LiveData with Coroutines and Flow

View 와 ViewModel 에서 Coroutine을 보다 손쉽게 사용할 수 있는 extension property에 대해서 알아보고, LiveData coroutine builder도 알아보겠습니다.

References

LiveData with Coroutines and Flow (Android Dev Summit '19)

https://www.youtube.com/watch?v=B8ppnjGPAGE&t=416s

LiveData Overview

https://developer.android.com/topic/libraries/architecture/livedata

Use Kotlin coroutines with Architecture components

https://developer.android.com/topic/libraries/architecture/coroutines

Easy Coroutines in Android: viewModelScope

https://medium.com/androiddevelopers/easy-coroutines-in-android-viewmodelscope-25bffb605471

Lessons learnt using Coroutines Flow in the Android Dev Summit 2019 app

https://medium.com/androiddevelopers/lessons-learnt-using-coroutines-flow-4a6b285c0d06

iosched adssched2019 branch
https://github.com/google/iosched/tree/adssched2019

CodeLab : Advanced Coroutines with Kotlin Flow and LiveData

https://codelabs.developers.google.com/codelabs/advanced-kotlin-coroutines/index.html?index=..%2F..index#0

Testing Coroutines on Android (Android Dev Summit '19)

https://www.youtube.com/watch?v=KMb0Fs8rCRs&t=11s

Cold flows, hot channels

https://medium.com/@elizarov/cold-flows-hot-channels-d74769805f9

Simple design of Kotlin Flow

https://medium.com/@elizarov/simple-design-of-kotlin-flow-4725e7398c4c

Kotlin Flows and Coroutines

https://medium.com/@elizarov/kotlin-flows-and-coroutines-256260fb3bdb

Transcript

1. Android Dev Summit 2019 extended Seoul LiveData with Coroutines and Flow ੉਋୸ kakaopay
2. dependencies { implementation knowledgebase('Android Architecture Component') // LiveData, ViewModel implementation 'androidx.lifecycle:lifecycle-viewmodel-ktx:2.1.0' // viewModelScope implementation 'androidx.lifecycle:lifecycle-runtime-ktx:2.2.0-rc03' // lifecycleScope implementation 'androidx.lifecycle:lifecycle-livedata-ktx:2.2.0-rc03' // liveData coroutine builder = CoroutineLiveData // Flow ... Summary
3. Layered architecture
4. Android Dev Summit 2019 extended Seoul Layered architecture View ViewModel LiveData Repository suspend fun DataSource suspend fun UseCase suspend fun Presentation Domain Data
5. Android Dev Summit 2019 extended Seoul LiveData View ViewModel LiveData UseCase suspend fun Repository suspend fun DataSource suspend fun
6. Android Dev Summit 2019 extended Seoul DataSource suspend fun Coroutine View ViewModel LiveData UseCase suspend fun Repository suspend fun
7. Android Dev Summit 2019 extended Seoul
8. Launching coroutines
9. class MyViewModel : ViewModel(), CoroutineScope { override val coroutineContext: CoroutineContext get() = SupervisorJob() + Dispatchers.Main fun doSomething() { launch { // do something } } } ViewModel
10. class MyViewModel : ViewModel(), CoroutineScope { override val coroutineContext: CoroutineContext get() = SupervisorJob() + Dispatchers.Main override fun onCleared() { cancel() // coroutineContext.cancel() } } ViewModel
11. class MyViewModel : ViewModel() { fun doAnything() { GlobalScope.launch { // do anything } } } ViewModel
12. androidx.lifecycle: lifecycle-viewmodel-ktx:2.1.0
13. class MyViewModel : ViewModel() { init { viewModelScope.launch { // do something } } } ViewModel with viewModelScope
14. ViewModel with viewModelScope val ViewModel.viewModelScope: CoroutineScope get() { val scope: CoroutineScope? = this.getTag(JOB_KEY) if (scope != null) { return scope } return setTagIfAbsent(JOB_KEY, CloseableCoroutineScope( SupervisorJob() + Dispatchers.Main )) }
15. internal class CloseableCoroutineScope( context: CoroutineContext ) : Closeable, CoroutineScope { override val coroutineContext: CoroutineContext = context override fun close() { coroutineContext.cancel() } ViewModel with viewModelScope
16. ViewModel with viewModelScope public abstract class ViewModel { final void clear() { mCleared = true; if (mBagOfTags != null) { synchronized (mBagOfTags) { for (Object value : mBagOfTags.values()) { closeWithRuntimeException(value); } } } onCleared(); }
17. class MyViewModel : ViewModel() { override fun onCleared() { viewModelScope.launch { // do something } } } ViewModel with viewModelScope
