Will the value of isLoading be always true in the Android Jetpack Compose project?

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

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