compose-multiplatform-patterns

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Compose Multiplatform Patterns

Patterns for building shared UI across Android, iOS, Desktop, and Web using Compose Multiplatform and Jetpack Compose. Covers state management, navigation, theming, and performance.

When to Activate

Building Compose UI (Jetpack Compose or Compose Multiplatform)
Managing UI state with ViewModels and Compose state
Implementing navigation in KMP or Android projects
Designing reusable composables and design systems
Optimizing recomposition and rendering performance

State Management

ViewModel + Single State Object

Use a single data class for screen state. Expose it as StateFlow and collect in Compose:

kotlin

data class ItemListState(
    val items: List<Item> = emptyList(),
    val isLoading: Boolean = false,
    val error: String? = null,
    val searchQuery: String = ""
)

class ItemListViewModel(
    private val getItems: GetItemsUseCase
) : ViewModel() {
    private val _state = MutableStateFlow(ItemListState())
    val state: StateFlow<ItemListState> = _state.asStateFlow()

    fun onSearch(query: String) {
        _state.update { it.copy(searchQuery = query) }
        loadItems(query)
    }

    private fun loadItems(query: String) {
        viewModelScope.launch {
            _state.update { it.copy(isLoading = true) }
            getItems(query).fold(
                onSuccess = { items -> _state.update { it.copy(items = items, isLoading = false) } },
                onFailure = { e -> _state.update { it.copy(error = e.message, isLoading = false) } }
            )
        }
    }
}

Collecting State in Compose

kotlin

@Composable
fun ItemListScreen(viewModel: ItemListViewModel = koinViewModel()) {
    val state by viewModel.state.collectAsStateWithLifecycle()

    ItemListContent(
        state = state,
        onSearch = viewModel::onSearch
    )
}

@Composable
private fun ItemListContent(
    state: ItemListState,
    onSearch: (String) -> Unit
) {
    // Stateless composable — easy to preview and test
}

Event Sink Pattern

For complex screens, use a sealed interface for events instead of multiple callback lambdas:

kotlin

sealed interface ItemListEvent {
    data class Search(val query: String) : ItemListEvent
    data class Delete(val itemId: String) : ItemListEvent
    data object Refresh : ItemListEvent
}

// In ViewModel
fun onEvent(event: ItemListEvent) {
    when (event) {
        is ItemListEvent.Search -> onSearch(event.query)
        is ItemListEvent.Delete -> deleteItem(event.itemId)
        is ItemListEvent.Refresh -> loadItems(_state.value.searchQuery)
    }
}

// In Composable — single lambda instead of many
ItemListContent(
    state = state,
    onEvent = viewModel::onEvent
)

Navigation

Type-Safe Navigation (Compose Navigation 2.8+)

Define routes as @Serializable objects:

kotlin

@Serializable data object HomeRoute
@Serializable data class DetailRoute(val id: String)
@Serializable data object SettingsRoute

@Composable
fun AppNavHost(navController: NavHostController = rememberNavController()) {
    NavHost(navController, startDestination = HomeRoute) {
        composable<HomeRoute> {
            HomeScreen(onNavigateToDetail = { id -> navController.navigate(DetailRoute(id)) })
        }
        composable<DetailRoute> { backStackEntry ->
            val route = backStackEntry.toRoute<DetailRoute>()
            DetailScreen(id = route.id)
        }
        composable<SettingsRoute> { SettingsScreen() }
    }
}

Dialog and Bottom Sheet Navigation

Use dialog() and overlay patterns instead of imperative show/hide:

kotlin

NavHost(navController, startDestination = HomeRoute) {
    composable<HomeRoute> { /* ... */ }
    dialog<ConfirmDeleteRoute> { backStackEntry ->
        val route = backStackEntry.toRoute<ConfirmDeleteRoute>()
        ConfirmDeleteDialog(
            itemId = route.itemId,
            onConfirm = { navController.popBackStack() },
            onDismiss = { navController.popBackStack() }
        )
    }
}

