36・15 Cash App

1300 modules. 50 developers. 40 million customers.
This Android application, what does it look like?
It looks like Cash App.
We have the opportunity to discover, to inspect, to dive indeed into the internal current state of Cash App. No rug unturned, we will reveal it all: tech stack, open-source, APIs, architecture, development process, design system, testing, navigation, CI.
Our Android application is modern, flexible, and reliable. We shall discover how it gets done.

Transcript

1. 36ŋ15
2. Cash App
3. Cash App
4. Cash App
5. Cash App • 60~ developpers • 1_350~ modules • 160_000~ lines of Kotlin
6. Protobuf Backend DB Network Presenter View Screen
7. Protobuf
8. • API contract • Code generation • Efficient Protobuf
9. Protobuf
10. Protobuf
11. Network
12. Network
13. Network
14. Network
15. Database
16. Database
17. Database
18. • Service • Manager • Syncer • Repository Backend
19. interface InvestingAppService { @POST("/2.0/cash/investing/get-discovery") suspend fun getDiscovery( @Body request: GetDiscoveryRequest, ): ApiResult<GetDiscoveryResponse> @POST("/2.0/cash/investing/get-customer-settings") fun getCustomerSettings( @Body request: GetCustomerSettingsRequest, ): Single<ApiResult<GetCustomerSettingsResponse>> } Backend
20. sealed class ApiResult<out T : Any> { data class Success<T : Any>(val response: T) : ApiResult<T>() sealed class Failure : ApiResult<Nothing>() { data class NetworkFailure(val error: Throwable) : Failure() data class HttpFailure( val code: Int, val responseHeaderDate: Date? = null, ) : Failure() } } Backend
21. interface InvestmentEntities { fun discoveryStocks(forSearch: Boolean): Flow<DiscoverySections> fun stockDetails(token: InvestmentEntityToken): Flow<StockDetails> } Backend
22. interface InvestmentEntities { fun discoveryStocks(forSearch: Boolean): Flow<DiscoverySections> fun stockDetails(token: InvestmentEntityToken): Flow<StockDetails> } class RealInvestmentEntities @Inject internal constructor( private val cashDatabase: CashDatabase, @Io private val ioDispatcher: CoroutineContext, ) : InvestmentEntities { override fun discoveryStocks( forSearch: Boolean, ): Flow<DiscoverySections> { return cashDatabase.investingDiscoveryQueries .selectDiscoveries(in_search_category = false) .asFlow() .mapToList(ioDispatcher) .f l atMapLatest { entities -> Backend
23. interface InvestmentEntities { fun discoveryStocks(forSearch: Boolean): Flow<DiscoverySections> fun stockDetails(token: InvestmentEntityToken): Flow<StockDetails> } class FakeInvestmentEntities : InvestmentEntities { val discoveryAll = MutableSharedFlow<DiscoverySections>(replay = 1) val discoveryForSearch = MutableSharedFlow<DiscoverySections>(replay = 1) override fun discoveryStocks( forSearch: Boolean, ): Flow<DiscoverySections> { return if (forSearch) discoveryForSearch else discoveryAll } Backend
24. interface InvestingStateManager { @Composable fun investingStates(): InvestingState } Backend
25. interface InvestingStateManager { @Composable fun investingStates(): InvestingState } class RealInvestingStateManager @Inject constructor( database: CashAccountDatabase, @Io private val ioDispatcher: CoroutineContext, ) : InvestingStateManager { private val stateQueries = database.investingStateQueries @Composable override fun investingStates(): InvestingState { val dbInvestState: Investing_state? by remember { stateQueries.select().asFlow().mapToOne(ioDispatcher) }.collectAsState(null) // Do things imperative style. return investState } Backend
26. interface InvestingStateManager { @Composable fun investingStates(): InvestingState } class FakeInvestingStateManager( defaultModel: InvestingState = DEFAULT_STATE, ) : InvestingStateManager { var investingStates by mutableStateOf(defaultModel) @Composable override fun investingStates(): InvestingState { return investingStates } } Backend
