Exploring Coroutines

Presentation about architecting a unidirectional data flow Android application using Kotlin's coroutines, with UI drive by state machines.

Presented at

- KotlinSP Meetup #10 (August/2019 - São Paulo, Brazil)

Transcript

1. Ubiratan Soares
   August / 2019
   EXPLORING
   COROUTINES
   

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2. How can we
   architect with
   Coroutines ?
   

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5. DataSource
   Use case ViewModel
   collaborates with
   

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6. DataSource
   Use case ViewModel
   External
   World
   User
   Interface
   Observable
   Observable Observable
   data flow format
   

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7. DataSource
   Use case ViewModel
   External
   World
   User
   Interface
   Observable
   Observable LiveData
   data flow format
   

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8. DataSource
   Use case ViewModel
   External
   World
   User
   Interface
   suspend fun (T)
   suspend fun (T) LiveData
   data flow format
   

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9. DataSource
   Use case ViewModel
   External
   World
   User
   Interface
   suspend fun (T)
   suspend fun (T) LiveData
   data flow format
   

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10. Unidirectional
    Data Flow
    

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11. Activity( ) : ViewProtocol doSomething ( ) Presenter
    View Protocol
    fun handle(d : Data)
    fun showLoading( )
    fun showError( )
    fun doSomething( )
    override fun handle(d : Data)
    override fun showLoading( )
    override fun showError( )
    doAnotherThing ( )
    fun doAnotherThing( )
    method call
    

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12. Activity( )
    doSomething ( )
    ViewModel
    fun doSomething( ) : LiveData
    fun handle(d : Data)
    fun showLoading( )
    fun showError( )
    doAnotherThing ( )
    fun doAnotherThing( ) : LiveData
    method call
    LiveData Observer
    

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13. Activity( ) doSomething ( ) ViewModel
    fun doSomething( ) : LiveData
    fun handle(d : Data)
    fun showLoading( )
    fun showError( )
    doAnotherThing ( )
    fun doAnotherThing( ) : LiveData
    method call
    fun justOneMoreThing( ) : LiveData
    justOneMoreThing ( )
    LiveData Observer
    

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14. Activity( ) doSomething ( ) ViewModel
    doAnotherThing ( )
    method call
    justOneMoreThing ( )
    LiveData Observer
    LiveData Observer
    LiveData Observer
    LiveData
    LiveData
    LiveData
    

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15. Activity( ) doSomething ( ) ViewModel
    doAnotherThing ( )
    method call
    justOneMoreThing ( )
    LiveData Observer
    LiveData Observer
    LiveData Observer
    LiveData
    LiveData
    LiveData
    

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17. DataSource
    Use case ViewModel
    External
    World
    User
    Interface
    suspend fun (T)
    suspend fun (T) suspend fun (T)
    data flow format
    

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18. DataSource
    Use case ViewModel
    External
    World
    User
    Interface
    suspend fun (T)
    suspend fun (T) suspend fun (T)
    data flow format
    How can we push
    multiple states
    to the View level ???
    

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25. DataSource
    Use case ViewModel
    External
    World
    User
    Interface
    suspend fun (T)
    suspend fun (T) Flow
    

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27. Activity( )
    handle(someInteraction)
    ViewModel
    method call
    FlowConsumer
    StateMachine
    fun handle(i : UserInteraction)
    bind( )
    fun bind( ) : Flow
    fun handle(d : Data)
    fun showLoading( )
    fun showError( )
    data flow format
    Flow
    

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28. Started
    bind( )
    

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29. Started Loading
    interaction
    (suspend wrapper)
    bind( )
    

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30. Started Loading
    Success
    interaction
    (suspend wrapper)
    bind( )
    suspend fun resumed
    

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31. Started Loading
    Error
    interaction
    (suspend wrapper)
    bind( )
    suspend fun resumed
    

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32. Started Loading
    Success
    Error
    interaction
    (suspend wrapper)
    bind( )
    suspend fun resumed
    suspend fun resumed
    

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33. Started Loading
    Success
    Error
    interaction
    (suspend wrapper)
    interaction
    (suspend wrapper)
    interaction
    (suspend wrapper)
    bind( )
    suspend fun resumed
    suspend fun resumed
    

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34. sealed class StateTransition {
    interface Parameters
    class Unparametrized internal constructor(
    val task: suspend () !" T
    ) : StateTransition()
    class Parametrized internal constructor(
    val task: suspend (Parameters) !" T,
    val parameters: Parameters
    ) : StateTransition()
    }
    

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35. sealed class StateTransition {
    interface Parameters
    class Unparametrized internal constructor(
    val task: suspend () !" T
    ) : StateTransition()
    class Parametrized internal constructor(
    val task: suspend (Parameters) !" T,
    val parameters: Parameters
    ) : StateTransition()
    }
    

