MVI with Jetpack Compose

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About me ● Luca ● Italian ● Android Engineer @Babylon Health ● Based in London @luca_nicolett

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MVI Jetpack Compose Topics

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MVI

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MVI MODEL INTENT VIEW USER Updates Sees Manipulates Interacts

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MVI Core principles: ● Unidirectional ● Immutability ● Reactiveness ● Functional

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MVI

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MVI ACTIONS BUSINESS LOGIC EVENTS REDUCER STATE STATE UI LISTENS UI

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MVI ACTIONS ACTION RELAY TRANSFORMERS REDUCER STATE UPDATES SOMETHING ACTIONS EVENTS STATE STATE RELAY

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MVI ● Actions ● Transformers ● Reducers ● State

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MVI We also added middleware ● Works as a glue ● Binds actions to transformers ● Transformations to reducers ● Or actions to reducers directly

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MVI perform("rating selection") .on() .withReducer(reducers::reduceRatingSelected)

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MVI perform("load logged in patient data") .on( LifecycleAction.Created::class.java, ProfileScreenAction.RetryConnection::class.java, ProfileScreenAction.MonitorReady::class.java ) .transform { transformers.loadPatient(this) } .withReducer(reducers::reduceLoggedInPatient)

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MVI perform("load logged in patient") .on( LifecycleAction.Created::class.java, ProfileScreenAction.RetryConnection::class.java, ProfileScreenAction.MonitorReady::class.java ) .transform { transformers.loadPatient(this) } .withReducer(reducers::reduceLoggedInPatient)

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MVI How does it help? ● Decoupling ● Testing

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MVI

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MVI

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MVI ACTIVITY FRAGMENT render() RENDERER

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MVI private fun render(state: HomeScreenRedesignState) { loading_container .show(state.loadingState == LoadingState.Loading) unable_to_connect_error_container .show(state.loadingState == LoadingState.Error) /* ... */ }

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MVI fun View.show(isVisible: Boolean = true) { this.visibility = if (isVisible) View.VISIBLE else View.GONE }

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MVI private fun render(state: EditMoodState) { submitEditsButton?.isEnabled = state.hasAppliedChanges /* ... */ }

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MVI private fun render(state: AddMoodState) { if (state.showUrgentHelpDialog) { showUrgentHelpDialog() return } /* ... */ }

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MVI

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Jetpack Compose

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Jetpack Compose

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Jetpack Compose

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Jetpack Compose ● Declarative UI ● Concise and idiomatic ● Stateless or Stateful components ● Reusable components ● Compatible

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Jetpack Compose @Composable @GenerateView fun Greetings(name: String) { /* ... */ } val greetingsView = findViewById(R.id.greetings) greetingsView.name = "Luca"

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Jetpack Compose @Composable @GenerateView fun Greetings(name: String) { /* ... */ } val greetingsView = findViewById(R.id.greetings) greetingsView.name = "Luca"

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Jetpack Compose @Composable @GenerateView fun Greetings(name: String) { /* ... */ } val greetingsView = findViewById(R.id.greetings) greetingsView.name = "Luca"

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Jetpack Compose ● Declarative UI ● Concise and idiomatic ● Stateless or Stateful components ● Reusable components ● Compatible ● Unbundled from OS

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Jetpack Compose

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mkdir ~/bin PATH=~/bin:$PATH curl https://storage.googleapis.com/git-repo-downloads/repo > ~/bin/repo chmod a+x ~/bin/repo Jetpack Compose

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Jetpack Compose mkdir androidx-master-dev cd androidx-master-dev repo init -u https://android.googlesource.com/platform/manifest -b androidx-master-dev repo sync -j8 -c

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Jetpack Compose mkdir androidx-master-dev cd androidx-master-dev repo init -u https://android.googlesource.com/platform/manifest -b androidx-master-dev repo sync -j8 -c Download the code (and grab a coffee while we pull down 6GB)

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cd path/to/checkout/frameworks/support/ ./studiow Jetpack Compose

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Jetpack Compose

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class MyActivity: Activity() { override fun onCreate(savedInstanceState: Bundle?) { super.onCreate(savedInstanceState) setContent { MyComposableFunction() } } } Jetpack Compose

