What You'll Learn
How to use SavedStateHandle to preserve ViewModel state across process death.
Why SavedStateHandle?
Regular ViewModel variables live in memory only — they're lost on process death. SavedStateHandle saves state via Bundle, surviving process death and restoration.
Basic Usage
class SearchViewModel(
private val savedStateHandle: SavedStateHandle
) : ViewModel() {
val query: StateFlow<String> = savedStateHandle.getStateFlow("query", "")
val selectedTab: StateFlow<Int> = savedStateHandle.getStateFlow("selectedTab", 0)
fun updateQuery(newQuery: String) { savedStateHandle["query"] = newQuery }
fun selectTab(index: Int) { savedStateHandle["selectedTab"] = index }
}
Navigation Arguments
class UserDetailViewModel(savedStateHandle: SavedStateHandle) : ViewModel() {
private val userId: String = checkNotNull(savedStateHandle["userId"])
init { loadUser(userId) }
}
With Hilt
@HiltViewModel
class TodoViewModel @Inject constructor(
private val repository: TodoRepository,
private val savedStateHandle: SavedStateHandle
) : ViewModel() {
val filter: StateFlow<String> = savedStateHandle.getStateFlow("filter", "all")
val todos = filter.flatMapLatest { f ->
when (f) {
"active" -> repository.getActiveTodos()
else -> repository.getAllTodos()
}
}.stateIn(viewModelScope, SharingStarted.Lazily, emptyList())
}
Summary
SavedStateHandlefor process death survival
getStateFlow()for reactive state management- Navigation arguments via SavedStateHandle
- Hilt auto-injection support
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