不确定如何使用 DAO 将 Cursor 转换为此方法的返回类型

Question

我对 DAO 接口中的返回类型有疑问。 我已经进行了研究，并且尝试在不挂起/挂起的情况下进行，但仍然相同。

Error: Not sure how to convert a Cursor to this method's return type ...

道

    @Query("SELECT * FROM notification_list ORDER BY id ASC")
    abstract fun readAllDataState(): DataState<List<NotificationItemsResponse.NotificationItemData>>

我的用例：

class GetNotificationListItemDetailsUseCase @Inject constructor(private val notificationDao: NotificationDao): BaseFlowUseCase<Unit, DataState<List<NotificationItemsResponse.NotificationItemData>>>() {
    override fun create(params: Unit): Flow<DataState<List<NotificationItemsResponse.NotificationItemData>>> {
        return flow{
            emit(DataState.Loading)

            try {
                emit(DataState.Success(notificationDao.readAllDataState()))
            } catch(e: Exception) {
                emit(DataState.Error(e)) // error, and send the exception
            }

视图模型

    val notificationData = MutableStateFlow<List<NotificationItemsResponse.NotificationItemData>>(emptyList())

[..]
    fun getActualState() {
        viewModelScope.launch {
            getNotificationListItemDetailsUseCase.build(Unit).collect {
                notificationData.value = it
                Log.d("test2", "${notificationData.value}")

            }
        }
    }

分段

        GlobalScope.launch { collectNotificationItems() }

[..]

    private suspend fun collectNotificationItems() {
        vm.notificationData.collectLatest { dataState ->
            when(dataState) {
                is DataState.Error -> {
                    collectErrorState()
                    Log.d("collectNotificationItems", "Collect ErrorState")
                }
                DataState.Loading -> {
                    Log.d("collectNotificationItems", "Collect Loading")
                }
                is DataState.Success<*> -> {
                    vm.notificationData.collectWith(viewLifecycleOwner) {
                        notificationAdapter.items = it
                        notificationAdapter.notifyDataSetChanged()
                        Log.d("collectNotificationItems", "Collect Sucess")
                    }
                }
            }
        }

上面有所有细节我希望它足以解决这个问题。

Answer 1

Room 不知道如何返回 DataState 类型。 readAllDataState()的返回类型更改为List<NotificationItemsResponse.NotificationItemData>并使 function suspend ，这样，每次调用只会获得一个值。 然后，只需将返回值包装在emit(DataState.Success(returnedValue))中。 像这样：

@Query("SELECT * FROM notification_list ORDER BY id ASC")
abstract suspend fun readAllDataState(): List<NotificationItemsResponse.NotificationItemData>

class GetNotificationListItemDetailsUseCase @Inject constructor(private val notificationDao: NotificationDao): BaseFlowUseCase<Unit, DataState<List<NotificationItemsResponse.NotificationItemData>>>() {

  override fun create(params: Unit): Flow<DataState<List<NotificationItemsResponse.NotificationItemData>>> = 
    flow {
        emit(DataState.Loading)
        try {
          emit(DataState.Success(notificationDao.readAllDataState()))
        } catch(e: Exception) {
          emit(DataState.Error(e)) // error, and send the exception
        }
    }