Coroutines and Rx: A battle towards Asynchrony

This was given at Droidcon SF 2019

Transcript

1. Coroutines and Rx: A Battle Towards
   Asynchrony
   @droid_singh
   ⚔
   

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2. Reactive Extensions
   “Push Based Updates”
   

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3. showsApi.getShowByName("Friends")
   .flatmap { showsApi.getCharacters(it.id) }
   .subscribe(
   { /* do something with characters*/ },
   { /* handle errors retrieving characters*/}
   )
   

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4. showsApi.getShowByName("Friends")
   .flatmap { showsApi.getCharacters(it.id) }
   .subscribe(
   { /* do something with characters*/ },
   { /* handle errors retrieving characters*/}
   )
   

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5. showsApi.getShowByName("Friends")
   .flatmap { showsApi.getCharacters(it.id) }
   .subscribe(
   { /* do something with characters*/ },
   { /* handle errors retrieving characters*/}
   )
   -Ben Christensen
   

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6. Coroutines
   “Non blocking subroutines”
   

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7. CoroutineScope.launch(Dispatchers.IO){
   val show = showsApi.getShowByName("Friends")
   val characters = showsApi.getCharacters(show.id)
   withContext(Dispatchers.Main){
   // do something with characters on UI
   }
   }
   

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8. I
   O
   CoroutineScope.launch(Dispatchers.IO){
   val show = showsApi.getShowByName("Friends")
   val characters = showsApi.getCharacters(show.id)
   withContext(Dispatchers.Main){
   // do something with characters on UI
   }
   }
   

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9. I
   O
   0
   sm.item = "Friends"
   sm.label = 1
   CoroutineScope.launch(Dispatchers.IO){
   val show = showsApi.getShowByName("Friends")
   val characters = showsApi.getCharacters(show.id)
   withContext(Dispatchers.Main){
   // do something with characters on UI
   }
   }
   

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10. I
    O
    0
    sm.item = "Friends"
    sm.label = 1
    showsApi.getShowsByName(“Friends”, cont)
    Continuation
    CoroutineScope.launch(Dispatchers.IO){
    val show = showsApi.getShowByName("Friends")
    val characters = showsApi.getCharacters(show.id)
    withContext(Dispatchers.Main){
    // do something with characters on UI
    }
    }
    

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11. I
    O
    0 1
    show = sm.result
    sm.label = 2
    sm.item = "Friends"
    sm.label = 1
    showsApi.getShowsByName(“Friends”, cont)
    CoroutineScope.launch(Dispatchers.IO){
    val show = showsApi.getShowByName("Friends")
    val characters = showsApi.getCharacters(show.id)
    withContext(Dispatchers.Main){
    // do something with characters on UI
    }
    }
    

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12. I
    O
    0 1
    show = sm.result
    sm.label = 2
    showsApi.getCharacters(show.id, cont)
    sm.item = "Friends"
    sm.label = 1
    showsApi.getShowsByName(“Friends”, cont)
    Continuation
    CoroutineScope.launch(Dispatchers.IO){
    val show = showsApi.getShowByName("Friends")
    val characters = showsApi.getCharacters(show.id)
    withContext(Dispatchers.Main){
    // do something with characters on UI
    }
    }
    

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13. I
    O
    0 1
    show = sm.result
    sm.label = 2
    showsApi.getCharacters(show.id, cont)
    sm.item = "Friends"
    sm.label = 1
    showsApi.getShowsByName(“Friends”, cont)
    Continuation
    2
    characters = sm.result
    CoroutineScope.launch(Dispatchers.IO){
    val show = showsApi.getShowByName("Friends")
    val characters = showsApi.getCharacters(show.id)
    withContext(Dispatchers.Main){
    // do something with characters on UI
    }
    }
    

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14. ⚔
    ASYNCHRONICITY
    

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15. ! ! !
    “Do not walk away from complexity, Run”
    - Venkat Subramaniam
    

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16. Round 1:
    The Initial Combat
    ⚔
    

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17. HTTP over
    Retrofit.Builder()
    .baseUrl(MoviesApiInterface.MOVIES_ENDPOINT)
    .addConverterFactory(gsonConverterFactory)
    .addCallAdapterFactory(rxJavaCallAdapterFactory)
    .client(okHttp)
    .build()
    .create(MoviesApiInterface::class.java)
    

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18. moviesApi.getLatestMovies( )
    .subscribeOn(Schedulers.io())
    .observeOn(AndroidSchedulers.mainThread())
    .subscribe(
    { /* do something with movies*/ },
    { /* handle errors retrieving movies*/}
    )
    HTTP over
    

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19. Retrofit.Builder()
    .baseUrl(MoviesApiInterface.MOVIES_ENDPOINT)
    .addConverterFactory(gsonConverterFactory)
    .client(okHttp)
    .build()
    .create(MoviesApiInterface::class.java)
    HTTP over
    

