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
   

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2. ANDROID SUSPENDERS
   chris.banes.me/suspenders
   

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3. Android’s main thread
   

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4. Android’s main thread
   measure + layout
   draw
   View inflation
   and many more things
   

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5. ms
   60Hz
   16
   Android’s main thread
   

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6. 12 ms
   Android’s main thread
   90Hz
   

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7. ms
   120Hz
   8
   Android’s main thread
   

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9. ASYNC ALL THE THINGS
   

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10. How do we do that?
    

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11. Executors
    AsyncTask
    How do we do that?
    

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12. Loaders
    Executors
    AsyncTask
    How do we do that?
    

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13. Future
    Executors
    Loaders
    How do we do that?
    

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14. Libraries
    Loaders
    Future
    How do we do that?
    

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15. WorkManager
    Future
    Libraries
    How do we do that?
    

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16. Coroutines
    Libraries
    Coroutines
    How do we do that?
    

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17. Coroutines
    Libraries
    Coroutines
    So why use
    ?
    

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18. What does your typical
    mobile app do?
    

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19. CRUD
    What does your typical
    mobile app do?
    

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20. C R U D
    reate ead pdate elete
    What does your typical
    mobile app do?
    

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21. Sync
    What does your typical
    mobile app do?
    

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22. Sync
    What does your typical
    mobile app do?
    

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23. So why coroutines?
    Scale on limited hardware
    Easier development model
    Great for I/O tasks
    

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24. Tivi
    github.com/chrisbanes/tivi
    

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25. kotlinx-coroutines-core
    -android
    -rx2
    

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26. -core
    -android
    -rx2
    jars: 774KB
    

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27. -core
    -android
    -rx2
    jars: 774KB
    apk: 499KB
    3260 method refs
    

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28. -core
    -android
    -rx2
    jars: 774KB
    apk: 499KB
    3260 method refs
    r8: 113KB
    1208 method refs
    

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29. -core
    -android
    -rx2
    jars: 774KB
    apk: 499KB
    3260 method refs
    r8: 113KB
    1208 method refs
    r8

    optimized:
    99KB
    834 method refs
    

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30. -keepclassmembernames class kotlinx.** {
    volatile ;
    }
    

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31. ANDROID SUSPENDERS
    Creating routines
    

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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)
    }.
    

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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
    

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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
    

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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
    

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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)
    }.
    

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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
    

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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)
    }.
    

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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)
    }.
    

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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)
    }.
    

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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)
    }.
    

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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)
    }.
    

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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
    

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44. How do we use them
    on Android?
    

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45. class ShowDetailsViewModel: ViewModel() {
    val showRepository: ShowRepository = // ...
    val state: LiveData
    init {
    refresh()
    }
    private fun refresh() {
    launch {
    showRepository.updateShow(showId)
    // update view state
    }
    }
    }
    

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46. class ShowDetailsViewModel: ViewModel() {
    val showRepository: ShowRepository = // ...
    val state: LiveData
    init {
    refresh()
    }
    private fun refresh() {
    launch {
    showRepository.updateShow(showId)
    // update view state
    }
    }
    }
    

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47. class ShowDetailsViewModel: ViewModel() {
    val showRepository: ShowRepository = // ...
    val state: LiveData
    init {
    refresh()
    }
    private fun refresh() {
    launch {
    showRepository.updateShow(showId)
    // update view state
    }
    }
    }
    

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48. class ShowDetailsViewModel: ViewModel() {
    val showRepository: ShowRepository = // ...
    val state: LiveData
    init {
    refresh()
    }
    private fun refresh() {
    launch {
    showRepository.updateShow(showId)
    // update view state
    }
    }
    }
    

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49. class ShowDetailsViewModel: ViewModel() {
    val showRepository: ShowRepository = // ...
    val state: LiveData
    init {•
    refresh()
    }.
    private fun refresh() {•
    launch {•
    showRepository.updateShow(showId)
    // update view state
    }.
    }.
    }.
    