27. MVW Architecture
28. Model-View-Whatever
29. Model-View-Whatever • Unidirectional Data Flow • Single source of truth • Immutability • Side-effect isolation
30. Protobuf Backend DB Network Presenter View MVW
31. Presenter View MVW
32. Presenter View ViewEvent ViewModel MVW
33. ViewEventɾViewModel sealed class DependentWelcomeViewEvent { data object ButtonClicked : DependentWelcomeViewEvent() data class Close(val someData: String) : DependentWelcomeViewEvent() } data class DependentWelcomeViewModel( val toolbarTitle: String, val title: String, val buttonLabel: String, )
34. ViewEventɾProtip
35. ViewEventɾProtip sealed class LeftViewEvent { data object Left : LeftViewEvent() } sealed class RightViewEvent { data object Right : RightViewEvent() } sealed class CommonViewEvent { data object Yes : CommonViewEvent() data object No : CommonViewEvent() }
36. ViewEventɾProtip sealed class LeftViewEvent { data object Left : LeftViewEvent() data class CommonEvent( val event: CommonViewEvent, ) : LeftViewEvent() } sealed class RightViewEvent { data object Right : RightViewEvent() data class CommonEvent( val event: CommonViewEvent, ) : RightViewEvent() } sealed class CommonViewEvent { data object Yes : CommonViewEvent() data object No : CommonViewEvent() }
37. ViewEventɾProtip sealed class LeftViewEvent { data object Left : LeftViewEvent() data class CommonEvent( val event: CommonViewEvent, ) : LeftViewEvent() } sealed class RightViewEvent { data object Right : RightViewEvent() data class CommonEvent( val event: CommonViewEvent, ) : RightViewEvent() } sealed class CommonViewEvent { data object Yes : CommonViewEvent() data object No : CommonViewEvent() } fun handleEvent(event: LeftViewEvent) { when (event) { is Left -> TODO() is CommonEvent -> when (event.event) { is Yes -> TODO() is No -> TODO() } } }
38. ViewEventɾProtip sealed interface LeftViewEvent { data object Left : LeftViewEvent data class CommonEvent( val event: CommonViewEvent, ) : LeftViewEvent } sealed interface RightViewEvent { data object Right : RightViewEvent data class CommonEvent( val event: CommonViewEvent, ) : RightViewEvent } sealed interface CommonViewEvent { data object Yes : CommonViewEvent data object No : CommonViewEvent } fun handleEvent(event: LeftViewEvent) { when (event) { is Left -> TODO() is CommonEvent -> when (event.event) { is Yes -> TODO() is No -> TODO() } } }
39. ViewEventɾProtip sealed interface LeftViewEvent { data object Left : LeftViewEvent } sealed interface RightViewEvent { data object Right : RightViewEvent } sealed interface CommonViewEvent : LeftViewEvent, RightViewEvent { data object Yes : CommonViewEvent data object No : CommonViewEvent } fun handleEvent(event: LeftViewEvent) { when (event) { is Left -> TODO() is CommonEvent -> when (event.event) { is Yes -> TODO() is No -> TODO() } } }
40. ViewEventɾProtip sealed interface LeftViewEvent { data object Left : LeftViewEvent } sealed interface RightViewEvent { data object Right : RightViewEvent } sealed interface CommonViewEvent : LeftViewEvent, RightViewEvent { data object Yes : CommonViewEvent data object No : CommonViewEvent } fun handleEvent(event: LeftViewEvent) { when (event) { is Left -> TODO() is Yes -> TODO() is No -> TODO() } }
41. ViewEventɾProtip sealed interface LeftViewEvent { data object Left : LeftViewEvent } sealed interface RightViewEvent { data object Right : RightViewEvent } sealed interface CommonViewEvent : LeftViewEvent, RightViewEvent { data object Yes : CommonViewEvent data object No : CommonViewEvent } fun handleEvent(event: LeftViewEvent) { when (event) { is Left -> TODO() is Yes -> TODO() is No -> TODO() } } fun handleEvent(event: RightViewEvent) { when (event) { is Right -> TODO() is Yes -> TODO() is No -> TODO() } }