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20. No Change
    HTTP over
    Retrofit.Builder()
    .baseUrl(MoviesApiInterface.MOVIES_ENDPOINT)
    .addConverterFactory(gsonConverterFactory)
    .client(okHttp)
    .build()
    .create(MoviesApiInterface::class.java)
    

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21. CoroutineScope.launch{
    val data = moviesApiInterface.getInTheatreMovies()
    withContext(Dispatchers.Main){
    // do something with data
    }
    }
    HTTP over
    

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22. Operators
    Learning
    
    

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23. Operators
    Learning
    
    

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24. ~11k ~3k
    https://github.com/KeepSafe/dexcount-gradle-plugin
    

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25. Complexity
    Most
    Most
    

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26. Round 2:
    Let’s catch that
    ⚔
    

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27. Error Propagation over
    1 2 3 5
    N N / N - 4
    4
    

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28. Error Propagation over
    1 2 3 5
    N N / N - 4
    -1/3 -1 -3
    Destructive
    4
    

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29. Error Handling
    • Wrap your response in Result class
    sealed class Result {
    data class Success(val data: T) : Result()
    data class Error(val exception: Exception) : Result()
    }
    • Gotta catch them all
    onError
    onErrorReturn onErrorResumeNext
    doOnError onErrorComplete
    onErrorReturnItem
    

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30. Error Handling
    fun getMovies(): Observable> {
    return moviesApi.getMovies()
    .map { Result.Success(it) }
    .onErrorReturn { Result.Error(it) }
    }
    

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31. Error Handling
    fun getMovies(): Observable> {
    return moviesApi.getMovies()
    .map { Result.Success(it) }
    .onErrorReturn { Result.Error(it) }
    }
    Result
    
    

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32. Error Propagation over
    

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33. Error Propagation over
    Parent-Child Relationship
    

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34. Error Propagation over
    Parent-Child Relationship
    Exceptions

    Bubbling

    Tendency
    

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35. Error Propagation over
    

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36. “Exceptions are like virus for Coroutines”
    Error Propagation over
    

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37. Error Handling over
    • Depends on what Coroutine Builder you are using: Launch/Async?
    • Scope Intelligently
    
    • Tools for handling
    ☠
    CoroutineExceptionHandler
    try/catch
    

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38. Error Handling over
    private val context: CoroutineContext = Job() + Dispatchers.IO
    val scope = CoroutineScope(context)
    suspend fun longRunningTask(): Unit {
    delay(100)
    throw IllegalArgumentException()
    }
    • Setup
    

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39. Error Handling over
    • launch CoroutineBuilder
    scope.launch{
    launch{
    longRunningTask()
    }
    }
    

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40. Error Handling over
    • Install CoroutineExceptionHandler
    private val ceh = CoroutineExceptionHandler { _, e ->
    println("CEH Handled Crash [$e]")
    } scope.launch(ceh){
    launch{
    longRunningTask()
    }
    }
    

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41. Error Handling over
    • Async CoroutineBuilder
    scope.launch{
    async{
    longRunningTask()
    }.await()
    }
    

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42. Error Handling over
    • Install try/catch
    scope.launch(ceh){
    try{
    async{
    longRunningTask()
    }.await()
    } catch(e: Throwable){
    println("Caught")
    }
    }
    

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43. suspend fun apiCall(call: suspend () -> Result,
    errorMessage: String): Result {
    return try {
    call()
    } catch (e: Exception) {
    Result.Error(e)
    }
    }
    Let’s be a pro
    

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44. suspend fun apiCall(call: suspend () -> Result,
    errorMessage: String): Result {
    return try {
    call()
    } catch (e: Exception) {
    Result.Error(e)
    }
    }
    Result
    Let’s be a pro
    

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45. suspend fun getLatestMovies(): Result {
    return apiCall(
    {
    val data = moviesApiInterface.getInTheatreMovies()
    return@apiCall Result.Success(data.body())
    },
    "Couldn't get"
    )
    }
    So, Now are we pro?
    Let’s be a pro
    

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46. 
    No
    Let’s be a pro
    So, Now are we pro?
    suspend fun getLatestMovies(): Result {
    return apiCall(
    {
    val data = moviesApiInterface.getInTheatreMovies()
    return@apiCall Result.Success(data.body())
    },
    "Couldn't get"
    )
    }
    

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47. Complexity
    Most
    Most
    

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48. Round 3:
    Let’s zip them
    ⚔
    

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49. Zip Calls in
    Observable.zip(getPopularMovies(), getNowPlayingMovies(),
    BiFunction { popularMovies, topRatedMovies, ->
    // Filter from popular and top rated movies
    }.subscribeOn(Scheduler.io())
    

