Android：使用 kotlin 流时 Firebase 对象为空

Question

我的问题是，当我尝试从我的数据库中获取文档时，该文档又名对象始终为空。我只有在使用 Kotlin Coroutines 从我的数据库中获取文档时才会遇到这个问题。对听众使用标准方法确实有效。

电子邮件存储库

interface EmailRepository {
    suspend fun getCalibratePrice(): Flow<EmailEntity?>
    suspend fun getRepairPrice(): Flow<EmailEntity?>
}

EmailRepository 实现

class EmailRepositoryImpl @Inject constructor(private val db: FirebaseFirestore) : EmailRepository {

    fun hasInternet(): Boolean {
        return true
    }

    // This works! When using flow to write a document, the document is written!
    override fun sendEmail(email: Email)= flow {
        emit(EmailStatus.loading())
        if (hasInternet()) {
            db.collection("emails").add(email).await()
            emit(EmailStatus.success(Unit))
        } else {
            emit(EmailStatus.failed<Unit>("No Email connection"))
        }
    }.catch {
        emit(EmailStatus.failed(it.message.toString()))
    }.flowOn(Dispatchers.Main)


    // This does not work! "EmailEntity" is always null. I checked the document path!
    override suspend fun getCalibratePrice(): Flow<EmailEntity?> = flow {
        val result = db.collection("emailprice").document("Kalibrieren").get().await()
        emit(result.toObject<EmailEntity>())
    }.catch {

    }.flowOn(Dispatchers.Main)


    // This does not work! "EmailEntity" is always null. I checked the document path!
    override suspend fun getRepairPrice(): Flow<EmailEntity?> = flow {
        val result = db.collection("emailprice").document("Reparieren").get().await()
        emit(result.toObject<EmailEntity>())
    }.catch {

    }.flowOn(Dispatchers.Main)
}

获取数据的Viewmodel

init {
        viewModelScope.launch {
            withContext(Dispatchers.IO) {
                if (subject.value != null){
                    when(subject.value) {
                        "Test" -> {
                            emailRepository.getCalibratePrice().collect {
                                emailEntity.value = it
                            }
                        }
                        "Toast" -> {
                            emailRepository.getRepairPrice().collect {
                                emailEntity.value = it
                            }
                        }
                    }
                }
            }
        }
    }

private val emailEntity = MutableLiveData<EmailEntity?>()

private val _subject = MutableLiveData<String>()
val subject: LiveData<String> get() = _subject

片段

@AndroidEntryPoint
class CalibrateRepairMessageFragment() : EmailFragment<FragmentCalibrateRepairMessageBinding>(
    R.layout.fragment_calibrate_repair_message,
) {
    // Get current toolbar Title and send it to the next fragment.
    private val toolbarText: CharSequence by lazy { toolbar_title.text }

    override val viewModel: EmailViewModel by navGraphViewModels(R.id.nav_send_email) { defaultViewModelProviderFactory }

    override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
        super.onViewCreated(view, savedInstanceState)
        // Here I set the data from the MutableLiveData "subject". I don't know how to do it better
        viewModel.setSubject(toolbarText.toString())
    }
}

有人会说，Firebase 规则是这里的问题，但这里不应该是这种情况，因为数据库是开放的并且使用侦听器方法确实有效。

我从 CalibrateRepairMessageFragment 得到了 subject.value。当我不检查 if(subject.value != null) 时，我从 init 块中得到 NullPointerException。

我将只在我的 viewModel 中使用 emailEntitiy，而不是在它之外。

非常感谢您的帮助，谢谢。

编辑

这是我获取数据的新方式。该对象仍然为空！我还在我的挂起函数中添加了 Timber.d 消息，这些消息也永远不会被执行，因此流程永远不会抛出错误。使用这种新方法，我不再得到 NullPointerException

private val emailEntity = liveData {
    when(subject.value) {
        "Test" -> emailRepository.getCalibratePrice().collect {
            emit(it)
        }
        "Toast" -> emailRepository.getRepairPrice().collect {
            emit(it)
        }
        // Else block is never executed, therefore "subject.value" is either Test or toast and the logic works. Still error when using flow!
        else -> EmailEntity("ERROR", 0F)
    }
}

我在我的一个函数中使用 Timber.d("EmailEntity is ${emailEntity.value}") 检查 emailEntity 是否为 null。

然后我用 val price = MutableLiveData(emailEntity.value?.basePrice ?: 1000F) 设置价格但是因为 emailentity 是 null 所以价格总是 1000

编辑 2

我现在对问题进行了进一步的研究，向前迈进了一大步。当从像 CalibrateRepairMessageFragment 这样的片段观察 emailEntity 时， 值不再是 null.

