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Compose Rules

Based on NowInAndroid Compose patterns.

State Management

  • MUST hoist state to caller: Composable receives state + event callbacks
  • MUST use remember for expensive computations in Composable scope
  • MUST use rememberSaveable for state that survives configuration changes
  • MUST collect Flow with collectAsStateWithLifecycle()
  • MUST NOT modify state directly inside Composable — emit events to ViewModel
// NIA pattern: Screen receives state, delegates actions
@Composable
fun ForYouScreen(
    uiState: ForYouUiState,
    onTopicCheckedChanged: (String, Boolean) -> Unit,
) { /*...*/ }

Recomposition

  • MUST use stable/immutable types for Composable parameters
  • MUST annotate custom models with @Immutable or @Stable
  • MUST use key() in loops and dynamic lists
  • SHOULD use derivedStateOf for values derived from frequently-changing state
  • MUST NOT allocate objects (lists, maps, lambdas) without remember
  • MUST NOT perform side effects during composition

Side Effects

  • MUST use LaunchedEffect for composition-scoped coroutine side effects
  • MUST use DisposableEffect for cleanup-required side effects
  • SHOULD use rememberCoroutineScope() for user-triggered coroutines
  • MUST NOT call viewModelScope.launch from Composable

Composable Design

  • MUST accept Modifier as first optional parameter
  • MUST keep Composables small — extract at ~50 lines
  • MUST provide @Preview with sample data for public Composables
  • SHOULD separate stateful (container) and stateless (UI) Composables
  • MUST NOT use mutable collections as Composable parameters

Lazy Lists

  • MUST provide stable key in LazyColumn/LazyRow items
  • MUST use contentType for heterogeneous lists
  • MUST NOT nest LazyColumn inside verticalScroll Column — runtime crash
// NIA pattern: single LazyColumn with mixed content
LazyColumn {
    item { Header() }
    items(newsResources, key = { it.id }, contentType = { "newsResource" }) {
        NewsResourceCard(it)
    }
}

Theme

  • MUST use MaterialTheme tokens (colorScheme, typography, shapes)
  • MUST support light/dark theme
  • MUST NOT hardcode colors, font sizes, or dimensions

Interop (XML ↔ Compose)

  • MUST use ComposeView to embed Compose in XML
  • MUST use AndroidView to embed XML Views in Compose
  • SHOULD migrate bottom-up: leaf components first, then containers

Skills: /compose-animation, /compose-performance, /compose-navigation, /compose-testing