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50. Zip Calls in
    Let’s apply TEST rule
    Observable.zip(getPopularMovies(), getNowPlayingMovies(),
    BiFunction { popularMovies, topRatedMovies, ->
    // Filter from popular and top rated movies
    }.subscribeOn(Scheduler.io())
    

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51. Zip Calls in
    Threading
    Exception Handling
    Scalability
    Transforming results
    Observable.zip(getPopularMovies(), getNowPlayingMovies(),
    BiFunction { popularMovies, topRatedMovies, ->
    // Filter from popular and top rated movies
    }.subscribeOn(Scheduler.io())
    

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52. Zip Calls in
    Threading
    Exception Handling
    Scalability
    Transforming results
    Observable.zip(getPopularMovies(), getNowPlayingMovies(),
    BiFunction { popularMovies, topRatedMovies, ->
    // Filter from popular and top rated movies
    }.subscribeOn(Scheduler.io())
    

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53. Zip Calls in
    Threading
    Exception Handling
    Scalability
    Transforming results
    Observable.zip(getPopularMovies(), getNowPlayingMovies(),
    BiFunction { popularMovies, topRatedMovies, ->
    // Filter from popular and top rated movies
    }.subscribeOn(Scheduler.io())
    

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54. Zip Calls in
    Threading
    Exception Handling
    Scalability
    Transforming results
    Observable.zip(getPopularMovies(), getNowPlayingMovies(),
    BiFunction { popularMovies, topRatedMovies, ->
    // Filter from popular and top rated movies
    }.subscribeOn(Scheduler.io())
    

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55. Zip Calls in
    • Let’s cook zip
    +
    

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56. suspend fun zip(source1: Deferred, source2: Deferred,
    zipper: (T1, T2) -> R) = coroutineScope {
    // wait for two calls to complete
    async { zipper(source1.await(), source2.await()) }
    }
    Zip Calls in
    • Let’s cook zip
    +
    

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57. suspend fun zip(source1: Deferred, source2: Deferred,
    zipper: (T1, T2) -> R) = coroutineScope {
    // wait for two calls to complete
    async { zipper(source1.await(), source2.await()) }
    }
    Zip Calls in
    • Let’s cook zip
    + Zip
    Deferred 1
    Deferred 2
    Zipper
    Result
    

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58. suspend fun zip(source1: Deferred, source2: Deferred,
    zipper: (T1, T2) -> R) = coroutineScope {
    // wait for two calls to complete
    async { zipper(source1.await(), source2.await()) }
    }
    Zip Calls in
    • Let’s cook zip
    +
    

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59. Zip Calls in
    coroutineScope.launch {
    val popularMovies = async{ getPopularMovies() }
    val topRatedMovies = async{ getTopRatedMovies() }
    zip(popularMovies, topRatedMovies) { popularResults, topRatedResults ->
    // Filter from popular and top rated movies
    return filteredResults
    }.await()
    }
    Threading
    Exception Handling
    Scalability
    Transforming results
    

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60. Threading
    Exception Handling
    Scalability
    Transforming results
    coroutineScope.launch {
    val popularMovies = async{ getPopularMovies() }
    val topRatedMovies = async{ getTopRatedMovies() }
    zip(popularMovies, topRatedMovies) { popularResults, topRatedResults ->
    // Filter from popular and top rated movies
    return filteredResults
    }.await()
    }
    Zip Calls in
    

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61. Threading
    Exception Handling
    Scalability
    Transforming results
    coroutineScope.launch {
    val popularMovies = async{ getPopularMovies() }
    val topRatedMovies = async{ getTopRatedMovies() }
    zip(popularMovies, topRatedMovies) { popularResults, topRatedResults ->
    // Filter from popular and top rated movies
    return filteredResults
    }.await()
    }
    Zip Calls in
    

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62. Threading
    Exception Handling
    Scalability
    Transforming results
    coroutineScope.launch {
    val popularMovies = async{ getPopularMovies() }
    val topRatedMovies = async{ getTopRatedMovies() }
    zip(popularMovies, topRatedMovies) { popularResults, topRatedResults ->
    // Filter from popular and top rated movies
    return filteredResults
    }.await()
    }
    Zip Calls in
    

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63. Complexity
    Most
    Most
    

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64. Round 4:
    Managing States
    ⚔
    

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65. https://jakewharton.com/the-state-of-managing-state-with-rxjava/
    

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66. val events = searchButton.clicks()
    .map { SearchEvent(searchEditText.text.toString()) }
    Power of RxBindings
    State Management through
    

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67. State Management through
    Rich with operators, Adheres to R&FP, exceptional handling, 

    lifecycle management, etc.
    val models = events.flatMap { moviesClient.searchMovies(it.searchTerm) }
    .map { it.results.asResult() }
    .onErrorReturn { Result.Error(it.toApplicationError()) }
    .subscribeOn(Schedulers.io())
    .observeOn(AndroidSchedulers.mainThread())
    