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50. Jobs
    

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51. class ShowDetailsViewModel: ViewModel() {
    private fun refresh() {
    launch {
    showRepository.updateShow(showId)
    // update view state
    }.
    }.
    }.
    

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52. class ShowDetailsViewModel: ViewModel() {
    private fun refresh() {
    val job = launch {
    showRepository.updateShow(showId)
    // update view state
    }.
    }.
    }.
    

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53. class ShowDetailsViewModel: ViewModel() {
    private fun refresh() {
    val job = launch {
    showRepository.updateShow(showId)
    // update view state
    }.
    // can call job.cancel()
    }.
    }.
    

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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()
    }.
    }.
    

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55. class ShowDetailsViewModel: ViewModel() {
    private var updateShowJob: Job? = null
    private fun refresh() {
    updateShowJob = launch {
    showRepository.updateShow(showId)
    // update view state
    }.
    // can call job.cancel()
    }.
    }.
    

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56. class ShowDetailsViewModel: ViewModel() {
    private var updateShowJob: Job? = null
    private fun refresh() {
    updateShowJob = launch {
    showRepository.updateShow(showId)
    // update view state
    }.
    }.
    }.
    

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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()
    }
    }.
    

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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()
    }
    }.
    

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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()
    }
    }.
    

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60. Coroutines can have a
    parent-child relationship
    

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61. Coroutines can have a
    parent-child relationship
    Expressed via Jobs
    (in a context)
    

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62. class ShowDetailsViewModel: ViewModel() {
    val showRepository: ShowRepository = // ...
    val state: LiveData
    private val job = Job()
    init {•
    refresh()
    }.
    private fun refresh() {•
    launch(parent = job) {•
    showRepository.updateShow(showId)
    // update view state
    }.
    }.
    

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63. class ShowDetailsViewModel: ViewModel() {
    val showRepository: ShowRepository = // ...
    val state: LiveData
    private val job = Job()
    init {
    refresh()
    }.
    private fun refresh() {
    launch(parent = job) {
    showRepository.updateShow(showId)
    // update view state
    }.
    }.
    override onCleared() {
    

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64. private val job = Job()
    init {
    refresh()
    }.
    private fun refresh() {
    launch(parent = job) {
    showRepository.updateShow(showId)
    // update view state
    }.
    }.
    override onCleared() {
    job.cancel()
    } ..
    }.
    

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65. private val job = Job()
    init {
    refresh()
    }.
    private fun refresh() {
    launch(parent = job) {
    showRepository.updateShow(showId)
    // update view state
    }.
    }.
    override onCleared() {
    job.cancel()
    }
    } ..
    

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66. private val job = Job()
    init {
    refresh()
    }.
    private fun refresh() {
    launch(parent = job) {
    showRepository.updateShow(showId)
    // update view state
    }.
    }.
    override onCleared() {
    job.cancel()
    }
    } ..
    

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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
    

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68. Scopes
    

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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
    

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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)
    }.
    

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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
    

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72. init {
    refresh()
    }.
    private fun refresh() {
    launch(parent = job) {
    showRepository.updateShow(showId)
    // update view state
    }.
    }.
    override onCleared() {
    Deprecated in v0.26
    async too
    

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73. New!
    v0.26
    CoroutineScope
    async & launch become instance methods
    Allows objects to provide scope for coroutines
    You provide a default context
    

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74. class ShowDetailsViewModel: ViewModel() {•
    val showRepository: ShowRepository = // ...
    val state: LiveData
    private val job = Job()
    init {
    refresh()
    }.
    private fun refresh() {•
    launch(parent = job) {•
    showRepository.updateShow(showId)
    // update view state
    }.
    }.
    override onCleared() {
    

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75. class ShowDetailsViewModel: ViewModel(), CoroutineScope {•
    val showRepository: ShowRepository = // ...
    val state: LiveData
    private val job = Job()
    init {
    refresh()
    }.
    private fun refresh() {•
    launch(parent = job) {•
    showRepository.updateShow(showId)
    // update view state
    }.
    }.
    override onCleared() {
    

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76. class ShowDetailsViewModel: ViewModel(), CoroutineScope {•
    val showRepository: ShowRepository = // ...
    val state: LiveData
    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
    }.
    

