Android Suspenders

So you’ve read the Coroutines guide and you’re ready to start using them in your Android app to coroutines? Great!

This talk will focus on the best practices of using coroutines in your app, including how to handle lifecycle changes with Architecture Components, integration with background job processing, and moving away from RxJava.

Transcript

1. SUSPENDERS ANDROID @chrisbanes
2. ANDROID SUSPENDERS chris.banes.me/suspenders
3. Android’s main thread
4. Android’s main thread measure + layout draw View inflation and many more things
5. ms 60Hz 16 Android’s main thread
6. 12 ms Android’s main thread 90Hz
7. ms 120Hz 8 Android’s main thread
9. ASYNC ALL THE THINGS
10. How do we do that?
11. Executors AsyncTask How do we do that?
12. Loaders Executors AsyncTask How do we do that?
13. Future Executors Loaders How do we do that?
14. Libraries Loaders Future How do we do that?
15. WorkManager Future Libraries How do we do that?
16. Coroutines Libraries Coroutines How do we do that?
17. Coroutines Libraries Coroutines So why use ?
18. What does your typical mobile app do?
19. CRUD What does your typical mobile app do?
20. C R U D reate ead pdate elete What does your typical mobile app do?
21. Sync What does your typical mobile app do?
22. Sync What does your typical mobile app do?
23. So why coroutines? Scale on limited hardware Easier development model Great for I/O tasks
24. Tivi github.com/chrisbanes/tivi
25. kotlinx-coroutines-core -android -rx2
26. -core -android -rx2 jars: 774KB
27. -core -android -rx2 jars: 774KB apk: 499KB 3260 method refs
28. -core -android -rx2 jars: 774KB apk: 499KB 3260 method refs r8: 113KB 1208 method refs
29. -core -android -rx2 jars: 774KB apk: 499KB 3260 method refs r8: 113KB 1208 method refs r8
 optimized: 99KB 834 method refs
30. -keepclassmembernames class kotlinx.** { volatile <fields>; }
31. ANDROID SUSPENDERS Creating routines
32. override suspend fun updateShow(showId: Long) { val localResult = localShowStore.getShow(showId) val result1 = remoteSource1.getShow(showId) val result2 = remoteSource2.getShow(showId) val merged = mergeShow(localResult, result1, result2) localShowStore.saveShow(merged) }.
33. override suspend fun updateShow(showId: Long) { val localResult = localShowStore.getShow(showId) val result1 = remoteSource1.getShow(showId) val result2 = remoteSource2.getShow(showId) val merged = mergeShow(localResult, result1, result2) localShowStore.saveShow(merged) }. 1
34. override suspend fun updateShow(showId: Long) { val localResult = localShowStore.getShow(showId) val result1 = remoteSource1.getShow(showId) val result2 = remoteSource2.getShow(showId) val merged = mergeShow(localResult, result1, result2) localShowStore.saveShow(merged) }. 1 2
35. override suspend fun updateShow(showId: Long) { val localResult = localShowStore.getShow(showId) val result1 = remoteSource1.getShow(showId) val result2 = remoteSource2.getShow(showId) val merged = mergeShow(localResult, result1, result2) localShowStore.saveShow(merged) }. 1 2 3
36. override suspend fun updateShow(showId: Long) { val localResult = localShowStore.getShow(showId) val result1 = remoteSource1.getShow(showId) val result2 = remoteSource2.getShow(showId) val merged = mergeShow(localResult, result1, result2) localShowStore.saveShow(merged) }.
37. override suspend fun updateShow(showId: Long) { val localResult = localShowStore.getShow(showId) val result1 = remoteSource1.getShow(showId) val result2 = remoteSource2.getShow(showId) val merged = mergeShow(localResult, result1, result2) localShowStore.saveShow(merged) }. 1 2 3 Runs in 1.2 seconds
38. override suspend fun updateShow(showId: Long) { val localDeferred = async {
 localShowStore.getShow(showId)
 } val remoteDeferred1 = async { remoteSource1.getShow(showId) } val remoteDeferred2 = async { remoteSource2.getShow(showId) } 
 val localResult = localDeferred.await() val result1 = remoteDeferred1.await() val result2 = remoteDeferred2.await() val merged = mergeShow(localResult, result1, result2) localShowStore.saveShow(merged) }.