42. interface Presenter<UiModel : Any, UiEvent : Any> { } Presenter
43. interface Presenter<UiModel : Any, UiEvent : Any> { val models: Flow<UiModel> fun sendEvent(event: UiEvent) } Presenter
44. interface Presenter<UiModel : Any, UiEvent : Any> { fun start( scope: CoroutineScope, ): Binding<UiModel, UiEvent> interface Binding<UiModel : Any, UiEvent : Any> { val models: Flow<UiModel> fun sendEvent(event: UiEvent) } } Presenter
45. interface Presenter<UiModel : Any, UiEvent : Any> { fun start( scope: CoroutineScope, ): Binding<UiModel, UiEvent> interface Binding<UiModel : Any, UiEvent : Any> { // TODO: Change to StateFlow once all presenters can provide an initial value. val models: Flow<UiModel> fun sendEvent(event: UiEvent) } } Presenter
46. @Deprecated("Use MoleculePresenter instead.") fun interface RxPresenter<UiEvent : Any, UiModel : Any> : ObservableTransformer<UiEvent, UiModel> @Deprecated("Use MoleculePresenter instead.") interface CoroutinePresenter<UiEvent : Any, UiModel : Any> { } interface MoleculePresenter<UiModel : Any, UiEvent : Any> { @Composable fun models( events: Flow<UiEvent>, ): UiModel } Presenter
47. @Deprecated("Use MoleculePresenter instead.") fun interface RxPresenter<UiEvent : Any, UiModel : Any> : ObservableTransformer<UiEvent, UiModel> @Deprecated("Use MoleculePresenter instead.") interface CoroutinePresenter<UiEvent : Any, UiModel : Any> { } interface MoleculePresenter<UiModel : Any, UiEvent : Any> { @Composable fun models( events: Flow<UiEvent>, ): UiModel } Presenter
48. @Deprecated("Use MoleculePresenter instead.") fun interface RxPresenter<UiEvent : Any, UiModel : Any> : ObservableTransformer<UiEvent, UiModel> @Deprecated("Use MoleculePresenter instead.") interface CoroutinePresenter<UiEvent : Any, UiModel : Any> { } interface MoleculePresenter<UiModel : Any, UiEvent : Any> { @Composable fun models( events: Flow<UiEvent>, ): UiModel } Presenter
49. interface MoleculePresenter<UiModel : Any, UiEvent : Any> { @Composable fun models( events: Flow<UiEvent>, ): UiModel } Presenter
50. class DependentWelcomePresenter( database: CashDatabase, private val stringManager: StringManager, @Io private val ioDispatcher: CoroutineContext, ) : MoleculePresenter<DependentWelcomeViewModel, DependentWelcomeViewEvent> { @Composable override fun models(events: Flow<DependentWelcomeViewEvent>): DependentWelcomeViewModel { LaunchedE f fect(events) { events.collect { event -> when (event) { ButtonClicked -> { // Start flow. } Close -> { // Navigate back. } } }} val toolbarTitle by remember { database.stateQueries.select().asFlow().mapToOne(ioDispatcher).map { it.toolbar_title } }.collectAsState(stringManager[R.string.investing_tab_title]) return DependentWelcomeViewModel( toolbarTitle = toolbarTitle, title = stringManager[R.string.dependent_welcome_title], buttonLabel = stringManager[R.string.dependent_welcome_button_label], ) } } Presenter
51. Molecule
52. /** * Create a [Flow] which will continually recompose `body` to produce * a stream of [T] values when collected. */ fun <T> moleculeFlow( clock: RecompositionClock, body: @Composable () -> T, ): Flow<T> { // Stuff. } enum class RecompositionClock { ContextClock, Immediate, } Molecule
53. /** * Launch a coroutine into this [CoroutineScope] which will * continually recompose `body` to produce a [StateFlow] stream * of [T] values. */ fun <T> CoroutineScope.launchMolecule( clock: RecompositionClock, body: @Composable () -> T, ): StateFlow<T> { // Stuff. } enum class RecompositionClock { ContextClock, Immediate, } Molecule
54. val flow: Flow<ProfileModel> = moleculeFlow(Immediate) { profilePresenter(userFlow, balanceFlow) } val stateFlow: StateFlow<ProfileModel> = scope.launchMolecule(Immediate) { profilePresenter(userFlow, balanceFlow) } Molecule
