compose-state-holder-ui-split

Compose: state holder/UI split

Core principle

Separate state-holder wiring from UI rendering. The state-holder composable talks to ViewModels, components, flows, navigation, and side effects. The UI composable takes plain immutable UI state plus callbacks and describes layout.

This keeps screens previewable, testable, and easier to reuse across Android, Desktop, TV, and KMP/CMP targets.

When to use this skill

Use this when a Compose screen:

• Takes a ViewModel, component, controller, navigator, repository, or service directly.
• Collects app/business state or side effects in the same function that lays out most UI.
• Passes a whole state holder into child composables instead of explicit state and callbacks.
• Is hard to preview because it needs dependency injection, navigation, lifecycle, or fake services.
• Has UI tests that must construct a full app stack to verify a simple layout branch.

The pattern

Use a small public state-holder composable:

@Composable
fun ProfileScreen(component: ProfileComponent, modifier: Modifier = Modifier) {
    val state by component.state.collectAsStateWithLifecycle()

    ProfileScreen(
        state = state,
        onNameChange = component::onNameChange,
        onSaveClick = component::save,
        onBackClick = component::back,
        modifier = modifier,
    )
}

Then put UI in a plain composable that knows nothing about the state holder:

@Composable
fun ProfileScreen(
    state: ProfileUiState,
    onNameChange: (String) -> Unit,
    onSaveClick: () -> Unit,
    onBackClick: () -> Unit,
    modifier: Modifier = Modifier,
) {
    ProfileContent(
        name = state.name,
        isSaving = state.isSaving,
        canSave = state.canSave,
        onNameChange = onNameChange,
        onSaveClick = onSaveClick,
        onBackClick = onBackClick,
        modifier = modifier,
    )
}

Private content functions can break up layout:

@Composable
private fun ProfileContent(
    name: String,
    isSaving: Boolean,
    canSave: Boolean,
    onNameChange: (String) -> Unit,
    onSaveClick: () -> Unit,
    onBackClick: () -> Unit,
    modifier: Modifier = Modifier,
) {
    // Layout only.
}