39. override suspend fun updateShow(showId: Long) { val localDeferred = async {
 localShowStore.getShow(showId)
 } val remoteDeferred1 = async { remoteSource1.getShow(showId) } val remoteDeferred2 = async { remoteSource2.getShow(showId) } 
 val localResult = localDeferred.await() val result1 = remoteDeferred1.await() val result2 = remoteDeferred2.await() val merged = mergeShow(localResult, result1, result2) localShowStore.saveShow(merged) }.
40. override suspend fun updateShow(showId: Long) { val localDeferred = async {
 localShowStore.getShow(showId)
 } val remoteDeferred1 = async { remoteSource1.getShow(showId) } val remoteDeferred2 = async { remoteSource2.getShow(showId) } 
 val localResult = localDeferred.await() val result1 = remoteDeferred1.await() val result2 = remoteDeferred2.await() val merged = mergeShow(localResult, result1, result2) localShowStore.saveShow(merged) }.
41. override suspend fun updateShow(showId: Long) { val localDeferred = async {
 localShowStore.getShow(showId)
 } val remoteDeferred1 = async { remoteSource1.getShow(showId) } val remoteDeferred2 = async { remoteSource2.getShow(showId) } 
 val localResult = localDeferred.await() val result1 = remoteDeferred1.await() val result2 = remoteDeferred2.await() val merged = mergeShow(localResult, result1, result2) localShowStore.saveShow(merged) }.
42. override suspend fun updateShow(showId: Long) { val localDeferred = async {
 localShowStore.getShow(showId)
 } val remoteDeferred1 = async { remoteSource1.getShow(showId) } val remoteDeferred2 = async { remoteSource2.getShow(showId) } 
 val localResult = localDeferred.await() val result1 = remoteDeferred1.await() val result2 = remoteDeferred2.await() val merged = mergeShow(localResult, result1, result2) localShowStore.saveShow(merged) }.
43. override suspend fun updateShow(showId: Long) { val localDeferred = async {
 localShowStore.getShow(showId)
 } val remoteDeferred1 = async { remoteSource1.getShow(showId) } val remoteDeferred2 = async { remoteSource2.getShow(showId) } 
 val localResult = localDeferred.await() val result1 = remoteDeferred1.await() val result2 = remoteDeferred2.await() val merged = mergeShow(localResult, result1, result2) localShowStore.saveShow(merged) }. Runs in 0.8 second
44. How do we use them on Android?
45. class ShowDetailsViewModel: ViewModel() { val showRepository: ShowRepository = // ... val state: LiveData<ViewState> init { refresh() } private fun refresh() { launch { showRepository.updateShow(showId) // update view state } } }
46. class ShowDetailsViewModel: ViewModel() { val showRepository: ShowRepository = // ... val state: LiveData<ViewState> init { refresh() } private fun refresh() { launch { showRepository.updateShow(showId) // update view state } } }
47. class ShowDetailsViewModel: ViewModel() { val showRepository: ShowRepository = // ... val state: LiveData<ViewState> init { refresh() } private fun refresh() { launch { showRepository.updateShow(showId) // update view state } } }
48. class ShowDetailsViewModel: ViewModel() { val showRepository: ShowRepository = // ... val state: LiveData<ViewState> init { refresh() } private fun refresh() { launch { showRepository.updateShow(showId) // update view state } } }
49. class ShowDetailsViewModel: ViewModel() { val showRepository: ShowRepository = // ... val state: LiveData<ViewState> init {• refresh() }. private fun refresh() {• launch {• showRepository.updateShow(showId) // update view state }. }. }.
50. Jobs
51. class ShowDetailsViewModel: ViewModel() { private fun refresh() { launch { showRepository.updateShow(showId) // update view state }. }. }.
52. class ShowDetailsViewModel: ViewModel() { private fun refresh() { val job = launch { showRepository.updateShow(showId) // update view state }. }. }.
53. class ShowDetailsViewModel: ViewModel() { private fun refresh() { val job = launch { showRepository.updateShow(showId) // update view state }. // can call job.cancel() }. }.
54. class ShowDetailsViewModel: ViewModel() { private var updateShowJob: Job? = null private fun refresh() { val job = launch { showRepository.updateShow(showId) // update view state }. // can call job.cancel() }. }.
