36･15 Cash App

Mobile Dev Week at Abu Dhabi
----------------------
1400 modules. 60 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
5. Cash App • 60~ developpers • 1_500~ modules • 1_500_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. • Service • Manager • Syncer • Repository Backend • Reactive • Interface • real • fake
20. 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") suspend fun getCustomerSettings( @Body request: GetCustomerSettingsRequest, ): ApiResult<GetCustomerSettingsResponse> } Backend
21. 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") suspend fun getCustomerSettings( @Body request: GetCustomerSettingsRequest, ): ApiResult<GetCustomerSettingsResponse> } Backend
22. 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") suspend fun getCustomerSettings( @Body request: GetCustomerSettingsRequest, ): ApiResult<GetCustomerSettingsResponse> } Backend
23. 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
24. interface InvestmentEntities { fun discoveryStocks(forSearch: Boolean): Flow<DiscoverySections> fun stockDetails(token: InvestmentEntityToken): Flow<StockDetails> } Backend
25. 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 = forSearch) .asFlow() .mapToList(ioDispatcher) .f l atMapLatest { entities -> Backend
26. 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
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. interface Presenter<UiModel : Any, UiEvent : Any> { } Presenter
35. interface Presenter<UiModel : Any, UiEvent : Any> { val models: StateFlow<UiModel> fun sendEvent(event: UiEvent) } Presenter
36. interface Presenter<UiModel : Any, UiEvent : Any> { fun start( scope: CoroutineScope, ): Binding<UiModel, UiEvent> interface Binding<UiModel : Any, UiEvent : Any> { val models: StateFlow<UiModel> fun sendEvent(event: UiEvent) } } Presenter
37. interface MoleculePresenter<UiModel : Any, UiEvent : Any> { @Composable fun models( events: Flow<UiEvent>, ): UiModel } Presenter
38. 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], ) } }
39. 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], ) } }
40. 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], ) } }
41. Molecule
42. @Composable fun profilePresenter(userFlow, balanceFlow): profileModel {} val flow: Flow<ProfileModel> = moleculeFlow(Immediate) { profilePresenter(userFlow, balanceFlow) } val stateFlow: StateFlow<ProfileModel> = scope.launchMolecule(Immediate) { profilePresenter(userFlow, balanceFlow) } Molecule
43. fun interface EventReceiver<UiEvent> { fun sendEvent(event: UiEvent) } interface Ui<UiModel, UiEvent> { fun setEventReceiver(receiver: EventReceiver<UiEvent>) fun setModel(model: UiModel) } View
44. class ComposeUi<UiModel, UiEvent>( val content: @Composable ( model: UiModel, onEvent: (UiEvent) -> Unit) -> Unit, ) : ScreenUi View
45. ComposeUi { model, event -> CompositionLocalProvider( LocalImageLoader provides imageLoader, ) { @Composable fun HomeView( model: HomeViewModel, onEvent: (HomeViewEvent) -> Unit, ) { // ... } } } View
46. Protobuf Backend DB Network Presenter View Testing
47. Protobuf Backend DB Network Presenter View Testing
48. Testing
49. @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
50. @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
51. @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
52. Testing interface Navigator { fun goTo(screen: Screen) }
53. class FakeNavigator internal constructor() : Navigator { private val navigatedScreens = Turbine<Screen>() override fun goTo(screen: Screen) { navigatedScreens.add(screen) } suspend fun awaitNextScreen() = navigatedScreens.awaitItem() } Testing interface Navigator { fun goTo(screen: Screen) }
54. class DependentWelcomePresenterTest { @get:Rule val navigatorRule = FakeNavigatorRule() private val navigator = navigatorRule.navigator private val presenter = DependentWelcomePresenter( stringManager = TestStringManager(), navigator = navigator, ) @Test fun `button clicks navigates`() = runTest { presenter.test { skipItem("Initial model") Testing
55. class DependentWelcomePresenterTest { @get:Rule val navigatorRule = FakeNavigatorRule() private val navigator = navigatorRule.navigator private val presenter = DependentWelcomePresenter( stringManager = TestStringManager(), navigator = navigator, ) @Test fun `button clicks navigates`() = runTest { presenter.test { skipItem("Initial model") sendEvent(ButtonClicked) assertThat(navigator.awaitNextScreen()).isEqualTo(expected) } }
56. class DependentWelcomePresenterTest { @get:Rule val navigatorRule = FakeNavigatorRule() private val navigator = navigatorRule.navigator private val presenter = DependentWelcomePresenter( stringManager = TestStringManager(), navigator = navigator, ) @Test fun `button clicks navigates`() = runTest { presenter.test { skipItem("Initial model") sendEvent(ButtonClicked) assertThat(navigator.awaitNextScreen()).isEqualTo(expected) } }
57. Ui Testing
58. Ui Testing
