Issue
The following code is from the official Advanced State in Jetpack Compose Codelab.
In the function fun DetailsScreen(), uiState.isLoading -> {...} will be fired when isLoading is true.
I searched all the code in the project, I can only find the code val uiState by produceState(initialValue = DetailsUiState(isLoading = true)) to pass value to isLoading.
Will uiState.isLoading -> {...} always be fired in the project?
data class DetailsUiState(
val cityDetails: ExploreModel? = null,
val isLoading: Boolean = false,
val throwError: Boolean = false
)
@Composable
fun DetailsScreen(
onErrorLoading: () -> Unit,
modifier: Modifier = Modifier,
viewModel: DetailsViewModel = viewModel()
) {
val uiState by produceState(initialValue = DetailsUiState(isLoading = true)) {
val cityDetailsResult = viewModel.cityDetails
value = if (cityDetailsResult is Result.Success<ExploreModel>) {
DetailsUiState(cityDetailsResult.data)
} else {
DetailsUiState(throwError = true)
}
}
when {
uiState.cityDetails != null -> {
DetailsContent(uiState.cityDetails!!, modifier.fillMaxSize())
}
uiState.isLoading -> {
Box(modifier.fillMaxSize()) {
CircularProgressIndicator(
color = MaterialTheme.colors.onSurface,
modifier = Modifier.align(Alignment.Center)
)
}
}
else -> { onErrorLoading() }
}
}
@HiltViewModel
class DetailsViewModel @Inject constructor(
private val destinationsRepository: DestinationsRepository,
savedStateHandle: SavedStateHandle
) : ViewModel() {
private val cityName = savedStateHandle.get<String>(KEY_ARG_DETAILS_CITY_NAME)!!
val cityDetails: Result<ExploreModel>
get() {
val destination = destinationsRepository.getDestination(cityName)
return if (destination != null) {
Result.Success(destination)
} else {
Result.Error(IllegalArgumentException("City doesn't exist"))
}
}
}
sealed class Result<out R> {
data class Success<out T>(val data: T) : Result<T>()
data class Error(val exception: Exception) : Result<Nothing>()
}
Solution
No
The default value of isLoading is false:
val isLoading: Boolean = false,
So the constructor calls that don't explicitly set it to true (DetailsUiState(throwError = true) and DetailsUiState(throwError = true)) will result in it being false.
Answered By - Ryan M