55. class ShowDetailsViewModel: ViewModel() { private var updateShowJob: Job? = null private fun refresh() { updateShowJob = launch { showRepository.updateShow(showId) // update view state }. // can call job.cancel() }. }.
56. class ShowDetailsViewModel: ViewModel() { private var updateShowJob: Job? = null private fun refresh() { updateShowJob = launch { showRepository.updateShow(showId) // update view state }. }. }.
57. class ShowDetailsViewModel: ViewModel() { private var updateShowJob: Job? = null private fun refresh() { updateShowJob = launch { showRepository.updateShow(showId) // update view state }. }. override fun onCleared() { updateShowJob ?.cancel() } }.
58. class ShowDetailsViewModel: ViewModel() { private var updateShowJob: Job? = null private var updateEpisodesJob: Job? = null private fun refresh() { updateShowJob = launch { showRepository.updateShow(showId) // update view state }. updateShowJob = launch { ... } }. override fun onCleared() { updateShowJob ?.cancel() updateEpisodesJob ?.cancel() } }.
59. class ShowDetailsViewModel: ViewModel() { private var updateShowJob: Job? = null private var updateEpisodesJob: Job? = null private var updateCastJob: Job? = null private fun refresh() { updateShowJob = launch { showRepository.updateShow(showId) // update view state }. updateShowJob = launch { ... } updateCastJob = launch { ... } }. override fun onCleared() { updateShowJob ?.cancel() updateEpisodesJob ?.cancel() updateCastJob ?.cancel() } }.
60. Coroutines can have a parent-child relationship
61. Coroutines can have a parent-child relationship Expressed via Jobs (in a context)
62. class ShowDetailsViewModel: ViewModel() { val showRepository: ShowRepository = // ... val state: LiveData<ViewState> private val job = Job() init {• refresh() }. private fun refresh() {• launch(parent = job) {• showRepository.updateShow(showId) // update view state }. }.
63. class ShowDetailsViewModel: ViewModel() { val showRepository: ShowRepository = // ... val state: LiveData<ViewState> private val job = Job() init { refresh() }. private fun refresh() { launch(parent = job) { showRepository.updateShow(showId) // update view state }. }. override onCleared() {
64. private val job = Job() init { refresh() }. private fun refresh() { launch(parent = job) { showRepository.updateShow(showId) // update view state }. }. override onCleared() { job.cancel() } .. }.
65. private val job = Job() init { refresh() }. private fun refresh() { launch(parent = job) { showRepository.updateShow(showId) // update view state }. }. override onCleared() { job.cancel() } } ..
66. private val job = Job() init { refresh() }. private fun refresh() { launch(parent = job) { showRepository.updateShow(showId) // update view state }. }. override onCleared() { job.cancel() } } ..
67. private val job = Job() init { refresh() }. private fun refresh() { launch(parent = job) { showRepository.updateShow(showId) // update view state }. }. override onCleared() { job.cancel() } } .. launch is now scoped to the lifetime of the ViewModel
68. Scopes
69. private val job = Job() init { refresh() }. private fun refresh() { launch(parent = job) { showRepository.updateShow(showId) // update view state }. }. override onCleared() { super.onCleared() job.cancel() } } .. Explicit
70. launch(parent = job) { } suspend fun updateShow(showId: Long) {
 val local = async {
 localShowStore.getShow(showId)
 }}
 val remote = async { remoteSource.getShow(showId) }} val merged = mergeShow(local.await(), remote.await()) localShowStore.saveShow(merged) }.
71. launch(parent = job) { } suspend fun updateShow(showId: Long) {
 val local = async {
 localShowStore.getShow(showId)
 }}
 val remote = async { remoteSource.getShow(showId) }} val merged = mergeShow(local.await(), remote.await()) localShowStore.saveShow(merged) }. New coroutines No parent Suspended job.cancel() Cancelled
72. init { refresh() }. private fun refresh() { launch(parent = job) { showRepository.updateShow(showId) // update view state }. }. override onCleared() { Deprecated in v0.26 async too
73. New! v0.26 CoroutineScope async & launch become instance methods Allows objects to provide scope for coroutines You provide a default context
74. class ShowDetailsViewModel: ViewModel() {• val showRepository: ShowRepository = // ... val state: LiveData<ViewState> private val job = Job() init { refresh() }. private fun refresh() {• launch(parent = job) {• showRepository.updateShow(showId) // update view state }. }. override onCleared() {
75. class ShowDetailsViewModel: ViewModel(), CoroutineScope {• val showRepository: ShowRepository = // ... val state: LiveData<ViewState> private val job = Job() init { refresh() }. private fun refresh() {• launch(parent = job) {• showRepository.updateShow(showId) // update view state }. }. override onCleared() {
76. class ShowDetailsViewModel: ViewModel(), CoroutineScope {• val showRepository: ShowRepository = // ... val state: LiveData<ViewState> private val job = Job() override val coroutineContext: CoroutineContext get() = job + Dispatchers.Main init { refresh() }. private fun refresh() {• launch(parent = job) {• showRepository.updateShow(showId) // update view state }.
