在 Android Jetpack Compose 项目中，isLoading 的值会一直为真吗？

Question

以下代码来自官方Advanced State in Jetpack Compose Codelab。

在函数fun DetailsScreen()中，uiState.isLoading -> {...}会在isLoading为真时被触发。

我搜索了项目中的所有代码，只能找到代码val uiState by produceState(initialValue = DetailsUiState(isLoading = true))传值​​给isLoading。

uiState.isLoading -> {...} 在项目中总是会被解雇吗？

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>()
}

Answer 1

没有

isLoading的默认值为false：

val isLoading: Boolean = false,

因此，未将其显式设置为true（DetailsUiState(throwError = true) 和DetailsUiState(throwError = true)）的构造函数调用将导致它为false。