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Mohit Sarveiya Building Shared UIs Across Platforms with Compose @heyitsmohit

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Building Shared UIs Across Platforms with Compose ● Setup & Architecture

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Building Shared UIs Across Platforms with Compose ● Setup & Architecture ● Internals

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Building Shared UIs Across Platforms with Compose ● Setup & Architecture ● Internals ● Interop with iOS

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Android Kotlin/JVM iOS Swift/LLVM Web JS Desktop Kotlin/JVM

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API Share Cache Business Logic Platforms

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API Share Cache Business Logic UI Components Platforms

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https: / / github.com/JetBrains/compose-multiplatform compose-multiplatform

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Approaches • Share all UI components Components (Compose)

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Approaches UI Components (Compose) • Share individual UI components UI Components (SwiftUI)

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Approaches UI Components (Compose) • Share individual UI components UI Components (SwiftUI) Shared Components (Compose)

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Approaches • Share individual UI components • Share all UI components

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Example • SwiftUI App • Display list of images

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Example • SwiftUI App • Display list of images • Details page

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Goal • Display list of images (Compose) • Details page (SwiftUI)

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Goal ZStack { LazyVGrid( ... ) { ForEach(id: .id) { item in Image(item.url) .renderingMode(.original) .resizable() .scaledToFill() } }.task { await repository.getImages() } }

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UI Structure Shared Component NavigationView { ZStack { ComposeView() } }.toolbar { ... }

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https: / / github.com/JetBrains/compose-multiplatform-template compose-multiplatform

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androidApp iOSApp shared Structure

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shared src commonMain androidMain iOSMain Shared Module

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shared src commonMain androidMain iOSMain build.gradle.kts Shared Module

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plugins { kotlin("multiplatform") } val commonMain by getting { dependencies { implementation(compose.ui) implementation(compose.foundation) implementation(compose.material) implementation(compose.runtime) } } Shared Module

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plugins { kotlin("multiplatform") } val commonMain by getting { dependencies { implementation(compose.ui) implementation(compose.foundation) implementation(compose.material) implementation(compose.runtime) } } Shared Module

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UI Structure

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UI Structure Shared Component NavigationView { ZStack { ComposeView() } }.toolbar { ... }

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UI Structure Compose View Images List ViewController AppTheme NavigationView { ZStack { ComposeView() } }.toolbar { ... }

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shared src commonMain androidMain iOSMain ImagesAppTheme.kt Shared Module

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App Theme

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App Theme val LightColorPalette = lightColors( ... ) val DarkColorPalette = darkColors( ... ) @Composable fun ImagesAppTheme( darkTheme: Boolean = isSystemInDarkTheme(), content: @Composable () -> Unit ) { MaterialTheme( colors = if (darkTheme) DarkColorPalette else LightColorPalette, content = content )

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App Theme @Composable fun ImagesAppTheme( darkTheme: Boolean = isSystemInDarkTheme(), content: @Composable () -> Unit ) { MaterialTheme( colors = if (darkTheme) DarkColorPalette else LightColorPalette, content = content ) }

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App Theme @Composable fun ImagesAppTheme( darkTheme: Boolean = isSystemInDarkTheme(), content: @Composable () -> Unit ) { MaterialTheme( colors = if (darkTheme) DarkColorPalette else LightColorPalette, content = content ) }

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UI Structure Compose View Images List ViewController AppTheme NavigationView { ZStack { ComposeView() } }.toolbar { ... }

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UI Structure struct ComposeView: UIViewControllerRepresentable { 
 func makeUIViewController(context: Context) -> UIViewController { let controller = Main_iosKt.MainiOS() return controller } }

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UI Structure struct ComposeView: UIViewControllerRepresentable { 
 func makeUIViewController( ... ) -> UIViewController { let controller = Main_iosKt.MainiOS() return controller } }

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UI Structure struct ComposeView: UIViewControllerRepresentable { 
 func makeUIViewController( ... ) -> UIViewController { let controller = ImagesList() return controller } }

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UI Structure fun ImagesList(): UIViewController = ComposeUIViewController { ImagesAppCommon() }

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UI Structure fun ImagesList(): UIViewController = ComposeUIViewController { ... }

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Compose Architecture Compose Multiplatform Compose Multiplatform Core

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https: / / github.com/JetBrains/compose-multiplatform-core compose-multiplatform