77. override val coroutineContext: CoroutineContext get() = job + Dispatchers.Main init { refresh() }. private fun refresh() {• launch(parent = job) {• showRepository.updateShow(showId) // update view state }. }. override onCleared() { super.onCleared() job.cancel() }. }.
78. override val coroutineContext: CoroutineContext get() = job + Dispatchers.Main init { refresh() }. private fun refresh() {• launch {• showRepository.updateShow(showId) // update view state }. }. override onCleared() {• super.onCleared() job.cancel() }. }.
79. override val coroutineContext: CoroutineContext get() = job + Dispatchers.Main init { refresh() }. private fun refresh() {• this.launch(context = coroutineContext) {• showRepository.updateShow(showId) // update view state }. }. override onCleared() {• super.onCleared() job.cancel() }. }.
80. open class ScopedViewModel : ViewModel(), CoroutineScope { private val job = Job() override val coroutineContext: CoroutineContext get() = job + Dispatchers.Main override fun onCleared() { super.onCleared() job.cancel() } }
81. launch { } suspend fun updateShow(showId: Long) {}
 val local = async {}
 localShowStore.getShow(showId)
 }}
 val remote = async {} remoteSource.getShow(showId) }} val merged = mergeShow(local.await(), remote.await()) localShowStore.saveShow(merged) }.
82. launch { } suspend fun updateShow(showId: Long) = coroutineScope {}
 val local = async {}
 localShowStore.getShow(showId)
 }}
 val remote = async {} remoteSource.getShow(showId) }} val merged = mergeShow(local.await(), remote.await()) localShowStore.saveShow(merged) }.
83. launch { } suspend fun updateShow(showId: Long) = coroutineScope {}
 val local = async {}
 localShowStore.getShow(showId)
 }}
 val remote = async {} remoteSource.getShow(showId) }} val merged = mergeShow(local.await(), remote.await()) localShowStore.saveShow(merged) }. Child coroutines Suspended job.cancel() Cancelled Children are cancelled too
84. What if I’m not using ViewModels?
85. open class ScopedFragment : Fragment(), CoroutineScope { private val job = Job() override val coroutineContext: CoroutineContext get() = job + Dispatchers.Main override fun onDestroy() { super.onDestroy() job.cancel() } }
86. // In your Activity / Fragment val observer = MyObserver() getLifecycle().addObserver(observer) class MyObserver : DefaultLifecycleObserver {{ override fun onCreate(owner: LifecycleOwner) {{ // we’re created }- override fun onDestroy(owner: LifecycleOwner) {{ // we’re destroyed }) }{
87. class MyObserver : DefaultLifecycleObserver {{ override fun onCreate(owner: LifecycleOwner) {{ // we’re created }- override fun onDestroy(owner: LifecycleOwner) {{ // we’re destroyed }) }{ // In your Activity / Fragment val observer = MyObserver() getLifecycle().addObserver(observer)
88. class LifecycleScope : DefaultLifecycleObserver {{ override fun onDestroy(owner: LifecycleOwner) {{ // we’re destroyed }) }{
89. class LifecycleScope : DefaultLifecycleObserver {{ val job = Job(){ override fun onDestroy(owner: LifecycleOwner) {{ // we’re destroyed }) }{
90. class LifecycleScope : DefaultLifecycleObserver {{ val job = Job() override fun onDestroy(owner: LifecycleOwner) { // we’re destroyed{ job.cancel() }) }{
91. class LifecycleScope : DefaultLifecycleObserver, CoroutineScope {{ val job = Job() override fun onDestroy(owner: LifecycleOwner) { // we’re destroyed{ job.cancel() }) }{
92. class LifecycleScope : DefaultLifecycleObserver, CoroutineScope {{ val job = Job() override val coroutineContext = job + Dispatchers.Main override fun onDestroy(owner: LifecycleOwner) { // we’re destroyed{ job.cancel() }) }{ class DetailsFragment : Fragment() { private val scope = LifecycleScope() init { lifecycle.addObserver(scope) }}
