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Android ViewModel & State Management

Instructions

Use ViewModel to hold state and business logic. It must outlive configuration changes.

1. UI State (StateFlow)

• What : Represents the persistent state of the UI (e.g., Loading, Success(data), Error).

• Type : StateFlow<UiState>.

• Initialization : Must have an initial value.

• Exposure : Expose as a read-only StateFlow backing a private MutableStateFlow.

  private val _uiState = MutableStateFlow<UiState>(UiState.Loading)
  

  val uiState: StateFlow<UiState> = _uiState.asStateFlow()

• Updates : Update state using .update { oldState -> ... } for thread safety.

2. One-Off Events (SharedFlow)

• What : Transient events like "Show Toast", "Navigate to Screen", "Show Snackbar".

• Type : SharedFlow<UiEvent>.

• Configuration : Must use replay = 0 to prevent events from re-triggering on screen rotation.

  private val _uiEvent = MutableSharedFlow<UiEvent>(replay = 0)
  

  val uiEvent: SharedFlow<UiEvent> = _uiEvent.asSharedFlow()

• Sending : Use .emit(event) (suspend) or .tryEmit(event).

3. Collecting in UI

• Compose : Use collectAsStateWithLifecycle() for StateFlow.

  val state by viewModel.uiState.collectAsStateWithLifecycle()
  

For SharedFlow, use LaunchedEffect with LocalLifecycleOwner.

• Views (XML) : Use repeatOnLifecycle(Lifecycle.State.STARTED) within a coroutine.

4. Scope

• Use viewModelScope for all coroutines started by the ViewModel.
• Ideally, specific operations should be delegated to UseCases or Repositories.

Weekly Installs

156

Repository

new-silvermoon/…t-skills

GitHub Stars

552

First Seen

Jan 27, 2026

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