59. class HomeViewTest() { @get:Rule val paparazzi = Paparazzi( theme = "Theme.Cash.Default", deviceConfig = DeviceConfig.PIXEL_4, ) @Test fun happy() { paparazzi.snapshot { CompositionLocalProvider( LocalImageLoader provides rememberPreviewImageLoader { this }, content = { HomeView(model = HomeViewModel(), onEvent = {}) }, ) } } } Ui Testing
60. Ui Testing
61. class HomeViewTest() { @get:Rule val paparazzi = Paparazzi( theme = "Theme.Cash.Default", deviceConfig = DeviceConfig.PIXEL_4, ) @Test fun happy() { paparazzi.snapshot { CompositionLocalProvider( LocalImageLoader provides rememberPreviewImageLoader { this }, content = { HomeView(model = HomeViewModel(), onEvent = {}) }, ) } } } Ui Testing
62. @Burst class HomeViewTest( private val nightMode: NightMode, accessibilityTextSize: AccessibilityTextSize, ) { @get:Rule val paparazzi = Paparazzi( theme = "Theme.Cash.Default", deviceConfig = DeviceConfig.PIXEL_4.copy( fontScale = accessibilityTextSize.scale, nightMode = nightMode, ), ) @Test fun happy() { paparazzi.snapshot { CompositionLocalProvider( LocalImageLoader provides rememberPreviewImageLoader { this }, content = { Ui Testing
63. @Burst class HomeViewTest( private val nightMode: NightMode, accessibilityTextSize: AccessibilityTextSize, ) { @get:Rule val paparazzi = Paparazzi( theme = "Theme.Cash.Default", deviceConfig = DeviceConfig.PIXEL_4.copy( fontScale = accessibilityTextSize.scale, nightMode = nightMode, ), ) @Test fun happy() { paparazzi.snapshot { CompositionLocalProvider( LocalImageLoader provides rememberPreviewImageLoader { this }, content = { Ui Testing
64. enum class com.android.resources.NightMode { NOTNIGHT, NIGHT, } enum class AccessibilityTextSize(val scale: Float) { DEFAULT(scale = 1f), LARGE(scale = 2f), } @Burst class HomeViewTest( private val nightMode: NightMode, accessibilityTextSize: AccessibilityTextSize, ) { @get:Rule val paparazzi = Paparazzi( theme = "Theme.Cash.Default", Ui Testing
65. enum class com.android.resources.NightMode { NOTNIGHT, NIGHT, } enum class AccessibilityTextSize(val scale: Float) { DEFAULT(scale = 1f), LARGE(scale = 2f), } @Burst class HomeViewTest( private val nightMode: NightMode, accessibilityTextSize: AccessibilityTextSize, ) { @get:Rule val paparazzi = Paparazzi( theme = "Theme.Cash.Default", Ui Testing NOTNIGHT DEFAULT NOTNIGHT LARGE NIGHT DEFAULT NIGHT LARGE
66. enum class com.android.resources.NightMode { NOTNIGHT, NIGHT, } enum class AccessibilityTextSize(val scale: Float) { DEFAULT(scale = 1f), LARGE(scale = 2f), } @Burst class HomeViewTest( private val nightMode: NightMode, accessibilityTextSize: AccessibilityTextSize, ) { @get:Rule val paparazzi = Paparazzi( theme = "Theme.Cash.Default", Ui Testing
67. Ui Testing
68. - Write tests. Ui Testing
69. - Write tests. - Record snapshots: ./gradlew module:recordPaparazziDebug Ui Testing
70. - Write tests. - Record snapshots: ./gradlew module:recordPaparazziDebug - Check snapshots into the repository. Ui Testing
71. - Write tests. - Record snapshots: ./gradlew module:recordPaparazziDebug - Check snapshots into the repository. - Run verify task on CI: ./gradlew module:verifyPaparazziDebug Ui Testing
79. Navigation
80. interface Screen : Parcelable Navigation
81. interface Screen : Parcelable @Parcelize data class StockDetails( val entityToken: EntityToken, ) : Screen Navigation
82. interface Navigator { fun goTo(screen: Screen) } Navigation
83. interface Navigator { fun goTo(screen: Screen) } LaunchedE f fect(events) { events.collect { event -> when (event) { ButtonClicked -> { // Start flow. } Close -> { // Navigate. } } } } Navigation
84. interface Navigator { fun goTo(screen: Screen) } LaunchedE f fect(events) { events.collect { event -> when (event) { ButtonClicked -> { // Start flow. } Close -> { navigator.goTo(SomeScreen()) } } } } Navigation
85. interface UiFactory { fun createUi( screen: Screen, context: Context, parent: ViewGroup, ): ScreenUi? } interface PresenterFactory { fun create( screen: Screen, navigator: Navigator, ): Presenter<*, *>? } interface TransitionFactory { fun createTransition( fromScreen: Screen, fromView: View, toScreen: Screen, toView: View, parent: ViewGroup, ): Animator? }
86. interface UiFactory { fun createUi( screen: Screen, context: Context, parent: ViewGroup, ): ScreenUi? }
87. class InvestingUiFactory @Inject internal constructor( private val customOrder: InvestingCustomOrderView.Factory, private val featureFlag: FeatureFlagManager, ) : UiFactory { override fun createUi(screen: Screen, context: Context, parent: ViewGroup): ScreenUi? { val view = when (screen) { is DependentWelcomeScreen -> return ComposeUi { /***/ } is CustomOrderScreen -> customOrder.build(context) is NotificationSettings -> if (featureFlag.newSettingsEnabled()) { return ComposeUi { InvestingNotificationSettingsNew() } } else { InvestingNotificationSettingsLegacy(context) } else -> XmlFactory.inflate( context = context, layoutResId = when (screen) { is InvestingHome -> R.layout.investing_home else -> return null }, parent = parent, ) } return ScreenUi.ViewUi(view)