93. class DetailsFragment : Fragment() { private val scope = LifecycleScope() init { lifecycle.addObserver(scope) }} override fun onCreateView( ...) { // ... }} }} // we’re destroyed{ job.cancel() }) }{
94. class DetailsFragment : Fragment() { private val scope = LifecycleScope() init { lifecycle.addObserver(scope) }} override fun onCreateView( ...) { // ... }} }}
95. class DetailsFragment : Fragment() { private val scope = LifecycleScope() init { lifecycle.addObserver(scope) }} override fun onStart() { scope.launch { // something async } } override fun onCreateView( ...) { // ... }} }}
96. class DetailsFragment : Fragment() { private val scope = LifecycleScope() init { lifecycle.addObserver(scope) }} override fun onStart() { scope.launch { // something async } } override fun onCreateView( ...) { // ... }} }} Scoped to Fragment lifecycle
97. gist.louiscad.com/LifecycleCoroutines
98. Cancellation
99. Cancellation requires co-operation
100. Cancellation requires co-operation Need to check if cancelled
101. Cancellation requires co-operation Need to check if active
102. Call a suspending function Check isActive Two ways to co-operate
103. Call a suspending function Check isActive if (job != null && !job.isActive) { throw job.getCancellationException() } Two ways to co-operate yield()
104. Two ways to co-operate Call a suspending function Check isActive launch { files.forEach { file -> if (isActive) doSomethingWith(file) } }
105. Exceptions
106. launch rethrows exceptions
107. suspend fun updateShow(showId: Long) = coroutineScope {} val local = async {} localShowStore.getShow(showId) }} val remote = async {} remoteSource.getShow(showId) }} val merged = mergeShow(local.await(), remote.await()) localShowStore.saveShow(merged) }}
108. suspend fun updateShow(showId: Long) = coroutineScope {} val local = async {} localShowStore.getShow(showId) }} val trakt = async {} remoteSource.getShow(showId) }} val merged = mergeShow(local.await(), remote.await()) localShowStore.saveShow(merged) // throws CrashyMcCrashfaceException() }}
109. suspend fun updateShow(showId: Long) = coroutineScope {} val local = async {} localShowStore.getShow(showId) }} val trakt = async {} remoteSource.getShow(showId) }} val merged = mergeShow(local.await(), remote.await()) localShowStore.saveShow(merged) // throws CrashyMcCrashfaceException() }} Treated like an uncaught exception
110. async doesn’t throw until await()
111. suspend fun updateShow(showId: Long) = coroutineScope {} val local = async {} localShowStore.getShow(showId) }} val remote = async {} remoteSource.getShow(showId) }} val merged = mergeShow(local.await(), remote.await()) localShowStore.saveShow(merged) }}
112. suspend fun updateShow(showId: Long) = coroutineScope {} val local = async {} localShowStore.getShow(showId) // throws CrashyMcCrashfaceException() }} val remote = async {} remoteSource.getShow(showId) }} val merged = mergeShow(local.await(), remote.await())} localShowStore.saveShow(merged)} }}
113. suspend fun updateShow(showId: Long) = coroutineScope {} val local = async {} localShowStore.getShow(showId) // throws CrashyMcCrashfaceException() }} val remote = async {} remoteSource.getShow(showId) }} val merged = mergeShow(local.await(), remote.await())} localShowStore.saveShow(merged)} }} Thrown here
114. suspend fun updateShow(showId: Long) = coroutineScope {} val local = async {} localShowStore.getShow(showId) // throws CrashyMcCrashfaceException() }} val remote = async {} remoteSource.getShow(showId) }} try {} val merged = mergeShow(local.await(), remote.await()) localShowStore.saveShow(merged) } catch (t: Throwable) {} // Handle the exception }} }}