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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()
    }.
    }.
    

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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()
    }.
    }.
    

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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()
    }.
    }.
    

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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()
    }
    }
    

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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)
    }.
    

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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)
    }.
    

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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
    

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84. What if I’m not using
    ViewModels?
    

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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()
    }
    }
    

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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
    })
    }{
    

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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)
    

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88. class LifecycleScope : DefaultLifecycleObserver {{
    override fun onDestroy(owner: LifecycleOwner) {{
    // we’re destroyed
    })
    }{
    

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89. class LifecycleScope : DefaultLifecycleObserver {{
    val job = Job(){
    override fun onDestroy(owner: LifecycleOwner) {{
    // we’re destroyed
    })
    }{
    

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90. class LifecycleScope : DefaultLifecycleObserver {{
    val job = Job()
    override fun onDestroy(owner: LifecycleOwner) {
    // we’re destroyed{
    job.cancel()
    })
    }{
    

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91. class LifecycleScope : DefaultLifecycleObserver, CoroutineScope {{
    val job = Job()
    override fun onDestroy(owner: LifecycleOwner) {
    // we’re destroyed{
    job.cancel()
    })
    }{
    

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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)
    }}
    

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93. class DetailsFragment : Fragment() {
    private val scope = LifecycleScope()
    init {
    lifecycle.addObserver(scope)
    }}
    override fun onCreateView( ...) {
    // ...
    }}
    }}
    // we’re destroyed{
    job.cancel()
    })
    }{
    

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94. class DetailsFragment : Fragment() {
    private val scope = LifecycleScope()
    init {
    lifecycle.addObserver(scope)
    }}
    override fun onCreateView( ...) {
    // ...
    }}
    }}
    

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95. class DetailsFragment : Fragment() {
    private val scope = LifecycleScope()
    init {
    lifecycle.addObserver(scope)
    }}
    override fun onStart() {
    scope.launch {
    // something async
    }
    }
    override fun onCreateView( ...) {
    // ...
    }}
    }}
    

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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
    

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97. gist.louiscad.com/LifecycleCoroutines
    

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98. Cancellation
    

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99. Cancellation
    requires co-operation
    

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100. Cancellation
     requires co-operation
     Need to check if cancelled
     

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101. Cancellation
     requires co-operation
     Need to check if active
     

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102. Call a suspending function
     Check isActive
     Two ways to co-operate
     

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103. Call a suspending function
     Check isActive
     if (job != null && !job.isActive) {
     throw job.getCancellationException()
     }
     Two ways to co-operate
     yield()
     

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104. Two ways to co-operate
     Call a suspending function
     Check isActive
     launch {
     files.forEach { file ->
     if (isActive) doSomethingWith(file)
     }
     }
     

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105. Exceptions
     

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106. launch rethrows
     exceptions
     

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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)
     }}
     

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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()
     }}
     

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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
     

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110. async doesn’t throw
     until await()
     

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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)
     }}
     

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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)}
     }}
     

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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
     

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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
     }}
     }}
     

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115. Dispatchers
     

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116. launch {{
     // fun things
     }}
     

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117. launch(context = Dispatchers.Default) {{
     // fun things
     }}
     

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118. What’s a
     CoroutineDispatcher?
     

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119. What’s a
     CoroutineDispatcher?
     The thing which runs and
     schedules coroutines
     

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120. DefaultScheduler
     Dispatchers.Default
     ===
     

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121. DefaultScheduler
     New!
     v0.30
     Elastic thread executor
     Uses cpuCount threads (core)
     Now set as Dispatchers.Default in 0.30
     

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122. New!
     v0.25
     IO
     Designed for blocking I/O tasks
     Uses 64 <= cpuCount threads
     launch(IO) {{
     // network things
     }}
     

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123. IO
     New!
     v0.25
     Shares threads
     IO dispatcher uses DefaultScheduler
     

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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
     

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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
     