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Multiplatform Core fun ComposeUIViewController( content: @Composable () -> Unit ): UIViewController = ComposeWindow().apply { configuration = ComposeUIViewControllerConfiguration() .apply(configure) setContent(content) }

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Multiplatform Core fun ComposeUIViewController( content: @Composable () -> Unit ): UIViewController = ComposeWindow().apply { setContent(content) }

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UI Structure Compose View Images List ViewController AppTheme NavigationView { ZStack { ComposeView() } }.toolbar { ... }

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UI Structure fun ImagesList(): UIViewController = ComposeUIViewController { ... }

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UI Structure fun ImagesList(): UIViewController = ComposeUIViewController { AppTheme { 
 } } Text("Hello World")

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UI Structure struct ContentView: View { 
 var body: some View { ZStack { ComposeView() ...
 } } 
 } Hello World

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UI Structure UIWindowScene UIWindow ComposeWindow SkikkoUIView View Hierarchy struct ContentView: View { 
 var body: some View { ZStack { ComposeView() ...
 } } 
 } UIWindowScene UIWindow ComposeWindow SkikkoUIView

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UI Structure UIWindowScene UIWindow ComposeWindow SkikkoUIView View Hierarchy struct ContentView: View { 
 var body: some View { ZStack { ComposeView() ...
 } } 
 } UIWindowScene UIWindow ComposeWindow SkikkoUIView

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UI Structure UIWindowScene UIWindow ComposeWindow SkikkoUIView View Hierarchy struct ContentView: View { 
 var body: some View { ZStack { ComposeView() ...
 } } 
 } UIWindowScene UIWindow ComposeWindow SkikkoUIView

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https: / / github.com/JetBrains/skiko Skiko

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Compose Multiplatform Architecture Skia Skiko Compose UIViewController UIKit SwiftUI

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UI Structure UIWindowScene UIWindow ComposeWindow SkikkoUIView View Hierarchy struct ContentView: View { 
 var body: some View { ZStack { ComposeView() ...
 } } 
 } UIWindowScene UIWindow ComposeWindow SkikkoUIView

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UI Structure class ComposeWindow : UIViewController { var layer: ComposeLayer var content: @Composable () -> Unit 
 override fun loadView() { ... } }

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UI Structure fun ImagesList(): UIViewController = ComposeUIViewController { AppTheme { 
 } } Text("Hello World")

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Compose Multiplatform Architecture Skia Skiko Compose UIViewController UIKit SwiftUI

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UI Structure class ComposeWindow : UIViewController { override fun loadView() { val skiaLayer = createSkiaLayer() val skikoUIView = SkikoUIView(skiaLayer = skiaLayer).load() val rootView = UIView() rootView.addSubview(skikoUIView) } }

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UI Structure class ComposeWindow : UIViewController { override fun loadView() { val skiaLayer = createSkiaLayer() val skikoUIView = SkikoUIView(skiaLayer = skiaLayer).load() val rootView = UIView() rootView.addSubview(skikoUIView) layer = ComposeLayer(layer = skiaLayer) layer.setContent( CompositionLocalProvider( ... ) { content() } } ) } }

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UI Structure struct ContentView: View { 
 var body: some View { ZStack { ComposeView() ...
 } } 
 } Hello World

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Architecture

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UI Structure struct ContentView: View { 
 var body: some View { ZStack { ComposeView() ...
 } } 
 }

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Architecture View Repo View Model 
 SwiftUI ComposeView Shared

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View Model Repository View Request Response UI State Event

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https: / / github.com/cashapp/molecule Molecule

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@Composable fun Presenter(): Model State Flow Compose Runtime Recomposition

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@Composable fun Presenter(): Model State Flow Recomposition Monotomic Frame Clock

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Molecule Muiltiplatform Support ● Android (all versions) ● JS (0.3.0 and newer) ● JVM (0.3.0 and newer) ● iOS (0.5.0-beta01 and newer) ● MacOS (0.5.0-beta01 and newer)

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https: / / github.com/icerockdev/moko-mvvm Moko

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Architecture sealed class UiState { object Loading: UiState() data class Success( val images: List ): UiState() data class Error( val errorMessage: String ): UiState() }

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Architecture abstract class MoleculeViewModel <> : ViewModel() { }

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Architecture abstract class MoleculeViewModel: ViewModel() { }

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Architecture abstract class MoleculeViewModel: ViewModel() { }

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Architecture abstract class MoleculeViewModel: ViewModel() { val scope = CoroutineScope( viewModelScope.coroutineContext ) }