115. Dispatchers
116. launch {{ // fun things }}
117. launch(context = Dispatchers.Default) {{ // fun things }}
118. What’s a CoroutineDispatcher?
119. What’s a CoroutineDispatcher? The thing which runs and schedules coroutines
120. DefaultScheduler Dispatchers.Default ===
121. DefaultScheduler New! v0.30 Elastic thread executor Uses cpuCount threads (core) Now set as Dispatchers.Default in 0.30
122. New! v0.25 IO Designed for blocking I/O tasks Uses 64 <= cpuCount threads launch(IO) {{ // network things }}
123. IO New! v0.25 Shares threads IO dispatcher uses DefaultScheduler
124. New! v0.25 async { val local = withContext(IO) { fileStore.loadImage( ...) }} // No thread context switch! return processImage(local) }} Shares threads IO dispatcher uses DefaultScheduler IO
125. async { val local = withContext(IO) { fileStore.loadImage( ...) }} // No thread context switch! return processImage(local) }} Shares threads IO dispatcher uses DefaultScheduler New! v0.25 IO
126. async { val local = withContext(IO) { fileStore.loadImage(...) }} // No thread context switch! return processImage(local) }} Shares threads IO dispatcher uses DefaultScheduler New! v0.25 IO
127. ANDROID SUSPENDERS Reactivity
128. Most devs use RxJava for easy threading
129. End up mainly using Single, Maybe & Completable
130. End up mainly using Single, Maybe & Completable Only exist in RxJava RxScala RxGroovy
131. Coroutines can replace Single / Maybe / Completable
132. service.trendingShows() .scheduleOn(schedulers.io) .subscribe(::onTrendingLoaded, ::onError) interface RemoteService {} @GET("/trendingshows") fun trendingShows(): Single<List<Show>> }}
133. val show = withContext(dispatchers.io) {} service.trendingShows().await() }} interface RemoteService {} @GET("/trendingshows") fun trendingShows(): Single<List<Show>> }}
134. val show = withContext(dispatchers.io) {} service.trendingShows().await() }} interface RemoteService {} @GET("/trendingshows") fun trendingShows(): Single<List<Show>> }}
135. interface RemoteService {} @GET("/trendingshows") suspend fun trendingShows(): List<Show> }} val show = withContext(dispatchers.io) {} service.trendingShows().await() }}
136. interface RemoteService {} @GET("/trendingshows") suspend fun trendingShows(): List<Show> }} val show = withContext(dispatchers.io) {} service.trendingShows().await() }} Coming to Retrofit soon™
137. interface RemoteService {} @GET("/trendingshows") suspend fun trendingShows(): List<Show> }} val show = withContext(dispatchers.io) {} service.trendingShows().await() }}
138. interface RemoteService {} @GET("/trendingshows") suspend fun trendingShows(): List<Show> }} val show = withContext(dispatchers.io) {} service.trendingShows() }}
139. Channels
140. Be aware that Channels is experimental Channels
141. Channels Not a replacement for RxJava Publishers Describe an asynchronous stream of things
142. val channel = Channel<Bitmap>() launch { // First coroutine to load images files.forEach { file -> val bitmap = loadBitmap(file) channel.send(bitmap) } // We're done with the channel channel.close() } launch { // Second coroutine to process them
143. val channel = Channel<Bitmap>() launch { // First coroutine to load images files.forEach { file -> val bitmap = loadBitmap(file) channel.send(bitmap) } // We're done with the channel channel.close() } launch { // Second coroutine to process them
144. val channel = Channel<Bitmap>() launch { // First coroutine to load images files.forEach { file -> val bitmap = loadBitmap(file) channel.send(bitmap) } // We're done with the channel channel.close() } launch { // Second coroutine to process them
145. val channel = Channel<Bitmap>() launch { // First coroutine to load images files.forEach { file -> val bitmap = loadBitmap(file) channel.send(bitmap) } // We're done with the channel channel.close() } launch { // Second coroutine to process them
146. files.forEach { file -> val bitmap = loadBitmap(file) channel.send(bitmap) } // We're done with the channel channel.close() } launch { // Second coroutine to process them channel.consumeEach { bitmap -> processBitmap(bitmap) } }