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68. Rich with operators, Adheres to R&FP, exceptional handling, 

    lifecycle management, etc.
    val models = events.flatMap { moviesClient.searchMovies(it.searchTerm) }
    .map { it.results.asResult() }
    .onErrorReturn { Result.Error(it.toApplicationError()) }
    .subscribeOn(Schedulers.io())
    .observeOn(AndroidSchedulers.mainThread())
    State Management through
    

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69. Rich with operators, Adheres to R&FP, exceptional handling, 

    lifecycle management, etc.
    val models = events.flatMap { moviesClient.searchMovies(it.searchTerm) }
    .map { it.results.asResult() }
    .onErrorReturn { Result.Error(it.toApplicationError()) }
    .subscribeOn(Schedulers.io())
    .observeOn(AndroidSchedulers.mainThread())
    State Management through
    

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70. Rich with operators, Adheres to R&FP, exceptional handling, 

    lifecycle management, etc.
    val models = events.flatMap { moviesClient.searchMovies(it.searchTerm) }
    .map { it.results.asResult() }
    .onErrorReturn { Result.Error(it.toApplicationError()) }
    .subscribeOn(Schedulers.io())
    .observeOn(AndroidSchedulers.mainThread())
    State Management through
    

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71. What about Coroutines?
    
    

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72. What about Coroutines?
    
    Flows
    

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73. • Suspension based reactive streams.
    • Can be used to represent streams
    State Management through
    

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74. • Suspension based reactive streams.
    • Can be used to represent streams
    State Management through
    

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75. • Rich with operators, Adheres to R&FP, exceptional handling, 

    lifecycle management, etc.
    viewModelScope.launch {
    flowOf(moviesClient.searchMoviesAsync(query).await())
    .map { Result.Success(it.results) }
    .catch {
    Result.Error(it.toApplicationError())
    }.collect {
    searchStates.postValue(it)
    }
    }
    State Management through
    

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76. • Rich with operators, Adheres to R&FP, exceptional handling, 

    lifecycle management, etc.
    viewModelScope.launch {
    flowOf(moviesClient.searchMoviesAsync(query).await())
    .map { Result.Success(it.results) }
    .catch {
    Result.Error(it.toApplicationError())
    }.collect {
    searchStates.postValue(it)
    }
    }
    State Management through
    

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77. • Rich with operators, Adheres to R&FP, exceptional handling, 

    lifecycle management, etc.
    viewModelScope.launch {
    flowOf(moviesClient.searchMoviesAsync(query).await())
    .map { Result.Success(it.results) }
    .catch {
    Result.Error(it.toApplicationError())
    }.collect {
    searchStates.postValue(it)
    }
    }
    State Management through
    

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78. • Rich with operators, Adheres to R&FP, exceptional handling, 

    lifecycle management, etc.
    viewModelScope.launch {
    flowOf(moviesClient.searchMoviesAsync(query).await())
    .map { Result.Success(it.results) }
    .catch {
    Result.Error(it.toApplicationError())
    }.collect {
    searchStates.postValue(it)
    }
    }
    State Management through
    

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79. • Rich with operators, Adheres to R&FP, exceptional handling, 

    lifecycle management, etc.
    viewModelScope.launch {
    flowOf(moviesClient.searchMoviesAsync(query).await())
    .map { Result.Success(it.results) }
    .catch {
    Result.Error(it.toApplicationError())
    }.collect {
    searchStates.postValue(it)
    }
    }
    State Management through
    

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80. • Rich with operators, Adheres to R&FP, exceptional handling, 

    lifecycle management, etc.
    viewModelScope.launch {
    flowOf(moviesClient.searchMoviesAsync(query).await())
    .map { Result.Success(it.results) }
    .catch {
    Result.Error(it.toApplicationError())
    }.collect {
    searchStates.postValue(it)
    }
    }
    UI Bindings?
    
    State Management through
    

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81. Conclusion
    

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82. Conclusion
    

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83. Thank you
    @droid_singh @amanjeetsingh150
    

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84. References
    • https://medium.com/the-kotlin-chronicle/coroutine-exceptions-3378f51a7d33
    • https://medium.com/@elizarov/
    • https://speakerdeck.com/krlrozov/kotlin-coroutines-flow-is-coming
    • https://speakerdeck.com/ragdroid/flowing-things-not-so-strange-in-the-mvi-world
    • https://github.com/amanjeetsingh150/CoroutinesRx
    • https://medium.com/capital-one-tech/coroutines-and-rxjava-an-asynchronicity-comparison-part-1-asynchronous-
    programming-e726a925342a
    • Kotlin Coroutines Slack Channel
    • https://github.com/android/plaid
    

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