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Architecture Frame Clock DisplayLinkClock iOS AndroidUiFrameClock Android

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https: / / developer.apple.com/documentation/quartzcore/cadisplaylink CADisplayLink

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Architecture abstract class MoleculeViewModel: ViewModel() { val scope = CoroutineScope( viewModelScope.coroutineContext + DisplayLinkClock ) }

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Architecture object DisplayLinkClock : MonotonicFrameClock { val displayLink: CADisplayLink = val clock = BroadcastFrameClock { ... } override suspend fun withFrameNanos(onFrame: (frameTimeNanos: Long) -> R): R { return clock.withFrameNanos(onFrame) } }

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Architecture abstract class MoleculeViewModel: ViewModel() { val scope = CoroutineScope(…) val models: StateFlow by lazy(…) { scope.launchMolecule(mode = RecompositionMode.ContextClock) { models(…) } } }

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Architecture abstract class MoleculeViewModel: ViewModel() { val scope = CoroutineScope(…) val models: StateFlow by lazy(…) { scope.launchMolecule(mode = RecompositionMode.ContextClock) { models(…) } } }

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Architecture abstract class MoleculeViewModel: ViewModel() { val scope = CoroutineScope(…) val models: StateFlow by lazy(…) { scope.launchMolecule(mode = RecompositionMode.ContextClock) { models(…) } } }

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View Model View UI State Event

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Architecture abstract class MoleculeViewModel: ViewModel() { val events = MutableSharedFlow(extraBufferCapacity = 20) fun take(event: Event) { if (!events.tryEmit(event)) { error("Event buffer overflow.") } } }

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Architecture abstract class MoleculeViewModel: ViewModel() { val events = MutableSharedFlow(extraBufferCapacity = 20) fun take(event: Event) { if (!events.tryEmit(event)) { error("Event buffer overflow.") } } }

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Architecture View Repo View Model 
 SwiftUI ComposeView Shared

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Architecture class ImagesViewModel: MoleculeViewModel() { }

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Architecture class ImagesViewModel: MoleculeViewModel() { @Composable override fun models(events: Flow): UiState { } }

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Architecture @Composable override fun models(events: Flow): UiState { var uiState by remember { mutableStateOf(UIState.Loading) } }

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Architecture @Composable override fun models(events: Flow): UiState { var uiState by remember { mutableStateOf(UIState.Loading) } LaunchedEffect(Unit) { } }

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Architecture @Composable override fun models(events: Flow): UiState { var uiState by remember { mutableStateOf(UIState.Loading) } LaunchedEffect(Unit) { val imagesList = imagesRepository.getImages() uiState = UIState.Success(imagesList) } }

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Architecture @Composable override fun models(events: Flow): UiState { var uiState by remember { mutableStateOf(UIState.Loading) } LaunchedEffect(Unit) { val imagesList = imagesRepository.getImages() uiState = UIState.Success(imagesList) } return uiState }

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Architecture fun ImagesList(): UIViewController = ComposeUIViewController { AppTheme { 
 } }

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Architecture ComposeUIViewController { AppTheme { 
 val viewModel = getViewModel(…, viewModelFactory { ImagesViewModel() }) } }

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Architecture ComposeUIViewController { AppTheme { 
 val viewModel = getViewModel(…) val model by viewModel.models.collectAsState() } }

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Architecture ComposeUIViewController { AppTheme { 
 val viewModel = getViewModel(…) val model by viewModel.models.collectAsState() ImagesList(model) } }

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Architecture View Repo View Model 
 SwiftUI ComposeView Shared

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Architecture fun ImagesList(model: UiState) { Column { LazyVerticalGrid { items(images) { ... } } } }

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https: / / github.com/Kamel-Media/Kamel Kamel

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Architecture fun ImagesList(model: UiState) { Column { LazyVerticalGrid { items(images) { KamelImage( asyncPainterResource(image.path), contentScale = ContentScale.Crop, ) } }

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UI Structure struct ContentView: View { 
 var body: some View { ZStack { ComposeView() ...
 } } 
 }

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Architecture View Repo View Model 
 SwiftUI ComposeView Shared

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iOS Interop

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● Compose in SwiftUI Interop

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● Compose in SwiftUI ● SwiftUI in Compose Interop

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Interop View in Compose

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Interop SwiftUI View View in Compose

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Interop Compose View SwiftUI View Provide

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Interop shared src commonMain androidMain iOSMain App Screen