147. BroadcastChannels ≈ Subjects ConflatedBroadcastChannel ≈ BehaviorSubject Channels
148. Channels support null values Channels Channels only support streams "hot"
149. Operators
150. all any associate associateBy associateByTo associateTo consume consumeEach consumeEachIndexed consumes count distinct distinctBy drop dropWhile elementAt elementAtOrElse elementAtOrNull filter filterIndexed filterIndexedTo filterNot filterNotNull filterNotNullTo filterNotTo filterTo find findLast first firstOrNull flatMap fold foldIndexed groupBy groupByTo indexOf indexOfFirst indexOfLast last l a s t I n d e x O f l a s t O r N u l l m a p m a p I n d e x e d mapIndexedNotNull mapIndexedNotNullTo mapIndexedTo mapNotNull mapNotNullTo mapTo maxBy maxWith minBy minWith none partition reduce reduceIndexed requireNoNulls single singleOrNull sumBy sumByDouble take takeWhile toChannel toCollection toList toMap toMutableList toMutableSet toSet withIndex zip Channels has 73 built-in operators
151. aggregate all amb ambWith and apply asObservable asyncAction asyncFunc averageDouble length limit longCount map mapMany materialize max maxBy merge mergeDelayError Compare that to RxJava 230ish
152. Operators are easier to write in coroutines fun <T, R> Publisher<T>.map( context: CoroutineContext, mapper: (T) -> R ) = GlobalScope.publish(context) { consumeEach { send(mapper(it)) } }
153. ANDROID SUSPENDERS Using Android APIs
154. Get last known location One shot callback
155. Get last known location FusedLocationProviderClient In Google Play Services client.getLastLocation(): Task<Location>
156. Get last known location FusedLocationProviderClient client.getLastLocation().addOnCompleteListener { task -> // where am i? val location = task.result } Location In Google Play Services
157. callback ➡ suspend
158. callback ➡ suspend suspendCoroutine { ... }
159. suspendCoroutine { ... } Given a continuation to later resume Will run the lambda and then immediately suspend How you pass the result back
160. Get last known location suspend fun getLastLocation(): Location { }} // TODO
161. Get last known location suspend fun getLastLocation(): Location { return suspendCoroutine { continuation -> }} }} // TODO
162. Get last known location suspend fun getLastLocation(): Location { return suspendCoroutine { continuation -> }} }}
163. Get last known location suspend fun getLastLocation(): Location { return suspendCoroutine { continuation -> locationClient.lastLocation.addOnCompleteListener { task -> continuation.resume(task.result) }} }} }}
164. Get last known location suspend fun getLastLocation(): Location { return suspendCoroutine { continuation -> locationClient.lastLocation.addOnCompleteListener { task -> continuation.resume(task.result) }} }} }} Resumes coroutine with result
165. Get last known location suspend fun getLastLocation(): Location { return suspendCoroutine { continuation -> locationClient.lastLocation.addOnCompleteListener { task -> if (task.isSuccessful) { continuation.resume(task.result) } else { continuation.resumeWithException(task.exception !!) } }} }} }}
166. Observe location updates Multiple value callback
167. FusedLocationProviderClient Takes a callback parameter fun requestLocationUpdates( request: LocationRequest, callback: LocationCallback, looper: Looper ): Task<Void>
168. fun requestLocationUpdates( request: LocationRequest, callback: LocationCallback, looper: Looper ): Task<Void>
169. fun requestLocationUpdates( request: LocationRequest, callback: LocationCallback, looper: Looper ): Task<Void>
170. fun requestLocationUpdates( request: LocationRequest, callback: LocationCallback, looper: Looper ): Task<Void>
171. fun requestLocationUpdates( request: LocationRequest, callback: LocationCallback, looper: Looper ): Task<Void>
172. fun removeLocationUpdates( callback: LocationCallback ): Task<Void> Remove the callback when done request: LocationRequest, callback: LocationCallback, looper: Looper ): Task<Void>
173. fun observeLocation( locationRequest: LocationRequest ): ReceiveChannel<Location> Lets build our function...