55. interface Ui<UiModel : Any, UiEvent : Any> { } View
56. interface Ui<UiModel : Any, UiEvent : Any> { fun interface EventReceiver<UiEvent> { fun sendEvent(event: UiEvent) } fun setEventReceiver(receiver: EventReceiver<UiEvent>) } View
57. interface Ui<UiModel : Any, UiEvent : Any> { fun interface EventReceiver<UiEvent> { fun sendEvent(event: UiEvent) } fun setEventReceiver(receiver: EventReceiver<UiEvent>) fun setModel(model: UiModel) } View
58. class DependentView(context: Context) : View(context), Ui<DependentViewModel, DependentViewEvent> { override fun setEventReceiver(receiver: EventReceiver<DependentViewEvent>) { button.setOnClickListener { receiver.sendEvent(ButtonClicked) } toolbar.setNavigationOnClickListener { receiver.sendEvent(Close) } } override fun setModel(model: DependentWelcomeViewModel) { toolbar.title = model.toolbarTitle titleView.text = model.title button.text = model.buttonLabel } } View
59. import androidx.compose.ui.platform.AbstractComposeView abstract class ComposeUiView<UiModel : Any, UiEvent : Any>( context: Context, attrs: AttributeSet? = null, ) : AbstractComposeView(context, attrs), Ui<UiModel, UiEvent> { @Composable abstract fun Content( model: UiModel?, onEvent: (UiEvent) -> Unit, ) } View
60. class SettingView( context: Context, ) : ComposeUiView<SettingViewModel, SettingViewEvent>(context) { @Composable override fun Content( model: SettingViewModel?, onEvent: (SettingViewEvent) -> Unit, ) { // We can require it because our presenter emits synchronously. requireNotNull(model) SettingViewContent(model, onEvent) } } View
61. Protobuf Backend DB Network Presenter View Testing
62. Protobuf Backend DB Network Presenter View Testing
63. Testing
64. @get:Rule val temporaryDatabase = TemporaryDatabase() @Test fun `discovery starts with no prices`() = runTest { investmentEntities().discoveryStocks(forSearch = false).test { assertThat(awaitItem()).isEqualTo(expected) entityPriceRefresher.currentPrices.onNext(amazonPrice) assertThat(awaitItem()).isEqualTo(otherExpected) ensureAllEventsConsumed() } } Testing
65. open class TurbinesRule( val turbines: Turbines = Turbines(), ) : ExternalResource() { override fun after() { turbines.assertEmpty() } } Testing
66. class FakeNavigator internal constructor() : Navigator { private val channels = Turbines() private val navigatedScreens = channels.create<Screen>() override fun goTo(screen: Screen) { navigatedScreens.add(screen) } suspend fun awaitNextScreen() = navigatedScreens.awaitItem() } Testing
67. class FakeNavigator internal constructor() : Navigator { class Rule( val navigator: FakeNavigator = FakeNavigator(), ) : TurbinesRule(navigator.channels) private val channels = Turbines() private val navigatedScreens = channels.create<Screen>() override fun goTo(screen: Screen) { navigatedScreens.add(screen) } suspend fun awaitNextScreen() = navigatedScreens.awaitItem() } Testing
68. class DependentWelcomePresenterTest { @get:Rule val navigatorRule = FakeNavigatorRule() private val navigator = navigatorRule.navigator private val stringManager = FakeStringManager( R.string.title to "Welcome", R.string.button_label to "Next", ) private val presenter = DependentWelcomePresenter( stringManager = stringManager, navigator = navigator, ) @Test fun models(): Unit = runTest { presenter.test { assertThat(awaitItem()).isEqualTo(expected)) } Testing
69. ) private val presenter = DependentWelcomePresenter( stringManager = stringManager, navigator = navigator, ) @Test fun models(): Unit = runTest { presenter.test { assertThat(awaitItem()).isEqualTo(expected)) } } @Test fun `button clicks navigates`() = runTest { presenter.test { skipItem("Model") sendEvent(ButtonClicked) assertThat(navigator.awaitNextScreen()).isEqualTo(expected) } }