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Interop fun AppScreen(createUIView: () -> UIView): UIViewController = ComposeUIViewController { Column( horizontalAlignment = Alignment.CenterHorizontally ) { Text("How to use SwiftUI inside Compose") UIKitView( factory = createUIView, modifier = Modifier.size(300.dp).border(2.dp, Color.Blue), ) } }

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Interop fun AppScreen(createUIView: () -> UIView): UIViewController = ComposeUIViewController { Column( horizontalAlignment = Alignment.CenterHorizontally ) { Text("How to use SwiftUI inside Compose") UIKitView( factory = createUIView, modifier = Modifier.size(300.dp).border(2.dp, Color.Blue), ) } }

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Interop fun AppScreen(createUIView: () -> UIView): UIViewController = ComposeUIViewController { Column( horizontalAlignment = Alignment.CenterHorizontally ) { Text(“View in Compose”) UIKitView( factory = createUIView, modifier = Modifier.size(300.dp).border(2.dp, Color.Blue), ) } }

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Interop fun AppScreen(createUIView: () -> UIView): UIViewController = ComposeUIViewController { Column( horizontalAlignment = Alignment.CenterHorizontally ) { Text(“View in Compose”) UIKitView( factory = createUIView, modifier = Modifier.size(300.dp).border(2.dp, Color.Blue), ) } }

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Interop App Screen SwiftUI View Provide

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androidApp iOSApp desktopApp shared Interop

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Interop struct ComposeView: UIViewControllerRepresentable { 
 func makeUIViewController( ... ) -> UIViewController { AppScreen( VStack { Text(“Compose View”) } ) } }

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Interop struct ComposeView: UIViewControllerRepresentable { 
 func makeUIViewController( ... ) -> UIViewController { AppScreen( VStack { Text(“Compose View”) } ) } }

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Interop struct ComposeView: UIViewControllerRepresentable { 
 func makeUIViewController( ... ) -> UIViewController { AppScreen( VStack { Text(“SwiftUI in Compose”) } ) } } SwiftUI in Compose Compose View

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● Compose in SwiftUI ● SwiftUI in Compose ● UIKit in Compose Interop

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https: / / github.com/chrisbanes/tivi Tivi

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Problem ● Tivi App ● Modal in Compose

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Problem ● Tivi App ● Modal in Compose ● Show iOS date picker from Compose

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Interop shared src commonMain androidMain iOSMain Expect Declaration

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Interop shared src commonMain androidMain iOSMain Actual Declaration Actual Declaration

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Interop @Composable expect fun TimePickerDialog( onDismissRequest: () -> Unit, onTimeChanged: (LocalTime) -> Unit, selectedTime: LocalTime )

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Interop shared src commonMain androidMain iOSMain Actual Declaration

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Interop @Composable actual fun TimePickerDialog(…) { DatePickerViewController(backgroundColor).apply { ... confirmButton.setTitle(confirmLabel, UIControlStateNormal) } }

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Interop @Composable actual fun TimePickerDialog(…) { DatePickerViewController(backgroundColor).apply { ... confirmButton.setTitle(confirmLabel) } }

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Interop class DatePickerViewController( ... ) : UIViewController { }

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Interop class DatePickerViewController( ... ) : UIViewController { val datePicker = UIDatePicker() val stack = UIStackView() override fun viewDidLoad() { super.viewDidLoad() . .. view.addSubview(stack) } }

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Interop class DatePickerViewController( ... ) : UIViewController { val datePicker = UIDatePicker() val stack = UIStackView() override fun viewDidLoad() { super.viewDidLoad() . .. view.addSubview(stack) } }

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Interop shared src commonMain androidMain iOSMain Actual Declaration

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Interop @Composable actual fun TimePickerDialog(…) { }

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Interop @Composable actual fun TimePickerDialog(…) { androidx.compose.material3.DatePickerDialog(…) { TimePicker( state = timePickerState, modifier = Modifier .padding(top = 32.dp) .align(Alignment.CenterHorizontally), ) } }

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Problem ● Tivi App ● Modal in Compose ● Show iOS date picker from Compose

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● Compose in SwiftUI ● SwiftUI in Compose ● UIKit in Compose Interop

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No content

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Roadmap ● Navigation ● Transitions ● Text selection and input ● Accessibility ● Dialogs and popups

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Building Shared UIs Across Platforms with Compose ● Setup & Architecture ● Internals ● Interop with iOS

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Thank You! www.codingwithmohit.com @heyitsmohit