KotlinConf 2017: View State Machine For Network Calls on Android

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VIEW STATE MACHINE FOR NETWORK CALLS ON ANDROID @MANDYBESS

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THOUGHTBOT

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WHAT IS A VIEW STATE MACHINE?

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BUILD AN APP TOGETHER ! "

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GAME OF CONES !

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MODELING !"!

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ICE CREAM - title - icon

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data class IceCream(val title: String, val iconUrl: String)

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! ➡ "

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MVP MODEL VIEW PRESENTER

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VIEW INTERFACE interface MainView { fun showTitle(title: String) fun showIcon(url: String) }

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PRESENTER class MainPresenter(val view: MainView) { fun onCreate() { val iceCream = ?? view.showTitle(iceCream.title) view.showIcon(iceCream.iconUrl) } }

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DATA STORE interface DataStore { fun fetchCone(): IceCream }

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PRESENTER + DATA STORE + class MainPresenter(val view: MainView, val dataStore: DataStore) { fun onCreate() { + val iceCream = dataStore.fetchCone() view.showTitle(iceCream.title) view.showIcon(iceCream.iconUrl) } }

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TESTING !

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PRESENTER TEST class MainPresenterTest { val view = mock() val dataStore = mock() val fakeIceCream = IceCream("Vanilla", "www.icecream.com") @Test fun test_onCreate() { //stub response whenever(dataStore.fetchCone()).thenReturn(fakeIceCream) val presenter = MainPresenter(view, dataStore) presenter.onCreate() verify(view).showTitle("Vanilla") verify(view).showIcon("www.icecream.com") verifyNoMoreInteractions(view) }

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NETWORK CALLS !"

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DATA STORE + RX interface DataStore { + fun fetchCone(): Observable }

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PRESENTER + RX class MainPresenter(val view: MainView, val dataStore: DataStore) { fun onCreate() { dataStore.fetchCone() .subscribeOn(Schedulers.io()) .observeOn(AndroidSchedulers.mainThread()) .subscribe( { iceCream -> // on success view.showTitle(iceCream.title) view.showIcon(iceCream.iconUrl) }, { error -> // on error } ) } }

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PRESENTER + RX class MainPresenter(val view: MainView, val dataStore: DataStore) { fun onCreate() { // loading?? dataStore.fetchCone() .subscribeOn(Schedulers.io()) .observeOn(AndroidSchedulers.mainThread()) .subscribe( { iceCream -> // on success view.showTitle(iceCream.title) view.showIcon(iceCream.iconUrl) }, { error -> // on error } ) } }

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VIEW INTERFACE + NETWORKING interface MainView { fun showTitle(title: String) fun showIcon(url: String) + fun showLoading() + fun hideLoading() + fun showError(errorMessage: String) }

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PRESENTER + NETWORKING class MainPresenter(val view: MainView, val dataStore: DataStore) { fun onCreate() { + view.showLoading() dataStore.fetchCone() .subscribeOn(Schedulers.io()) .observeOn(AndroidSchedulers.mainThread()) .subscribe( { iceCream -> + view.hideLoading() view.showTitle(iceCream.title) view.showIcon(iceCream.iconUrl) }, { error -> + view.hideLoading() + view.showError(error.message) } ) } }

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PRESENTER TEST + RX + NETWORKING ... @Test fun test_onCreate_success() { // stub response - whenever(dataStore.fetchCone()).thenReturn(fakeIceCream) + whenever(dataStore.fetchCone()).thenReturn(Observable.just(fakeIceCream)) val presenter = MainPresenter(view, dataStore) presenter.onCreate() + verify(view).showLoading() + verify(view).hideLoading() verify(view).showTitle("Vanilla") verify(view).showIcon("www.icecream.com") verifyNoMoreInteractions(view) }

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PRESENTER TEST + RX + NETWORKING ... @Test fun test_onCreate_error() { // stub response val errorMessage = "There was an error" whenever(dataStore.fetchCone()).thenReturn(Observable.error(Throwable(errorMessage))) val presenter = MainPresenter(view, dataStore) presenter.onCreate() verify(view).showLoading() verify(view).hideLoading() verify(view).showError(errorMessage) verifyNoMoreInteractions(view) }

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WE DID IT !

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UPDATES 1. Update our model 2. Update our view interface 3. Update our presenter 4. Update presenter tests

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MODEL UPDATE data class IceCream(val title: String, val iconUrl: String, val calorieCount: Int)

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VIEW INTERFACE + CALORIES interface MainView { fun showTitle(title: String) fun showIcon(url: String) fun showLoading() fun hideLoading() fun showError(errorMessage: String) + fun showCalorieCount(calorieCount: String) }

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PRESENTER + CALORIES class MainPresenter(val view: MainView, val dataStore: DataStore) { fun onCreate() { view.showLoading() dataStore.fetchCone() .subscribeOn(Schedulers.io()) .observeOn(AndroidSchedulers.mainThread()) .subscribe( { iceCream -> view.hideLoading() view.showTitle(iceCream.title) view.showIcon(iceCream.iconUrl) + view.showCalorieCount(context.getString(R.string.formatted_calorie_count, iceCream.calorieCount)) }, { error -> view.hideLding() view.showError(error.message) } ) } }

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PRESENTER TEST + CALORIES class MainPresenterTest { val view = mock() val dataStore = mock() val fakeIceCream = IceCream("Vanilla", "www.icecream.com", 120) @Test fun test_onCreate_success() { // stub response whenever(dataStore.fetchCone()).thenReturn(Observable.just(fakeIceCream)) val presenter = MainPresenter(view, dataStore) presenter.onCreate() verify(view).showLoading() verify(view).hideLoading() verify(view).showTitle("Vanilla") verify(view).showIcon("www.icecream.com") + verify(view).showCalories("120 Calories") verifyNoMoreInteractions(view) } ...