70. class RealInvestingStateManagerTest { @get:Rule val temporaryDatabase = TemporaryDatabase() private val manager = RealInvestingStateManager( database = temporaryDatabase.cashDatabase, ioContext = EmptyCoroutineContext, ) @Test fun defaultState() = runTest { manager.test { assertThat(awaitItem()).isEqualTo(Loading) // Data has been fetched from the DB. assertThat(awaitItem()).isEqualTo(expected) } } companion object { private suspend fun InvestingStateManager.test(
71. private val manager = RealInvestingStateManager( database = temporaryDatabase.cashDatabase, ioContext = EmptyCoroutineContext, ) @Test fun defaultState() = runTest { manager.test { assertThat(awaitItem()).isEqualTo(Loading) // Data has been fetched from the DB. assertThat(awaitItem()).isEqualTo(expected) } } companion object { private suspend fun InvestingStateManager.test( validate: suspend ReceiveTurbine<InvestingState>.() -> Unit, ) { moleculeFlow(Immediate) { investingStates() } .test { validate() } } } }
72. Ui Testing
73. Ui Testing
74. class DependentWelcomeViewTest() { @get:Rule val paparazzi = Paparazzi( theme = “Theme.Cash.Default", ) @Test fun tests() { val view = DependentWelcomeView(context = paparazzi.context) view.setEventReceiver {} view.setModel( DependentWelcomeViewModel( toolbarTitle = "Stocks", title = "Stocks are now available for anyone", buttonLabel = "Next", ), ) paparazzi.snapshot(view) } } Ui Testing
75. enum class AccessibilityTextSize(val scale: Float) { NORMAL(scale = 1f), LARGE(scale = 2f), } enum class DesignTheme(val theme: Theme, val colors: Colors) { Light(MooncakeLight, Colors.light), Dark(MooncakeDark, Colors.dark), ; val provide: Context.() -> ThemeInfo = {..} } class DependentWelcomeViewTest() { @get:Rule val paparazzi = Paparazzi( theme = “Theme.Cash.Default", ) Ui Testing
76. Dark(MooncakeDark, Colors.dark), ; val provide: Context.() -> ThemeInfo } } @RunWith(TestParameterInjector::class) class DependentWelcomeViewTest( @TestParameter private val design: DesignTheme, @TestParameter private val accessibilityTextSize: AccessibilityTextSize, ) { @get:Rule val paparazzi = Paparazzi( theme = "Theme.Cash.Default", ) @Test fun tests() { val view = DependentWelcomeView(context = paparazzi.context).apply { setBackgroundColor(themeInfo().colorPalette.background) } view.setEventReceiver {} view.setModel( DependentWelcomeViewModel( toolbarTitle = "Stocks", title = "Stocks are now available for anyone", buttonLabel = "Next",
77. val provide: Context.() -> ThemeInfo } } @RunWith(TestParameterInjector::class) class DependentWelcomeViewTest( @TestParameter private val design: DesignTheme, @TestParameter private val accessibilityTextSize: AccessibilityTextSize, ) { @get:Rule val paparazzi = Paparazzi( theme = "Theme.Cash.Default", deviceConfig = DeviceConfig.PIXEL_4 .copy(fontScale = accessibilityTextSize.scale), ) private val context: Context by lazy { val themeInfo = design.provide(paparazzi.context) paparazzi.context.wrapWithTheme { themeInfo } } @Test fun tests() { val view = DependentWelcomeView(context = context).apply { setBackgroundColor(themeInfo().colorPalette.background) } view.setEventReceiver {} view.setModel(
78. Ui Testing
79. Ui Testing
80. - Write tests. Ui Testing
81. - Write tests. - Record snapshots: ./gradlew module:recordPaparazziDebug Ui Testing
82. - Write tests. - Record snapshots: ./gradlew module:recordPaparazziDebug - Check snapshots into the repository. Ui Testing
83. - Write tests. - Record snapshots: ./gradlew module:recordPaparazziDebug - Check snapshots into the repository. - Run verify task on CI: ./gradlew module:verifyPaparazziDebug Ui Testing
91. Navigation
92. interface Screen : Parcelable Navigation
93. interface Screen : Parcelable @Parcelize data class StockDetails( val entityToken: EntityToken, ) : Screen Navigation