18. androidx.lifecycle: lifecycle-runtime-ktx:2.2.0-rc03
19. class MyActivity : AppCompatActivity() { override fun onCreate(savedInstanceState: Bundle?) { super.onCreate(savedInstanceState) lifecycleScope.launch { // do something } } } Activities & Fragments with lifecycleScope
20. val LifecycleOwner.lifecycleScope: LifecycleCoroutineScope get() = lifecycle.coroutineScope val Lifecycle.coroutineScope: LifecycleCoroutineScope get() { ... val newScope = LifecycleCoroutineScopeImpl( this, SupervisorJob() + Dispatchers.Main.immediate ) ... } Activities & Fragments with lifecycleScope
21. class MyActivity : AppCompatActivity() { override fun onDestroy() { super.onDestroy() lifecycleScope.launch { // do something } } } Activities & Fragments with lifecycleScope
22. class MyActivity : AppCompatActivity() { override fun onCreate(savedInstanceState: Bundle?) { super.onCreate(savedInstanceState) lifecycleScope.launch { // do something } lifecycleScope.launchWhenResumed { // do something } } } Activities & Fragments with lifecycleScope
23. Activities & Fragments with lifecycleScope class MyActivity : AppCompatActivity() { override fun onCreate(savedInstanceState: Bundle?) { ... lifecycleScope.launch { lifecycleScope.launchWhenResumed { repeat(100) { delay(30) textView.text = (it + 1).toString() } }
24. launch launchWhenResumed VS
25. class MyFragment : Fragment() { init { lifecycleScope.launchWhenCreated { // do something } lifecycleScope.launchWhenStarted { // do something } } } Activities & Fragments with lifecycleScope
26. Application scope or WorkManager https://www.youtube.com/watch?v=B8ppnjGPAGE&t=910s Application
27. LiveData coroutine builder
28. ViewModel + LiveData class MyViewModel : ViewModel() { private val _result = MutableLiveData<String>() val result: LiveData<String> = _result init { viewModelScope.launch { val computationResult = doComputation() _result.value = computationResult } } }
29. ViewModel + LiveData class MyViewModel : ViewModel() { private val _result = MutableLiveData<String>() val result: LiveData<String> = _result init { viewModelScope.launch(Dispatchers.IO) { val computationResult = doComputation() _result.postValue(computationResult) } } }
30. androidx.lifecycle: lifecycle-livedata-ktx:2.2.0-rc03
31. liveData coroutine builder class MyViewModel : ViewModel() { val result = liveData { emit(doComputation()) } }
32. liveData coroutine builder fun <T> liveData(...): LiveData<T> = CoroutineLiveData(context, timeoutInMs, block) internal class CoroutineLiveData<T>( ... ) : MediatorLiveData<T>() { init { ... val scope = CoroutineScope( Dispatchers.Main.immediate + context + supervisorJob) ... } }
33. Dispatchers.Main.immediate ?
34. liveData coroutine builder class MyViewModel : ViewModel() { val result = liveData(Dispatchers.IO) { emit(doComputation()) } }
35. liveData coroutine builder class MyViewModel : ViewModel() { val result = liveData { emit(doComputation()) emitSource(repo.fetchSomething()) } } class MyRepository { fun fetchSomething(): LiveData<String> { ...
36. liveData coroutine builder class MyViewModel : ViewModel() { private val itemId = MutableLiveData<Long>() val item = itemId.switchMap { liveData { emit(fetchItem(it)) } } }
37. LiveData coroutine builder + with flow
38. class MyDataSource { private val weather: String get() = listOf("Sunny", "Rainy", "Cloudy").shuffled().first() fun fetchWeather(): LiveData<String> = liveData { fun fetchWeatherFlow() = flow { while (true) { delay(2_000) emit(weather) } } } Data Source
39. emit N values // LiveData -> LiveData val currentWeather: LiveData<String> = dataSource.fetchWeather()
40. emit N values // LiveData -> LiveData val currentWeather: LiveData<String> = dataSource.fetchWeather() // flow -> LiveData val currentWeatherFlow: LiveData<String> = liveData { dataSource.fetchWeatherFlow().collect { emit(it) } }
41. emit N values // LiveData -> LiveData val currentWeather: LiveData<String> = dataSource.fetchWeather() // flow -> LiveData val currentWeatherFlow: LiveData<String> = dataSource.fetchWeatherFlow().asLiveData()