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36. class StateMachine(
    private val container: StateContainer,
    private val executor: TaskExecutor
    ) {
    fun states() = container.observableStates()
    fun consume(execution: StateTransition) =
    executor.execute {
    wrapWithStates(execution)
    }
    // Continue on next slide
    }
    

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37. class StateMachine(#$%) {
    private suspend fun wrapWithStates(execution: StateTransition) {
    val first = executionStarted()
    moveTo(first)
    val next = executeWith(execution)
    moveTo(next)
    }
    private suspend fun executeWith(transition: StateTransition) =
    try {
    val execution =
    when (transition) {
    is Unparametrized !" transition.task.invoke()
    is Parametrized !" with(transition) { this.task.invoke(parameters) }
    }
    Success(execution)
    } catch (error: Throwable) {
    Failed(error)
    }
    }
    

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38. class StateMachine(#$%) {
    private suspend fun wrapWithStates(execution: StateTransition) {
    val first = executionStarted()
    moveTo(first)
    val next = executeWith(execution)
    moveTo(next)
    }
    private suspend fun executeWith(transition: StateTransition) =
    try {
    val execution =
    when (transition) {
    is Unparametrized !" transition.task.invoke()
    is Parametrized !" with(transition) { this.task.invoke(parameters) }
    }
    Success(execution)
    } catch (error: Throwable) {
    Failed(error)
    }
    }
    

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39. class StateMachine(#$%) {
    private suspend fun wrapWithStates(execution: StateTransition) {
    val first = executionStarted()
    moveTo(first)
    val next = executeWith(execution)
    moveTo(next)
    }
    private suspend fun executeWith(transition: StateTransition) =
    try {
    val execution =
    when (transition) {
    is Unparametrized !" transition.task.invoke()
    is Parametrized !" with(transition) { this.task.invoke(parameters) }
    }
    Success(execution)
    } catch (error: Throwable) {
    Failed(error)
    }
    }
    

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40. A complete
    data flow
    

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41. interface ChuckNorrisDotIO {
    @GET("/jokes/categories")
    suspend fun categories(): RawCategories
    @GET("/jokes/search")
    suspend fun search(@Query("query") query: String): RawSearch
    companion object {
    const val API_URL = "https:&'api.chucknorris.io"
    }
    }
    

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42. class FactsInfrastructure(
    private val rest: ChuckNorrisDotIO
    ) : RemoteFactsService {
    override suspend fun availableCategories() =
    managedExecution {
    rest.categories().asRelatedCategories()
    }
    override suspend fun fetchFacts(searchTerm: String) =
    managedExecution {
    rest.search(searchTerm).asChuckNorrisFacts()
    }
    }
    

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43. class FetchFacts(
    private val factsService: RemoteFactsService
    ) {
    suspend fun search(term: String) =
    when {
    term.isEmpty() !" throw EmptyTerm
    else !" {
    val facts = factsService.fetchFacts(term)
    if (facts.isEmpty()) throw NoResultsFound else facts
    }
    }
    }
    

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44. class FactsViewModel(
    private val factsFetcher: FetchFacts,
    private val queryManager: ManageSearchQuery,
    private val machine: StateMachine
    ) {
    fun bind() = machine.states()
    fun handle(interaction: UserInteraction) =
    interpret(interaction)
    .let { transition !"
    machine.consume(transition)
    }
    private fun interpret(interaction: UserInteraction) =
    when (interaction) {
    OpenedScreen, RequestedFreshContent !" StateTransition(()showFacts)
    else !" throw UnsupportedUserInteraction
    }
    

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45. private fun interpret(interaction: UserInteraction) =
    when (interaction) {
    OpenedScreen, RequestedFreshContent !" StateTransition(()showFacts)
    else !" throw UnsupportedUserInteraction
    }
    private suspend fun showFacts() =
    queryManager.actualQuery().let { query !"
    factsFetcher
    .search(query)
    .map { FactDisplayRow(it) }
    .let { rows !"
    FactsPresentation(query, rows)
    }
    }
    }
    

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46. private fun interpret(interaction: UserInteraction) =
    when (interaction) {
    OpenedScreen, RequestedFreshContent !" StateTransition(::showFacts)
    else !" throw UnsupportedUserInteraction
    }
    private suspend fun showFacts() =
    queryManager.actualQuery().let { query !"
    factsFetcher
    .search(query)
    .map { FactDisplayRow(it) }
    .let { rows !"
    FactsPresentation(query, rows)
    }
    }
    }
    