174. fun observeLocation( locationRequest: LocationRequest ): ReceiveChannel<Location> {} }}
175. fun observeLocation( locationRequest: LocationRequest ): ReceiveChannel<Location> {} val channel = Channel<Location>() // TODO update channel return channel }}
176. fun observeLocation( locationRequest: LocationRequest ): ReceiveChannel<Location> {} val channel = Channel<Location>() val callback = object : LocationCallback() { override fun onLocationResult(result: LocationResult) { channel.sendBlocking(result.getLastLocation()) }} }} // TODO request location updates return channel }}
177. fun observeLocation( locationRequest: LocationRequest ): ReceiveChannel<Location> { val channel = Channel<Location>() val callback = object : LocationCallback() { override fun onLocationResult(result: LocationResult) { channel.sendBlocking(result.getLastLocation()) } } // TODO request location updates return channel }
178. fun observeLocation( locationRequest: LocationRequest ): ReceiveChannel<Location> { val channel = Channel<Location>() val callback = object : LocationCallback() { override fun onLocationResult(result: LocationResult) { channel.sendBlocking(result.getLastLocation()) }} }} // TODO request location updates return channel }}
179. fun observeLocation( locationRequest: LocationRequest ): ReceiveChannel<Location> { val channel = Channel<Location>() val callback = object : LocationCallback() { override fun onLocationResult(result: LocationResult) { channel.sendBlocking(result.getLastLocation()) }} }} return channel }}
180. fun observeLocation( locationRequest: LocationRequest ): ReceiveChannel<Location> { val channel = Channel<Location>() val callback = object : LocationCallback() { override fun onLocationResult(result: LocationResult) { channel.sendBlocking(result.getLastLocation()) }} }} // Start location updates, sending locations to the // channel locationClient.requestLocationUpdates( locationRequest, callback, Looper.myLooper() )}
181. val channel = Channel<Location>() val callback = object : LocationCallback() { override fun onLocationResult(result: LocationResult) { channel.sendBlocking(result.getLastLocation()) }} }} // Start location updates, sending locations to the // channel locationClient.requestLocationUpdates( locationRequest, callback, Looper.myLooper() )} return channel }}
182. }} // Start location updates, sending locations to the // channel locationClient.requestLocationUpdates( locationRequest, callback, Looper.myLooper() )} // Remove the location callback when the channel // is closed channel.invokeOnClose { locationClient.removeLocationUpdates(callback) } return channel }}
183. lateinit var locationChannel: ReceiveChannel<Location> override fun onStart() { val locationRequest = LocationRequest() .setSmallestDisplacement(100f) // 100m locationChannel = observeLocation(locationRequest) launch(Main) { locationChannel.consumeEach { // We have a new location! updateUiForLocation(it) } } } override fun onStop() { // Stop observing the location and
184. lateinit var locationChannel: ReceiveChannel<Location> override fun onStart() { val locationRequest = LocationRequest() .setSmallestDisplacement(100f) // 100m locationChannel = observeLocation(locationRequest) launch(Main) { locationChannel.consumeEach { // We have a new location! updateUiForLocation(it) } } } override fun onStop() { // Stop observing the location and
185. lateinit var locationChannel: ReceiveChannel<Location> override fun onStart() { val locationRequest = LocationRequest() .setSmallestDisplacement(100f) // 100m locationChannel = observeLocation(locationRequest) launch(Main) { locationChannel.consumeEach { // We have a new location! updateUiForLocation(it) } } } override fun onStop() { // Stop observing the location and
186. lateinit var locationChannel: ReceiveChannel<Location> override fun onStart() { val locationRequest = LocationRequest() .setSmallestDisplacement(100f) // 100m locationChannel = observeLocation(locationRequest) launch(Main) { locationChannel.consumeEach { // We have a new location! updateUiForLocation(it) }} }} }} override fun onStop() { // Stop observing the location and
187. .setSmallestDisplacement(100f) // 100m locationChannel = observeLocation(locationRequest) launch(Main) { locationChannel.consumeEach { // We have a new location! updateUiForLocation(it) }} }} }} override fun onStop() { // Stop observing the location and // close the channel locationChannel.cancel() }}
188. .setSmallestDisplacement(100f) // 100m locationChannel = observeLocation(locationRequest) launch(Main) { locationChannel.consumeEach { // We have a new location! updateUiForLocation(it) }} }} }} override fun onStop() { // Stop observing the location and // close the channel locationChannel.cancel() }}
189. ANDROID SUSPENDERS What's next?
190. Codelab https:/ /codelabs.developers.google.com/codelabs/kotlin-coroutines/
191. RTFM
192. Exploring Coroutines in Kotlin Kotlin Coroutines in Practice Coroutines and Reactive Programming - friends or foes? Effectenbeurzaal Tomorrow, 13:00 Effectenbeurzaal Tomorrow, 10:15 Granbeurszaal Tomorrow, 15:15
193. Over and out… @chrisbanes