此外，在观察emailEntity时，值在viewModel中也不是null，而是在一个片段中观察到的！那么我如何从我的 viewModel 中观察 emailEntity 或从我的 repository 中获取值并在我的 viewmodel 中使用它？

Answer 1

好的，我的问题已经解决了，这是最终的解决方案：

状态class

sealed class Status<out T> {
    data class Success<out T>(val data: T) : Status<T>()
    class Loading<T> : Status<T>()
    data class Failure<out T>(val message: String?) : Status<T>()

    companion object {
        fun <T> success(data: T) = Success<T>(data)
        fun <T> loading() = Loading<T>()
        fun <T> failed(message: String?) = Failure<T>(message)
    }
}

电子邮件存储库

interface EmailRepository {
    fun sendEmail(email: Email): Flow<Status<Unit>>
    suspend fun getCalibratePrice(): Flow<Status<CalibrateRepairPricing?>>
    suspend fun getRepairPrice(): Flow<Status<CalibrateRepairPricing?>>
}

EmailRepositoryImpl

class EmailRepositoryImpl (private val db: FirebaseFirestore) : EmailRepository {
    fun hasInternet(): Boolean {
        return true
    }

    override fun sendEmail(email: Email)= flow {
        Timber.d("Executed Send Email Repository")
        emit(Status.loading())
        if (hasInternet()) {
            db.collection("emails").add(email).await()
            emit(Status.success(Unit))
        } else {
            emit(Status.failed<Unit>("No Internet connection"))
        }
    }.catch {
        emit(Status.failed(it.message.toString()))
    }.flowOn(Dispatchers.Main)

    // Sends status and object to viewModel
    override suspend fun getCalibratePrice(): Flow<Status<CalibrateRepairPricing?>> = flow {
        emit(Status.loading())
        val entity = db.collection("emailprice").document("Kalibrieren").get().await().toObject<CalibrateRepairPricing>()
        emit(Status.success(entity))
    }.catch {
        Timber.d("Error on getCalibrate Price")
        emit(Status.failed(it.message.toString()))
    }

    // Sends status and object to viewModel
    override suspend fun getRepairPrice(): Flow<Status<CalibrateRepairPricing?>> = flow {
        emit(Status.loading())
        val entity = db.collection("emailprice").document("Kalibrieren").get().await().toObject<CalibrateRepairPricing>()
        emit(Status.success(entity))
    }.catch {
        Timber.d("Error on getRepairPrice")
        emit(Status.failed(it.message.toString()))
    }
}

视图模型

private lateinit var calibrateRepairPrice: CalibrateRepairPricing

private val _calirateRepairPriceErrorState = MutableLiveData<Status<Unit>>()
val calibrateRepairPriceErrorState: LiveData<Status<Unit>> get() = _calirateRepairPriceErrorState

init {
        viewModelScope.launch {
            when(_subject.value.toString()) {
                "Toast" -> emailRepository.getCalibratePrice().collect {
                    when(it) {
                        is Status.Success -> {
                            calibrateRepairPrice = it.data!!
                            _calirateRepairPriceErrorState.postValue(Status.success(Unit))
                        }
                        is Status.Loading -> _calirateRepairPriceErrorState.postValue(Status.loading())
                        is Status.Failure -> _calirateRepairPriceErrorState.postValue(Status.failed(it.message))
                    }
                }
                else -> emailRepository.getRepairPrice().collect {
                    when(it) {
                        is Status.Success -> {
                            calibrateRepairPrice = it.data!!
                            _calirateRepairPriceErrorState.postValue(Status.success(Unit))
                        }
                        is Status.Loading -> _calirateRepairPriceErrorState.postValue(Status.loading())
                        is Status.Failure -> _calirateRepairPriceErrorState.postValue(Status.failed(it.message))
                    }
                }
            }
            price.postValue(calibrateRepairPrice.head!!.basePrice)
        }
    }

您现在可以在您的一个片段中观察状态（但您不需要！）

片段

viewModel.calibrateRepairPriceErrorState.observe(viewLifecycleOwner) { status ->
            when(status) {
                is Status.Success -> requireContext().toast("Price successfully loaded")
                is Status.Loading -> requireContext().toast("Price is loading")
                is Status.Failure -> requireContext().toast("Error, Price could not be loaded")
            }
        }

这是我的 toast 扩展功能：

fun Context.toast(text: String, duration: Int = Toast.LENGTH_SHORT) {
    Toast.makeText(this, text, duration).show()
}

Android：使用 kotlin 流时 Firebase 对象为空

Android: Firebase Object is null when using kotlin flow

android

kotlin

android-mvvm

android-livedata

google-cloud-firestore

电子邮件存储库

EmailRepository 实现

获取数据的Viewmodel

片段

编辑

编辑 2

状态class

电子邮件存储库

EmailRepositoryImpl

视图模型

片段