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fun Activity.setContent(content: @Composable() () -> Unit) : CompositionContext? { /* ... */ } Jetpack Compose

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fun Activity.setContent(content: @Composable() () -> Unit) : CompositionContext? { /* ... */ } Jetpack Compose

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val craneView = window.decorView .findViewById(android.R.id.content) .getChildAt(0) as? AndroidCraneView ?: AndroidCraneView(this).also { setContentView(it) } Jetpack Compose

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val coroutineContext = Dispatchers.Main return Compose.composeInto(craneView.root, this) { WrapWithAmbients(craneView, this, coroutineContext) { content() } } Jetpack Compose

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@Composable fun Greetings(name: String) { Text("Hello $name") } Jetpack Compose

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@Composable fun Text(/* ... */) { /* ... */ Draw { canvas, _ -> internalSelection.value?.let { textDelegate.paintBackground( it.min, it.max, selectionColor, canvas ) } textDelegate.paint(canvas) } /* ... */ } Jetpack Compose

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Jetpack Compose

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Jetpack Compose

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@Composable fun TextField(/* ... */) { // States val hasFocus = +state { false } val coords = +state { null } /* ... */ } Jetpack Compose

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@CheckResult("+") /* inline */ fun state(init: () -> T) = memo { State(init()) } Jetpack Compose

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/** * The State class is an @Model class meant to * wrap around a single value. * It is used in the `+state` and `+stateFor` effects. */ @Model class State @PublishedApi internal constructor(value:T) : Framed { /* ... */ } Jetpack Compose

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/** * [Model] can be applied to a class which represents your * application's data model, and will cause instances of the * class to become observable, such that a read of a property * of an instance of this class during the invocation of a * composable function will cause that component to be * "subscribed" to mutations of that instance. Composable * functions which directly or indirectly read properties of the * model class, the composables will be recomposed whenever any * properties of the the model are written to. */ Jetpack Compose

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@Model data class TaskModel( var isDone: Boolean, val description: String ) Jetpack Compose

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@Model data class TaskModel( var isDone: Boolean, val description: String ): BaseModel() Jetpack Compose

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@Model data class TaskModel( var isDone: Boolean, val description: String ): BaseModel() TaskModel.kt: (14, 3): Model objects do not support inheritance Jetpack Compose

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@Composable fun RallyBody() { Padding(padding = 16.dp) { Column { // TODO: scrolling container RallyAlertCard() HeightSpacer(height = 10.dp) RallyAccountsCard() } } } Jetpack Compose

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@Composable fun RallyBody() { Padding(padding = 16.dp) { VerticalScroller { Column { RallyAlertCard() HeightSpacer(height = 10.dp) RallyAccountsCard() } } } } Jetpack Compose

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Jetpack Compose

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Jetpack Compose

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@Composable fun DrawSeekBar(x: Float) { var paint = +memo { Paint() } Draw { canvas, parentSize -> /* ... */ canvas.drawRect(Rect(/* ... */), paint) canvas.drawRect(Rect(/* ... */), paint) canvas.drawCircle(/* ... */, paint) } } Jetpack Compose

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Jetpack Compose

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Text(text = "Row") ContainerWithBackground( width = ExampleSize, color = lightGrey ) { Row { PurpleSquare() CyanSquare() } } Jetpack Compose

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Jetpack Compose ContainerWithBackground( width = ExampleSize, color = lightGrey ) { Row( mainAxisAlignment = MainAxisAlignment.End ) { PurpleSquare() CyanSquare() } }

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Text(text = "Column") ContainerWithBackground( height = ExampleSize, color = lightGrey ) { Row { Column { PurpleSquare() CyanSquare() } /* ... */ } } Jetpack Compose

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Jetpack Compose ContainerWithBackground( height = ExampleSize, color = lightGrey ) { Column( crossAxisAlignment = CrossAxisAlignment.End ) { PurpleSquare() CyanSquare() } }

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Jetpack Compose

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@Composable fun RippleRect() { val toState = +state{ ButtonStatus.Initial } val onPress:(PxPosition) -> Unit = { p -> down.x = p.x.value down.y = p.y.value toState.value = ButtonStatus.Pressed } /* ... */ } Jetpack Compose

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@Composable fun RippleRect() { /* ... */ val onRelease: () -> Unit = { toState.value = ButtonStatus.Released } /* ... */ } Jetpack Compose