94. interface Navigator { fun goTo(screen: Screen) } Navigation
95. interface Navigator { fun goTo(screen: Screen) } LaunchedE f fect(events) { events.collect { event -> when (event) { ButtonClicked -> { // Start flow. } Close -> { // Navigate. } } } } Navigation
96. interface Navigator { fun goTo(screen: Screen) } LaunchedE f fect(events) { events.collect { event -> when (event) { ButtonClicked -> { // Start flow. } Close -> { navigator.goTo(SomeScreen()) } } } } Navigation
97. interface ViewFactory { fun createView( screen: Screen, parent: ViewGroup, ): Ui<*, *>? } interface PresenterFactory { fun create( screen: Screen, navigator: Navigator, ): Presenter<*, *>? } interface TransitionFactory { fun createTransition( fromScreen: Screen, fromView: View, toScreen: Screen, toView: View, parent: ViewGroup, ): Animator? = null }
98. fun MoleculePresenter<UiEvent, UiModel>.asPresenter() : Presenter<UiModel, UiEvent> { return object : Presenter<UiModel, UiEvent> { override fun start( scope: CoroutineScope, ): Presenter.Binding<UiModel, UiEvent> { // Stuff. } } }
99. class InvestingViewFactory @Inject internal constructor( private val customOrder: InvestingCustomOrderView.Factory, private val featureFlag: FeatureFlagManager, ) : BroadwayViewFactory { override fun createView(screen: Screen, context: Context, parent: ViewGroup): View? { val view = when (screen) { is DependentWelcomeScreen -> DependentWelcomeView(context) is CustomOrderScreen -> customOrder.build(context) is NotificationSettings -> if (featureFlag.something()) { InvestingNotificationSettingsNew(context) } else { InvestingNotificationSettingsLegacy(context) } else -> XmlFactory.inflate( context = context, layoutResId = when (screen) { is InvestingHome -> R.layout.investing_home else -> return null }, parent = parent, ) } return view
100. class InvestingPresenterFactory @Inject internal constructor( private val notificationSettingsPresenter: InvestingNotificationSettingsPresenter.Factory, private val customOrderPresenter: InvestingCustomOrderPresenter.Factory, private val investingHomePresenter: InvestingHomePresenter.Factory, private val dependentWelcomePresenter: DependentWelcomePresenter.Factory, ) : PresenterFactory { override fun create( screen: Screen, navigator: Navigator, ): Presenter<*, *>? { return when (screen) { is DependentWelcomeScreen -> dependentWelcomePresenter.construct(navigator).asPresenter( is CustomOrderScreen -> customOrderPresenter.create(screen, navigator).asPresenter() is InvestingHome -> investingHomePresenter.create(navigator, screen).asPresenter() is NotificationSettings -> notificationSettingsPresenter.create(screen, navigator).asPre else -> null } } }
101. class Broadway( private val viewFactories: List<ViewFactory> = listOf(), private val transitionFactories: List<TransitionFactory> = listOf(), private val presenterFactories: List<PresenterFactory> = listOf(), ) { fun createViewOrNull(...): ScreenView? { return viewFactories.asSequence().mapNotNull { it.createView(screen, themedContext, parent) }.firstOrNull() } fun createTransition(...): Animator? { return transitionFactories.asSequence().mapNotNull { it.createTransition(fromScreen, fromView, toScreen, toView, parent) }.firstOrNull() } fun createPresenter(screen: Screen, navigator: Navigator): Presenter<*, *>? { return presenterFactories.asSequence().mapNotNull { it.create(screen, navigator) }.firstOrNull() } }
102. class RealNavigator( private val broadway: Broadway, ) : FrameLayout(context), Navigator { fun goTo(screen: Screen) { val presenter = broadway.createPresenter(screen, navigator = this) val ui = broadway.createUi(screen, context) bindAndAttachAndSwapAndStuff(ui, presenter) } }
103. - navigator.goTo(SomeScreen)
104. - navigator.goTo(SomeScreen) - Determine the screen type: full, overlay, meta.
