Android ViewModel Recreation: Fixing the Rotation State Trap

Android ViewModel Recreation: Fixing the Rotation State Trap

Rotation bugs usually appear as “random resets.” The root cause is state living in views instead of a lifecycle-aware model.

Step 1: Move UI state to immutable model snapshots

data class QuizUiState(
    val questionIndex: Int = 0,
    val selectedAnswer: Int? = null,
    val score: Int = 0
)

Step 2: Expose state from ViewModel only

class QuizViewModel : ViewModel() {
    private val _state = MutableStateFlow(QuizUiState())
    val state: StateFlow<QuizUiState> = _state
}

Step 3: Persist critical fields via SavedStateHandle

handle["questionIndex"] = newIndex

Pitfalls

• Keeping selection state inside composables only.
• Using activity fields as temporary source of truth.
• No rotation test cases in instrumentation suite.

Validation

• Rotate screen mid-quiz and state remains intact.
• Background/foreground cycle preserves progress.
• ViewModel remains single source of truth.