execute the callable

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Immediately execute the callable Use Room dispatchers

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Immediately execute the callable Use Room dispatchers Free main-safety!

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Coroutines + WorkManager

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Coroutines + WorkManager Types of background work

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Coroutines Coroutines

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Coroutines Coroutines Foregroun dService

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Coroutines Coroutines Foregroun dService WorkManager

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Coroutines + WorkManager Simple Example

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Defaults to Dispatcher.Default

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Coroutines + WorkManager WorkManager -> ForegroundService

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suspendCancellableCoroutine Make callbacks Great again

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suspendCancellableCoroutine Structured Concurrency

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Coroutines + Flows

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Coroutines + Flows Cold stream of data

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Coroutines + Flow Flow builder

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Coroutines + Flow Example: Firebase Realtime

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Questions? Paolo Rotolo @paolorotolo

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Thank you! Paolo Rotolo @paolorotolo