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47. class FactsActivity : AppCompatActivity(), KodeinAware {
    override fun onCreate(savedInstanceState: Bundle?) {
    super.onCreate(savedInstanceState)
    setContentView(R.layout.activity_main)
    setup()
    }
    private fun setup() {
    setSupportActionBar(factsToolbar)
    factsRecyclerView.layoutManager = LinearLayoutManager(this)
    factsSwipeToRefresh.setOnRefreshListener { refresh() }
    lifecycleScope.launch {
    viewModel.bind().collect { renderState(it) }
    }
    }
    

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48. private fun setup() {
    setSupportActionBar(factsToolbar)
    factsRecyclerView.layoutManager = LinearLayoutManager(this)
    factsSwipeToRefresh.setOnRefreshListener { refresh() }
    lifecycleScope.launch {
    viewModel.bind().collect { renderState(it) }
    }
    }
    private fun renderState(state: ViewState) =
    when (state) {
    is Failed !" handleError(state.reason)
    is Success !" showFacts(state.value)
    is Loading.FromEmpty !" startExecution()
    is Loading.FromPrevious !" showFacts(state.previous)
    is FirstLaunch !" loadFacts()
    }
    }
    

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49. private fun renderState(state: ViewState) =
    when (state) {
    is Failed !" handleError(state.reason)
    is Success !" showFacts(state.value)
    is Loading.FromEmpty !" startExecution()
    is Loading.FromPrevious !" showFacts(state.previous)
    is FirstLaunch !" loadFacts()
    }
    }
    private fun loadFacts() {
    viewModel.handle(OpenedScreen)
    }
    }
    

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50. Solving Lifecycles
    with Structured
    Concurrency
    

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51. State Machine
    TaskExecutor
    StateContainer
    collaborates with
    class StateMachine(
    private val container: StateContainer,
    private val executor: TaskExecutor
    ) {
    // Implementation
    }
    

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52. State Machine
    TaskExecutor
    StateContainer
    collaborates with
    The State Container registers the current state processed by the
    State Machine.
    The implementation is CoroutineScope-aware and uses a
    ConflatedBroadcastChannel as communication engine to
    propagate state to consumers.
    We can build a StateContainer instance with a CoroutineScope
    differente than the consumer’s scope
    

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53. State Machine
    TaskExecutor
    StateContainer
    collaborates with
    The task executor defines a model of execution for the state
    transition : either Concurrent or Synchronous
    

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54. interface TaskExecutor {
    fun execute(block: suspend TaskExecutor.() !" Unit): Job
    class Concurrent(
    private val scope: CoroutineScope,
    private val dispatcher: CoroutineDispatcher
    ) : TaskExecutor {
    override fun execute(block: suspend TaskExecutor.() !" Unit) =
    scope.launch(dispatcher) {
    block.invoke(this@Concurrent)
    }
    }
    class Synchronous(private val scope: CoroutineScope) : TaskExecutor {
    override fun execute(block: suspend TaskExecutor.() !" Unit) =
    runBlocking {
    scope.launch { block.invoke(this@Synchronous) }
    }
    }
    }
    

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55. interface TaskExecutor {
    fun execute(block: suspend TaskExecutor.() !" Unit): Job
    class Concurrent(
    private val scope: CoroutineScope,
    private val dispatcher: CoroutineDispatcher
    ) : TaskExecutor {
    override fun execute(block: suspend TaskExecutor.() !" Unit) =
    scope.launch(dispatcher) {
    block.invoke(this@Concurrent)
    }
    }
    class Synchronous(private val scope: CoroutineScope) : TaskExecutor {
    override fun execute(block: suspend TaskExecutor.() !" Unit) =
    runBlocking {
    scope.launch { block.invoke(this@Synchronous) }
    }
    }
    }
    

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56. Executor Coroutine
    (runs the suspend function)
    Consumer Coroutine
    (consume the states)
    Channel
    

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57. Executor Coroutine
    (runs the suspend function
    Scope = AAC ViewModel
    Consumer Coroutine
    (consume the states)
    Scope = Activity Lifecycle
    Channel
    

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58. class ConfigChangesAwareStateContainer : StateContainer, ViewModel() {
    private val broadcaster by lazy {
    ConflatedBroadcastChannel}
    override val emissionScope = viewModelScope
    override fun observableStates() = broadcaster.asFlow()
    override fun current(): ViewState = broadcaster.value
    override suspend fun store(state: ViewState) {
    broadcaster.send(state)
    }
    

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59. class ConfigChangesAwareStateContainer : StateContainer, ViewModel() {
    private val broadcaster by lazy {
    ConflatedBroadcastChannel}
    override val emissionScope = viewModelScope
    override fun observableStates() = broadcaster.asFlow()
    override fun current(): ViewState = broadcaster.value
    override suspend fun store(state: ViewState) {
    broadcaster.send(state)
    }
    Cold flow over
    Hot Channel
    

