feat: add Kotlin, Android, and KMP rules, agent, skills, and command

2026-04-02 15:13:28 +08:00 · 2026-03-06 23:01:39 +01:00
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+---
+name: compose-multiplatform-patterns
+description: Compose Multiplatform and Jetpack Compose patterns for KMP projects — state management, navigation, theming, performance, and platform-specific UI.
+origin: ECC
+---
+
+# 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()
+    }
+}
+
+// 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 — remember filtered list, use method reference or remembered lambda
+val activeItems = remember(items) { items.filter { it.isActive } }
+activeItems.forEach { ActiveItem(it, onClick = remember { { handle(it) } }) }
+```
+
+## 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.