88. class InvestingPresenterFactory @Inject internal constructor( private val notificationSettingsPresenter: InvestingNotificationSettingsPresenter.Factory, private val dependentWelcomePresenter: DependentWelcomePresenter.Factory, ) : PresenterFactory { override fun create( screen: Screen, navigator: Navigator, ): Presenter<*, *>? { return when (screen) { is DependentWelcomeScreen -> dependentWelcomePresenter .create(navigator) .asPresenter() is NotificationSettings -> notificationSettingsPresenter .create(screen, navigator) .asPresenter() else -> null } } }
89. fun MoleculePresenter<UiEvent, UiModel>.asPresenter() : Presenter<UiModel, UiEvent> { return object : Presenter<UiModel, UiEvent> { override fun start( scope: CoroutineScope, ): Presenter.Binding<UiModel, UiEvent> { // Wrap the Molecule presenter and bind // its lifecycle to `scope`. } } }
90. class Broadway( private val uiFactories: List<UiFactory> = listOf(), private val transitionFactories: List<TransitionFactory> = listOf(), private val presenterFactories: List<PresenterFactory> = listOf(), ) { fun createUiOrNull(...): ScreenUi? { return uiFactories.asSequence().mapNotNull { it.createUi(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() } }
91. 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) } }
92. - navigator.goTo(SomeScreen)
93. - navigator.goTo(SomeScreen) - Determine the screen type: full, overlay, meta.
94. - navigator.goTo(SomeScreen) - Determine the screen type: full, overlay, meta. - Back stack management
95. - navigator.goTo(SomeScreen) - Determine the screen type: full, overlay, meta. - Back stack management - Tear down old presenter
96. - navigator.goTo(SomeScreen) - Determine the screen type: full, overlay, meta. - Back stack management - Tear down old presenter - currentPresenterScope.cancel()
97. - navigator.goTo(SomeScreen) - Determine the screen type: full, overlay, meta. - Back stack management - Tear down old presenter - currentPresenterScope.cancel() - Save UI state
98. - 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
99. - 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()
100. - 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)
101. - 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
102. - 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()
103. - 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
104. - 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
105. - 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) }
106. - 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
107. - 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
108. - 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
109. App
110. ɹɹɹType ɹɹFlavorɹ Debug Release Internal internalDebug internalRelease Production productionDebug productionRelease App
111. ɹɹɹType ɹɹFlavorɹ Debug Release Internal Dev Alpha Production productionDebug Prod App
112. ɹɹɹType ɹɹFlavorɹ Debug Release Internal Dev continuous Alpha daily Production productionDebug Prod weekly App
115. Process restart
116. Bug reporting
117. Variant implementation - DI
118. Variant implementation - DI
119. Variant implementation - DI
120. App
121. Content Container/Navigator Activity
122. Debug Drawer Content Debug View Container/Navigator Activity
123. 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() }
124. Development process
125. Development process • Weekly branch cut.
126. Development process • Weekly branch cut. • No feature branch. • Feature flag!
127. Development process • Weekly branch cut. • No feature branch. • Feature flag! • Small and stacked PRs. • PR Reviews? Trust by default.
128. Development process • Weekly branch cut. • No feature branch. • Feature flag! • Small and stacked PRs. • PR Reviews? Trust by default. • Avoid bike-shedding with automation and lint.
129. Development process • Weekly branch cut. • No feature branch. • Feature flag! • Small and stacked PRs. • PR Reviews? Trust by default. • Avoid bike-shedding with automation and lint. • Dependency bumps are mostly automatic.
132. Dependency diff
133. Bundles diff
135. Android Test? • Just a very few. • Mock mode: no network dependency. • Runtime check.
136. Mobile Releases
137. Design System • Own Repo • Artifact for all platforms • Colors, Icons, Dimensions, Typography • Website to browse it! • Figma consumes it
138. Text( modifier = Modifier.padding(vertical = 6.dp), text = "Good stuff", style = CashTheme.typography.body, color = CashTheme.colors.semantic.text.prominent, ) Design System
140. Design System
141. Design System
144. Functional Teams • Independent team / feature • PM/Design/Server/Mobile • Bottom-up! but… • Pros • Velocity • Cons • Conflict
145. Open Source • As much as possible from our tech stack. • Any can do it. • Part of the work.
146. Fin
147. References • Cash App Code Blog • https://code.cash.app/ • Square on Github • https://github.com/square • Cash App on Github • https://github.com/cashapp