Android 可组合的可见性不随状态变化而变化

我的状态为isLoading，当数值为true时，我try 显示为CircularProgressIndicator.

@Composable
fun ProductDetailScreen(
    viewModel: ProductDetailViewModel = hiltViewModel()
) {
    val productState = viewModel.productState.value
    LazyColumn{
        item {
            if (productState.isLoading)
                CircularProgressIndicator()
        }
    }
}

I'm using a Resource class for my API call results and in the repository I use this class to wrap my request result.
The problem is, although I'm returning Resource.Loading from the repository, the isLoading state is not being updated from ViewModel and the ProgressIndicator is not shown in my screen. What could be causing this behavior?

sealed class Resource<T>(
    val data: T? = null,
    val message: String? = null,
    val errorType: ExceptionMapper.Type? = null
) {
    class Success<T>(data: T?) : Resource<T>(data)
    class Error<T>(message: String, errorType: ExceptionMapper.Type, data: T? = null) : Resource<T>(data, message, errorType)
    class Loading<T>(isLoading: Boolean = true) : Resource<T>()
}  

Repository:

override suspend fun getProductComments(productId: Int): Resource<List<Comment>> {
        return try {
            Resource.Loading<List<Comment>>()
            delay(3000)
            Resource.Success(apiService.getComments(productId))
        } catch (t: Throwable) {
            val mappedException = ExceptionMapper.map(t)
            Resource.Error(message = t.message!!, errorType = mappedException.type)
        }
    }    

ViewModel:个

@HiltViewModel
class ProductDetailViewModel @Inject constructor(
    state: SavedStateHandle,
    private val productRepository: ProductRepository
) : ViewModel() {

    private val passedProduct = state.get<Product>(EXTRA_KEY_DATA)
    var productId = passedProduct?.id

    var productState = mutableStateOf(ProductState())
        private set

    init {
        getProductComments()
    }
    private fun getProductComments() {
            viewModelScope.launch {
                productId?.let { pId ->
                    when (val commentResult = productRepository.getProductComments(pId)) {
                        is Resource.Success -> {
                            commentResult.data?.let { comments ->
                                productState.value =
                                    productState.value.copy(
                                        comments = comments,
                                        error = null,
                                        isLoading = false
                                    )
                            }
                        }
                        is Resource.Error -> {
                            productState.value = productState.value.copy(
                                isLoadFailed = true,
                                isLoading = false,
                                error = commentResult.message
                            )
                        }
                        is Resource.Loading -> {
                            productState.value = productState.value.copy(
                                isLoadFailed = false,
                                isLoading = true,
                                error = null
                            )
                        }
                    }
                }
            }
        }
}