42. emit 1 + emit N // LiveData -> LiveData val currentWeather: LiveData<String> = liveData { emit(LOADING_STRING) emitSource(dataSource.fetchWeather()) }
43. emit 1 + emit N // LiveData -> LiveData val currentWeather: LiveData<String> = liveData { emit(LOADING_STRING) emitSource(dataSource.fetchWeather()) } // flow -> LiveData val currentWeatherFlow: LiveData<String> = liveData { emit(LOADING_STRING) emitSource( dataSource.fetchWeatherFlow().asLiveData() ) }
44. emit 1 + emit N // LiveData -> LiveData val currentWeather: LiveData<String> = liveData { emit(LOADING_STRING) emitSource(dataSource.fetchWeather()) } // flow -> LiveData val currentWeatherFlow: LiveData<String> = dataSource.fetchWeatherFlow() .onStart { emit(LOADING_STRING) } .asLiveData()
45. Transformation // LiveData -> LiveData val currentWeather: LiveData<String> = dataSource.fetchWeather().switchMap { liveData { emit(heavyTransformation(it)) } }
46. Transformation // LiveData -> LiveData val currentWeather: LiveData<String> = dataSource.fetchWeather().switchMap { liveData { emit(heavyTransformation(it)) } } // flow -> LiveData val currentWeatherFlow: LiveData<String> = dataSource.fetchWeatherFlow() .map { heavyTransformation(it) } .asLiveData()
47. cancelling Coroutine LiveData
48. val currentWeather: LiveData<String> = dataSource.fetchWeatherFlow().map { it.toUpperCase() }.onStart { emit("ON START") }.asLiveData() cancelling CoroutineLiveData
49. fun <T> Flow<T>.asLiveData( context: CoroutineContext = EmptyCoroutineContext, timeoutInMs: Long = DEFAULT_TIMEOUT ): LiveData<T> = liveData(context, timeoutInMs) { collect { emit(it) } } fun <T> liveData( context: CoroutineContext = EmptyCoroutineContext, timeoutInMs: Long = DEFAULT_TIMEOUT, @BuilderInference block: suspend LiveDataScope<T>.() -> Unit ): LiveData<T> = CoroutineLiveData(context, timeoutInMs, block) cancelling CoroutineLiveData
50. internal class CoroutineLiveData<T>( ... ) : MediatorLiveData<T>() { init { ... blockRunner = BlockRunner( ... ) } override fun onInactive() { super.onInactive() blockRunner?.cancel() } } cancelling CoroutineLiveData
52. internal class BlockRunner<T>( … ) { fun cancel() { ... cancellationJob = scope.launch(Dispatchers.Main.immediate) { delay(timeoutInMs) if (!liveData.hasActiveObservers()) { ... runningJob?.cancel() runningJob = null } } … cancelling CoroutineLiveData
53. val currentWeather: LiveData<String> = dataSource.fetchWeatherFlow().map { it.toUpperCase() }.onStart { emit("ON START") }.asLiveData() }.asLiveData(parentJob) }.asLiveData(viewModelScope.coroutineContext) cancelling CoroutineLiveData
54. ViewModel, Repository, DataSource patterns
56. CodeLab
58. Testing
59. Testing Coroutines on Android (Android Dev Summit '19)
60. Android Dev Summit 2019 extended Seoul References • LiveData with Coroutines and Flow (Android Dev Summit '19) https://www.youtube.com/watch?v=B8ppnjGPAGE&t=416s • LiveData Overview https://developer.android.com/topic/libraries/architecture/livedata • Use Kotlin coroutines with Architecture components https://developer.android.com/topic/libraries/architecture/coroutines • Easy Coroutines in Android: viewModelScope https://medium.com/androiddevelopers/easy-coroutines-in-android-viewmodelscope-25bffb605471 • Lessons learnt using Coroutines Flow in the Android Dev Summit 2019 app https://medium.com/androiddevelopers/lessons-learnt-using-coroutines-flow-4a6b285c0d06 • iosched adssched2019 branch : https://github.com/google/iosched/tree/adssched2019
61. Android Dev Summit 2019 extended Seoul References • CodeLab : Advanced Coroutines with Kotlin Flow and LiveData https://codelabs.developers.google.com/codelabs/advanced-kotlin-coroutines/index.html?index=.. %2F..index#0 • Testing Coroutines on Android (Android Dev Summit '19) https://www.youtube.com/watch?v=KMb0Fs8rCRs&t=11s • Cold flows, hot channels https://medium.com/@elizarov/cold-flows-hot-channels-d74769805f9 • Simple design of Kotlin Flow https://medium.com/@elizarov/simple-design-of-kotlin-flow-4725e7398c4c • Kotlin Flows and Coroutines https://medium.com/@elizarov/kotlin-flows-and-coroutines-256260fb3bdb
62. Thank you