Composable Design

Slot-Based APIs

Design composables with slot parameters for flexibility:

kotlin

@Composable
fun AppCard(
    modifier: Modifier = Modifier,
    header: @Composable () -> Unit = {},
    content: @Composable ColumnScope.() -> Unit,
    actions: @Composable RowScope.() -> Unit = {}
) {
    Card(modifier = modifier) {
        Column {
            header()
            Column(content = content)
            Row(horizontalArrangement = Arrangement.End, content = actions)
        }
    }
}

Modifier Ordering

Modifier order matters — apply in this sequence:

kotlin

Text(
    text = "Hello",
    modifier = Modifier
        .padding(16.dp)          // 1. Layout (padding, size)
        .clip(RoundedCornerShape(8.dp))  // 2. Shape
        .background(Color.White) // 3. Drawing (background, border)
        .clickable { }           // 4. Interaction
)

KMP Platform-Specific UI

expect/actual for Platform Composables

kotlin

// commonMain
@Composable
expect fun PlatformStatusBar(darkIcons: Boolean)

// androidMain
@Composable
actual fun PlatformStatusBar(darkIcons: Boolean) {
    val systemUiController = rememberSystemUiController()
    SideEffect { systemUiController.setStatusBarColor(Color.Transparent, darkIcons) }
}

// iosMain
@Composable
actual fun PlatformStatusBar(darkIcons: Boolean) {
    // iOS handles this via UIKit interop or Info.plist
}

Performance

Stable Types for Skippable Recomposition

Mark classes as @Stable or @Immutable when all properties are stable:

kotlin

@Immutable
data class ItemUiModel(
    val id: String,
    val title: String,
    val description: String,
    val progress: Float
)

Use `key()` and Lazy Lists Correctly

kotlin

LazyColumn {
    items(
        items = items,
        key = { it.id }  // Stable keys enable item reuse and animations
    ) { item ->
        ItemRow(item = item)
    }
}

Defer Reads with `derivedStateOf`

kotlin

val listState = rememberLazyListState()
val showScrollToTop by remember {
    derivedStateOf { listState.firstVisibleItemIndex > 5 }
}

Avoid Allocations in Recomposition

kotlin

// BAD — new lambda and list every recomposition
items.filter { it.isActive }.forEach { ActiveItem(it, onClick = { handle(it) }) }

// GOOD — key each item so callbacks stay attached to the right row
val activeItems = remember(items) { items.filter { it.isActive } }
activeItems.forEach { item ->
    key(item.id) {
        ActiveItem(item, onClick = { handle(item) })
    }
}

Theming

Material 3 Dynamic Theming

kotlin

@Composable
fun AppTheme(
    darkTheme: Boolean = isSystemInDarkTheme(),
    dynamicColor: Boolean = true,
    content: @Composable () -> Unit
) {
    val colorScheme = when {
        dynamicColor && Build.VERSION.SDK_INT >= Build.VERSION_CODES.S -> {
            if (darkTheme) dynamicDarkColorScheme(LocalContext.current)
            else dynamicLightColorScheme(LocalContext.current)
        }
        darkTheme -> darkColorScheme()
        else -> lightColorScheme()
    }

    MaterialTheme(colorScheme = colorScheme, content = content)
}

Anti-Patterns to Avoid

Using mutableStateOf in ViewModels when MutableStateFlow with collectAsStateWithLifecycle is safer for lifecycle
Passing NavController deep into composables — pass lambda callbacks instead
Heavy computation inside @Composable functions — move to ViewModel or remember {}
Using LaunchedEffect(Unit) as a substitute for ViewModel init — it re-runs on configuration change in some setups
Creating new object instances in composable parameters — causes unnecessary recomposition

References

See skill: android-clean-architecture for module structure and layering. See skill: kotlin-coroutines-flows for coroutine and Flow patterns.