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PROGRESS REPORT !

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- used THE MVP PATTERN - added NETWORKING - updated THE UI

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Pros Cons UI updates are caught in tests Updates to the Presenter violate Open-Closed principle Networking view functions take away from the bigger picture of what's happening

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Pros Cons UI updates are caught in tests Updates to the Presenter violate Open-Closed principle Networking view functions take away from the bigger picture of what's happening

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HELLO ! NetworkingViewState

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NetworkingViewState sealed class NetworkingViewState { class Init() : NetworkingViewState() class Loading() : NetworkingViewState() class Success(val item: T) : NetworkingViewState() class Error(val errorMessage: String?) : NetworkingViewState() }

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MainView interface MainView { - fun showTitle(title: String) - fun showIcon(url: String) - fun showLoading() - fun hideLoading() - fun showError(errorMessage: String) - fun showCalorieCount(calorieCount: String) + var networkingViewState: NetworkingViewState }

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MainPresenter class MainPresenter(val view: MainView, val dataStore: DataStore) { fun onCreate() { - view.showLoading() + view.networkingViewState = NetworkingViewState.Loading() dataStore.fetchCone() .subscribeOn(Schedulers.io()) .observeOn(AndroidSchedulers.mainThread()) .subscribe( { iceCream -> - view.hideLoading() - view.showTitle(iceCream.title) - view.showIcon(iceCream.iconUrl) - view.showCalorieCount(R.string.formatted_calorie_count, iceCream.calorieCount) + view.networkingViewState = NetworkingViewState.Success(iceCream) }, { error -> - view.hideLoading() - view.showError(error.message) + view.networkingViewState = NetworkingViewState.Error(error.message) } ) } }

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MainPresenterTest ... @Test fun test_onCreate_success() { // stub response whenever(dataStore.fetchCone()).thenReturn(Observable.just(fakeIceCream)) val presenter = MainPresenter(view, dataStore) presenter.onCreate() - verify(view).showLoading() - verify(view).hideLoading() - verify(view).showTitle("Vanilla") - verify(view).showIcon("www.icecream.com") - verify(view).showCalorieCount(120 Calories) + verify(view).networkingViewState = isA() + verify(view).networkingViewState = isA>() verifyNoMoreInteractions(view) } }

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MainPresenterTest ... @Test fun test_onCreate_error() { // stub response val errorMessage = "There was an error" whenever(dataStore.fetchCone()).thenReturn(Observable.error(Throwable(errorMessage))) val presenter = MainPresenter(view, dataStore) presenter.onCreate() - verify(view).showLoading() - verify(view).hideLoading() - verify(view).showError() + verify(view).networkingViewState = isA() + verify(view).networkingViewState = isA

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OUR VIEW TESTS ARE HOMELESS !"

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PRESENTER + VIEW MODEL class MainPresenter(val view: MainView, val dataStore: DataStore) { fun onCreate() { view.networkingViewState = NetworkingViewState.Loading() dataStore.fetchCone() .subscribeOn(Schedulers.io()) .observeOn(AndroidSchedulers.mainThread()) .subscribe( { iceCream -> - view.networkingViewState = NetworkingViewState.Success(iceCream) + view.networkingViewState = NetworkingViewState.Success(IceCreamViewModel(iceCream, context)) }, { error -> view.networkingViewState = NetworkingViewState.Error(error.message) } ) } }

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VIEW MODEL class IceCreamViewModel(val iceCream: IceCream, val context: Context) { fun title(): String { return iceCream.title } fun iconUrl(): String { return iceCream.iconUrl } fun calorieCount(): String { return context.getString(R.string.formatted_calorie_count, iceCream.calorieCount) } }

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VIEW MODEL TEST class IceCreamViewModelTest { val fakeIceCream = IceCream("Vanilla", "www.icecream.com", 120) val context: Context @Test fun testTitle() { val viewModel = IceCreamViewModel(context, fakeIceCream) val expected = "Vanilla" val actual = viewModel.title() assertEquals(expected, actual) } }

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MAIN ACTIVITY class MainActivity : AppCompatActivity(), MainView { override fun onCreate(savedInstanceState: Bundle?) { super.onCreate(savedInstanceState) setContentView(R.layout.activity_main) } override var networkingViewState: NetworkingViewState get() = TODO() set(value) {} }

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HELLO ! PROPERTY DELEGATES

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Delegates.observable

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ObservableProperty public abstract class ObservableProperty(initialValue: T) : ReadWriteProperty { private var value = initialValue protected open fun beforeChange(property: KProperty<*>, oldValue: T, newValue: T): Boolean = true protected open fun afterChange (property: KProperty<*>, oldValue: T, newValue: T): Unit {} public override fun getValue(thisRef: Any?, property: KProperty<*>): T { return value } public override fun setValue(thisRef: Any?, property: KProperty<*>, value: T) { val oldValue = this.value if (!beforeChange(property, oldValue, value)) { return } this.value = value afterChange(property, oldValue, value) } }

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MAIN ACTIVITY + PROPERTY DELEGATE class MainActivity : AppCompatActivity(), MainView { override fun onCreate(savedInstanceState: Bundle?) { super.onCreate(savedInstanceState) setContentView(R.layout.activity_main) } override var networkingViewState: NetworkingViewState by Delegates.observable( Init(), { property, oldValue, newValue -> }) }

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! LINKS ! @mandybess " www.mandybess.com # https://robots.thoughtbot.com/android-networking-view-state $ https://speakerdeck.com/mandybess