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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
     

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127. ANDROID SUSPENDERS
     Reactivity
     

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128. Most devs use RxJava
     for easy threading
     

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129. End up mainly using Single,
     Maybe & Completable
     

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130. End up mainly using Single,
     Maybe & Completable
     Only exist in RxJava
     RxScala
     RxGroovy
     

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131. Coroutines
     can replace
     Single / Maybe / Completable
     

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132. service.trendingShows()
     .scheduleOn(schedulers.io)
     .subscribe(::onTrendingLoaded, ::onError)
     interface RemoteService {}
     @GET("/trendingshows")
     fun trendingShows(): Single>
     }}
     

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133. val show = withContext(dispatchers.io) {}
     service.trendingShows().await()
     }}
     interface RemoteService {}
     @GET("/trendingshows")
     fun trendingShows(): Single>
     }}
     

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134. val show = withContext(dispatchers.io) {}
     service.trendingShows().await()
     }}
     interface RemoteService {}
     @GET("/trendingshows")
     fun trendingShows(): Single>
     }}
     

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135. interface RemoteService {}
     @GET("/trendingshows")
     suspend fun trendingShows(): List
     }}
     val show = withContext(dispatchers.io) {}
     service.trendingShows().await()
     }}
     

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136. interface RemoteService {}
     @GET("/trendingshows")
     suspend fun trendingShows(): List
     }}
     val show = withContext(dispatchers.io) {}
     service.trendingShows().await()
     }}
     Coming to Retrofit soon™
     

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137. interface RemoteService {}
     @GET("/trendingshows")
     suspend fun trendingShows(): List
     }}
     val show = withContext(dispatchers.io) {}
     service.trendingShows().await()
     }}
     

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138. interface RemoteService {}
     @GET("/trendingshows")
     suspend fun trendingShows(): List
     }}
     val show = withContext(dispatchers.io) {}
     service.trendingShows()
     }}
     

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139. Channels
     

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140. Be aware that Channels
     is experimental
     Channels
     

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141. Channels
     Not a replacement for RxJava Publishers
     Describe an asynchronous stream of things
     

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142. val channel = Channel()
     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
     

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143. val channel = Channel()
     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
     

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144. val channel = Channel()
     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
     

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145. val channel = Channel()
     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
     

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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)
     }
     }
     

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147. BroadcastChannels ≈ Subjects
     ConflatedBroadcastChannel ≈ BehaviorSubject
     Channels
     

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148. Channels support null values
     Channels
     Channels only support streams
     "hot"
     

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149. Operators
     

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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
     

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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
     

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152. Operators are easier to write in
     coroutines
     fun Publisher.map(
     context: CoroutineContext,
     mapper: (T) -> R
     ) = GlobalScope.publish(context) {
     consumeEach {
     send(mapper(it))
     }
     }
     

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153. ANDROID SUSPENDERS
     Using Android APIs
     

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154. Get last known location
     One shot callback
     

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155. Get last known location
     FusedLocationProviderClient
     In Google Play Services
     client.getLastLocation(): Task
     

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156. Get last known location
     FusedLocationProviderClient
     client.getLastLocation().addOnCompleteListener { task ->
     // where am i?
     val location = task.result
     }
     Location
     In Google Play Services
     

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157. callback ➡ suspend
     

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158. callback ➡ suspend
     suspendCoroutine { ... }
     

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159. suspendCoroutine { ... }
     Given a continuation to later resume
     Will run the lambda and then immediately suspend
     How you pass the result back
     

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160. Get last known location
     suspend fun getLastLocation(): Location {
     }}
     // TODO
     

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161. Get last known location
     suspend fun getLastLocation(): Location {
     return suspendCoroutine { continuation ->
     }}
     }}
     // TODO
     

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162. Get last known location
     suspend fun getLastLocation(): Location {
     return suspendCoroutine { continuation ->
     }}
     }}
     

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163. Get last known location
     suspend fun getLastLocation(): Location {
     return suspendCoroutine { continuation ->
     locationClient.lastLocation.addOnCompleteListener { task ->
     continuation.resume(task.result)
     }}
     }}
     }}
     

