BaseViewModel with STATE

abstract class BaseViewModel<STATE: Parcelable>(
    private val savedStateHandle: SavedStateHandle,
    private val defaultState: STATE
): ViewModel() {

    private val KEY_STATE = "state"

    val state: StateFlow<STATE> = savedStateHandle.getStateFlow(KEY_STATE, defaultState)

    protected fun updateState(newState: STATE.() -> STATE) {
        // see DataStore updateData
        // get current state
        savedStateHandle.get<STATE>(KEY_STATE)?.let { state ->
            // simpan state baru ke savedStateHandle
            savedStateHandle[KEY_STATE] = newState(state)
        }
    }
}

@Parcelize
data class MyState(
    val text: String = ""
): Parcelable

@HiltViewModel
class MyViewModel @Inject constructor(
    savedStateHandle: SavedStateHandle
): BaseViewModel<MyState>(
    savedStateHandle = savedStateHandle,
    defaultState = MyState()
) {

    fun updateText(newText: String) {
        updateState {
            copy(
                text = newText
            )
        }
    }
}

@Composable
fun MyScreen(
    viewModel: MyViewModel = hiltViewModel()
) {

    // Observe state
    val state by viewModel.state.collectAsStateWithLifecycle()

    Box(
        contentAlignment = Alignment.Center,
        modifier = Modifier
            .fillMaxSize()
    ) {
        OutlinedTextField(
            value = state.text,
            onValueChange = viewModel::updateText
        )
    }
}

@AndroidEntryPoint
class MainActivity : ComponentActivity() {
    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContent {
            ComposeResearchTheme {
                Surface(
                    modifier = Modifier.fillMaxSize(),
                    color = MaterialTheme.colorScheme.background
                ) {
                    MyScreen()
                }
            }
        }
    }
}