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PressGestureDetector(onPress, onRelease) { Container(expanded = true) { Transition(toState = toState.value) { s-> RippleRectFromState(s) } } } Jetpack Compose

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@Composable fun RippleRectFromState(state: TransitionState) { Draw { canvas, _ -> canvas.drawCircle( Offset(x, y), radius, paint ) } } Jetpack Compose

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Jetpack Compose

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@Composable fun AlertDialog( onCloseRequest: () -> Unit, title: (@Composable() () -> Unit), text: (@Composable() () -> Unit), confirmButton: (@Composable() () -> Unit), dismissButton: (@Composable() () -> Unit), buttonLayout: AlertDialogButtonLayout ) { /* ... */ } Jetpack Compose

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Jetpack Compose @Composable fun Dialog( onCloseRequest: () -> Unit, children: @Composable() () -> Unit ) { val context = +ambient(ContextAmbient) val dialog = +memo { DialogWrapper(context, onCloseRequest) } }

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Jetpack Compose @Composable fun Dialog( onCloseRequest: () -> Unit, children: @Composable() () -> Unit ) { +onActive { dialog.show() onDispose { dialog.dismiss() dialog.disposeComposition() } } }

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Jetpack Compose @Composable fun Dialog( onCloseRequest: () -> Unit, children: @Composable() () -> Unit ) { +onCommit { dialog.setContent(children) } }

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@RunWith(JUnit4::class) @get:Rule val composeTestRule = createComposeRule() Jetpack Compose

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Jetpack Compose @Test fun topAppBar_expandsToScreen() { val dm = composeTestRule.displayMetrics composeTestRule .setMaterialContentAndCollectSizes { TopAppBar() } .assertHeightEqualsTo(appBarHeight) .assertWidthEqualsTo { dm.widthPixels.ipx } }

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All together

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All together Functional approach OOP approach

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All together interface BaseViewState { @Composable fun buildUI() }

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All together object InProgress : BaseViewState(true, null) { @Composable override fun buildUI() { Container(expanded = true) { CircularProgressIndicator() } } }

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override fun onCreate(savedInstanceState: Bundle?) { super.onCreate(savedInstanceState) viewModel = /* view model init */ setContent { CustomTheme { render(viewModel.states()) } } /* .. */ } All together

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override fun render( observableState: Observable ) { val state = +observe(ViewState.Idle, observableState) state.buildUI() } All together

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override fun render( observableState: Observable ) { val state = +observe(ViewState.Idle, observableState) state.buildUI() } All together

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override fun render( observableState: Observable ) { val state = +observe(ViewState.Idle, observableState) state.buildUI() } All together

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fun observe(initialState: T, data: Observable) = effectOf { val result = +state { initialState } +onActive { val disposable = data.subscribe { newValue -> result.value = newValue } onDispose { disposable.dispose() } } return result.value } All together

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All together override fun onCreate(savedInstanceState: Bundle?) { super.onCreate(savedInstanceState) // viewModel = /* ... */ not needed anymore setContent { PostListScreen( processIntents(intents()), reloadPostListIntentPublisher ) } }

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All together fun processIntents(intents: Observable): PostListViewState { intents.subscribe(intentsObserver) return modelState() } }

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All together fun modelState() = +effectOf { val result = +state { PostListViewState.Idle } var disposable: Disposable? = null +onActive { /* ... */ } +onDispose { disposable?.dispose() } result.value }

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All together +onActive { disposable = intentsObserver .applyBusinessLogic() .subscribe { result.value = it } }

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All together @Composable fun PostListScreen( state: PostListViewState ) { when (state) { PostListViewState.InProgress -> { /* ... */ } } }

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All together PostListScreen(processIntents(intents()))

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All together

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All together PostListScreen( processIntents( intents() ) )

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References MVI http://hannesdorfmann.com/android/model-view-intent https://www.novatec-gmbh.de/en/blog/mvi-in-android/ https://cycle.js.org/model-view-intent.html Jetpack https://www.youtube.com/watch?v=VsStyq4Lzxo https://medium.com/q42-engineering/android-jetpack-compose-895b7fd04bf4 https://blog.karumi.com/android-jetpack-compose-review/