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60. class ConfigChangesAwareStateContainer : StateContainer, ViewModel() {
    private val broadcaster by lazy {
    ConflatedBroadcastChannel}
    override val emissionScope = viewModelScope
    override fun observableStates() = broadcaster.asFlow()
    override fun current(): ViewState = broadcaster.value
    override suspend fun store(state: ViewState) {
    broadcaster.send(state)
    }
    

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61. companion object {
    operator fun invoke(host: FragmentActivity): StateContainer {
    val f = object : ViewModelProvider.Factory {
    override fun create(klass: Class) =
    ConfigChangesAwareStateContainer() as Model
    }
    val keyClazz = ConfigChangesAwareStateContainer()class.java
    return ViewModelProviders.of(host, f)[keyClazz] as StateContainer
    }
    }
    }
    

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62. Testing like
    a pro
    

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63. class FetchCategoriesTests {
    private val categoriesCache = mock()
    private val remoteFacts = mock()
    private lateinit var usecase: FetchCategories
    private val categories = mutableListOf(
    RelatedCategory.Available("dev"),
    RelatedCategory.Available("code")
    )
    @Before fun `before each test`() {
    usecase = FetchCategories(categoriesCache, remoteFacts)
    }
    @Test fun `should fetch from cache from available`() {
    runBlocking {
    `given that remote service not available`()
    `given that cache returns categories`()
    assertThat(usecase.execute()).isEqualTo(categories)
    }
    }
    }
    

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64. internal class FactsInfrastructureTests {
    @get:Rule val rule = InfrastructureRule()
    private lateinit var infrastructure: FactsInfrastructure
    @Before fun `before each test`() {
    infrastructure = FactsInfrastructure(rule.api)
    }
    @Test fun `should fetch categories`() {
    rule.defineScenario(
    status = 200,
    response = loadFile("200_categories.json")
    )
    

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65. val expected = listOf(
    Available("career"),
    Available("celebrity"),
    Available("dev")
    )
    val categories = runBlocking {
    infrastructure.availableCategories()
    }
    assertThat(categories).isEqualTo(expected)
    }
    private fun simpleSearch() = runBlocking {
    infrastructure.fetchFacts("Norris")
    }
    }
    

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66. class FactsViewModelTests {
    @get:Rule val helper = CoroutinesTestHelper()
    private val fetchFacts = mock()
    private val manageQuery = mock()
    private lateinit var viewModel: FactsViewModel
    @Before fun `before each test`() {
    val stateMachine = StateMachine(
    executor = TaskExecutor.Synchronous(helper.scope),
    container = StateContainer.Unbounded(helper.scope)
    )
    viewModel = FactsViewModel(fetchFacts, manageQuery, stateMachine)
    }
    @Test fun `should report failure when fetching from remote`() {
    

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67. @Test fun `should report failure when fetching from remote`() {
    &' Given
    flowTest(viewModel.bind()) {
    triggerEmissions {
    &' When
    whenever(fetchFacts.search(anyString()))
    .thenAnswer { throw UnexpectedResponse }
    &' And
    viewModel.handle(UserInteraction.OpenedScreen)
    }
    afterCollect { emissions !"
    

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68. afterCollect { emissions !"
    &' Then
    val viewStates = listOf(
    FirstLaunch,
    Loading.FromEmpty,
    Failed(UnexpectedResponse)
    )
    assertThat(emissions).isEqualTo(viewStates)
    }
    }
    }
    }
    

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69. class FlowTest(private val parentJob: Job, private val emissions: List) {
    fun triggerEmissions(action: suspend () !" Job) {
    runBlocking { action().join() }
    }
    fun afterCollect(verification: (List) !" Unit) {
    parentJob.invokeOnCompletion {
    verification.invoke(emissions)
    }
    }
    companion object {
    fun flowTest(
    target: Flow,
    scope: CoroutineScope = GlobalScope,
    block: FlowTest.() !" Unit
    ) {
    target.test(scope, block)
    }
    }
    }
    

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70. class FlowTest(private val parentJob: Job, private val emissions: List) {
    fun triggerEmissions(action: suspend () !" Job) {
    runBlocking { action().join() }
    }
    fun afterCollect(verification: (List) !" Unit) {
    parentJob.invokeOnCompletion {
    verification.invoke(emissions)
    }
    }
    companion object {
    fun flowTest(
    target: Flow,
    scope: CoroutineScope = GlobalScope,
    block: FlowTest.() !" Unit
    ) {
    target.test(scope, block)
    }
    }
    }
    

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72. https://speakerdeck.com/ubiratansoares
    

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73. UBIRATAN
    SOARES
    Computer Scientist by ICMC/USP
    Software Engineer, curious guy
    Google Developer Expert for Android / Kotlin
    Teacher, speaker, etc, etc
    

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74. THANK YOU
    @ubiratanfsoares
    ubiratansoares.dev
    https://br.linkedin.com/in/ubiratanfsoares
    

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