105. - navigator.goTo(SomeScreen) - Determine the screen type: full, overlay, meta. - Back stack management
106. - navigator.goTo(SomeScreen) - Determine the screen type: full, overlay, meta. - Back stack management - Tear down old presenter
107. - navigator.goTo(SomeScreen) - Determine the screen type: full, overlay, meta. - Back stack management - Tear down old presenter - currentPresenterScope.cancel()
108. - navigator.goTo(SomeScreen) - Determine the screen type: full, overlay, meta. - Back stack management - Tear down old presenter - currentPresenterScope.cancel() - Save UI state
109. - navigator.goTo(SomeScreen) - Determine the screen type: full, overlay, meta. - Back stack management - Tear down old presenter - currentPresenterScope.cancel() - Save UI state - Spin up new presenter
110. - navigator.goTo(SomeScreen) - Determine the screen type: full, overlay, meta. - Back stack management - Tear down old presenter - currentPresenterScope.cancel() - Save UI state - Spin up new presenter - val newPresenter = presenterFactories.asSequence() .mapNotNull { it.create(screen, navigator) } .firstOrNull()
111. - navigator.goTo(SomeScreen) - Determine the screen type: full, overlay, meta. - Back stack management - Tear down old presenter - currentPresenterScope.cancel() - Save UI state - Spin up new presenter - val newPresenter = presenterFactories.asSequence() .mapNotNull { it.create(screen, navigator) } .firstOrNull() - newPresenter.start(scope)
112. - navigator.goTo(SomeScreen) - Determine the screen type: full, overlay, meta. - Back stack management - Tear down old presenter - currentPresenterScope.cancel() - Save UI state - Spin up new presenter - val newPresenter = presenterFactories.asSequence() .mapNotNull { it.create(screen, navigator) } .firstOrNull() - newPresenter.start(scope) - Create UI
113. - navigator.goTo(SomeScreen) - Determine the screen type: full, overlay, meta. - Back stack management - Tear down old presenter - currentPresenterScope.cancel() - Save UI state - Spin up new presenter - val newPresenter = presenterFactories.asSequence() .mapNotNull { it.create(screen, navigator) } .firstOrNull() - newPresenter.start(scope) - Create UI - val newUi = uiFactories.asSequence() .mapNotNull { it.createUi(screen, themedContext, parent) } .firstOrNull()
114. - navigator.goTo(SomeScreen) - Determine the screen type: full, overlay, meta. - Back stack management - Tear down old presenter - currentPresenterScope.cancel() - Save UI state - Spin up new presenter - val newPresenter = presenterFactories.asSequence() .mapNotNull { it.create(screen, navigator) } .firstOrNull() - newPresenter.start(scope) - Create UI - val newUi = uiFactories.asSequence() .mapNotNull { it.createUi(screen, themedContext, parent) } .firstOrNull() - Restore UI state if adequate
115. - navigator.goTo(SomeScreen) - Determine the screen type: full, overlay, meta. - Back stack management - Tear down old presenter - currentPresenterScope.cancel() - Save UI state - Spin up new presenter - val newPresenter = presenterFactories.asSequence() .mapNotNull { it.create(screen, navigator) } .firstOrNull() - newPresenter.start(scope) - Create UI - val newUi = uiFactories.asSequence() .mapNotNull { it.createUi(screen, themedContext, parent) } .firstOrNull() - Restore UI state if adequate - Bind UI to Presenter
116. - navigator.goTo(SomeScreen) - Determine the screen type: full, overlay, meta. - Back stack management - Tear down old presenter - currentPresenterScope.cancel() - Save UI state - Spin up new presenter - val newPresenter = presenterFactories.asSequence() .mapNotNull { it.create(screen, navigator) } .firstOrNull() - newPresenter.start(scope) - Create UI - val newUi = uiFactories.asSequence() .mapNotNull { it.createUi(screen, themedContext, parent) } .firstOrNull() - Restore UI state if adequate - Bind UI to Presenter - newPresenterScope.launch { ui.setEventReceiver(presenter::sendEvent) presenter.models.collect(ui::setModel) }