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164. Get last known location
     suspend fun getLastLocation(): Location {
     return suspendCoroutine { continuation ->
     locationClient.lastLocation.addOnCompleteListener { task ->
     continuation.resume(task.result)
     }}
     }}
     }}
     Resumes coroutine
     with result
     

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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 !!)
     }
     }}
     }}
     }}
     

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166. Observe location updates
     Multiple value callback
     

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167. FusedLocationProviderClient
     Takes a callback parameter
     fun requestLocationUpdates(
     request: LocationRequest,
     callback: LocationCallback,
     looper: Looper
     ): Task
     

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168. fun requestLocationUpdates(
     request: LocationRequest,
     callback: LocationCallback,
     looper: Looper
     ): Task
     

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169. fun requestLocationUpdates(
     request: LocationRequest,
     callback: LocationCallback,
     looper: Looper
     ): Task
     

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170. fun requestLocationUpdates(
     request: LocationRequest,
     callback: LocationCallback,
     looper: Looper
     ): Task
     

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171. fun requestLocationUpdates(
     request: LocationRequest,
     callback: LocationCallback,
     looper: Looper
     ): Task
     

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172. fun removeLocationUpdates(
     callback: LocationCallback
     ): Task
     Remove the callback
     when done
     request: LocationRequest,
     callback: LocationCallback,
     looper: Looper
     ): Task
     

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173. fun observeLocation(
     locationRequest: LocationRequest
     ): ReceiveChannel
     Lets build our function...
     

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174. fun observeLocation(
     locationRequest: LocationRequest
     ): ReceiveChannel {}
     }}
     

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175. fun observeLocation(
     locationRequest: LocationRequest
     ): ReceiveChannel {}
     val channel = Channel()
     // TODO update channel
     return channel
     }}
     

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176. fun observeLocation(
     locationRequest: LocationRequest
     ): ReceiveChannel {}
     val channel = Channel()
     val callback = object : LocationCallback() {
     override fun onLocationResult(result: LocationResult) {
     channel.sendBlocking(result.getLastLocation())
     }}
     }}
     // TODO request location updates
     return channel
     }}
     

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177. fun observeLocation(
     locationRequest: LocationRequest
     ): ReceiveChannel {
     val channel = Channel()
     val callback = object : LocationCallback() {
     override fun onLocationResult(result: LocationResult) {
     channel.sendBlocking(result.getLastLocation())
     }
     }
     // TODO request location updates
     return channel
     }
     

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178. fun observeLocation(
     locationRequest: LocationRequest
     ): ReceiveChannel {
     val channel = Channel()
     val callback = object : LocationCallback() {
     override fun onLocationResult(result: LocationResult) {
     channel.sendBlocking(result.getLastLocation())
     }}
     }}
     // TODO request location updates
     return channel
     }}
     

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179. fun observeLocation(
     locationRequest: LocationRequest
     ): ReceiveChannel {
     val channel = Channel()
     val callback = object : LocationCallback() {
     override fun onLocationResult(result: LocationResult) {
     channel.sendBlocking(result.getLastLocation())
     }}
     }}
     return channel
     }}
     

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180. fun observeLocation(
     locationRequest: LocationRequest
     ): ReceiveChannel {
     val channel = Channel()
     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()
     )}
     

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181. val channel = Channel()
     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
     }}
     

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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
     }}
     

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183. lateinit var locationChannel: ReceiveChannel
     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
     

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184. lateinit var locationChannel: ReceiveChannel
     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
     

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185. lateinit var locationChannel: ReceiveChannel
     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
     

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186. lateinit var locationChannel: ReceiveChannel
     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
     

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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()
     }}
     

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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()
     }}
     

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189. ANDROID SUSPENDERS
     What's next?
     

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190. Codelab
     https:/
     /codelabs.developers.google.com/codelabs/kotlin-coroutines/
     

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191. RTFM
     

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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
     

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193. Over and out…
     @chrisbanes
     

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