117. - navigator.goTo(SomeScreen) - Determine the screen type: full, overlay, meta. - Back stack management - Tear down old presenter - currentPresenterScope.cancel() - Save UI state - Spin up new presenter - val newPresenter = presenterFactories.asSequence() .mapNotNull { it.create(screen, navigator) } .firstOrNull() - newPresenter.start(scope) - Create UI - val newUi = uiFactories.asSequence() .mapNotNull { it.createUi(screen, themedContext, parent) } .firstOrNull() - Restore UI state if adequate - Bind UI to Presenter - newPresenterScope.launch { ui.setEventReceiver(presenter::sendEvent) presenter.models.collect(ui::setModel) } - Deliver results
118. - navigator.goTo(SomeScreen) - Determine the screen type: full, overlay, meta. - Back stack management - Tear down old presenter - currentPresenterScope.cancel() - Save UI state - Spin up new presenter - val newPresenter = presenterFactories.asSequence() .mapNotNull { it.create(screen, navigator) } .firstOrNull() - newPresenter.start(scope) - Create UI - val newUi = uiFactories.asSequence() .mapNotNull { it.createUi(screen, themedContext, parent) } .firstOrNull() - Restore UI state if adequate - Bind UI to Presenter - newPresenterScope.launch { ui.setEventReceiver(presenter::sendEvent) presenter.models.collect(ui::setModel) } - Deliver results - Attach UI and runs transition
119. - navigator.goTo(SomeScreen) - Determine the screen type: full, overlay, meta. - Back stack management - Tear down old presenter - currentPresenterScope.cancel() - Save UI state - Spin up new presenter - val newPresenter = presenterFactories.asSequence() .mapNotNull { it.create(screen, navigator) } .firstOrNull() - newPresenter.start(scope) - Create UI - val newUi = uiFactories.asSequence() .mapNotNull { it.createUi(screen, themedContext, parent) } .firstOrNull() - Restore UI state if adequate - Bind UI to Presenter - newPresenterScope.launch { ui.setEventReceiver(presenter::sendEvent) presenter.models.collect(ui::setModel) } - Deliver results - Attach UI and runs transition - Remove old UI
120. App
121. ɹɹɹType ɹɹFlavorɹ Debug Release Internal internalDebug internalRelease Production productionDebug productionRelease App
122. ɹɹɹType ɹɹFlavorɹ Debug Release Internal Dev Alpha Production productionDebug Prod App
123. Process restart
124. Bug reporting
125. Variant implementation
126. Variant implementation
127. App
128. Content Container/Navigator Activity
129. Debug Drawer Content Debug View Container/Navigator Activity
130. Workers /** Arbitrary code that needs to run as the result of [MainActivity]'s creation. */ interface ActivityWorker { /** * Called during `MainActivity.onCreate`. Implementers may assume that [work] invocations are * never cancelled. */ suspend fun work(lifecycle: Lifecycle) } /** Arbitrary code that needs to run as the result of application creation. */ interface ApplicationWorker { /** * Called once during `Application.onCreate` to initialise this worker. To receive other * `Application` lifecycle events inject an `Observable<ApplicationEvent>` and react to its * emissions. * * Implementers may assume that [work] invocations will never be cancelled. */ suspend fun work() }
131. Development process • No feature branch. • Feature flag! • Small and stacked PRs. • PR Reviews? Trust by default. • Avoid bike-shedding with automation and lint. • Version bump are mostly automatic.
134. Dependency diff
135. Bundles diff
138. Android Test? • Just a very few. • Mock mode: no network dependency. • Runtime check.
139. Mobile Releases
140. Design System • Own Repo • Artifact for all platforms • Colors, Icons, Dimensions, Typography • Website to browse it! • Figma uses it • Tools to migrate
142. Design System
143. Design System
146. Text( modifier = Modifier.padding(vertical = 6.dp), text = "Good stuff", style = SecretTheme.typography.body, color = SecretTheme.colors.semantic.text.prominent, ) Design System
147. Functional Teams • Independent team / feature • PM/Design/Server/Mobile • Bottom-up! but… • Pros • Velocity • Cons • Conflict
148. Dynamic Feature
149. The Future
150. The Future Now
151. Open Source • All part of our tech stack. • Any can do it. • Part of the work.
152. Fin
153. References • Cash App Code Blog • https://code.cash.app/ • Square on Github • https://github.com/square • Cash App on Github • https://github.com/cashapp • Variants on steroids with Dagger • https://github.com/JakeWharton/u2020/ • Code that last forever • https://www.youtube.com/watch?v=YZstpc2939s • Debug builds • https://www.youtube.com/watch?v=Ae4vqz29W9U