如何通过ViewModel从片段观察存储库LiveData

Question

[我很难确定在Repository请求的情况下如何连接ViewModel和@GET的实时数据，并在片段中观察它们。

[当请求类型为@POST时我没有这个问题，因为我可以在正文上使用Transformation.switchMap，并且每当正文更改存储库的功能时就会调用它并向响应实时数据发出值，就像这样

val matchSetsDetail: LiveData<Resource<MatchDetailBean>> = Transformations.switchMap(matchIdLiveData) { matchId ->
        val body = MatchSetRequest(matchId)
        repository.getMatchSet(body)
    }

但是在@GET请求的情况下，我有几个View参数提供的查询参数

我在存储库类中有此改造API调用，代码看起来像这样

class Repository {
    fun checkInCheckOutUser(apiKey: String, userId: Int, status: String, latitude: Double, longitude: Double, checkedOn: Long): LiveData<Resource<BaseResponse>> = liveData {
            emit(Resource.Loading())
            try {
                val response: Response<BaseResponse> = ApiClient.coachApi.checkInCheckOutUser(apiKey, userId, status, latitude, longitude, checkedOn)
                if (response.isSuccessful && response.body() != null) {
                    if (response.body()!!.isValidKey && response.body()!!.success) {
                        emit(Resource.Success(response.body()!!))
                    } else {
                        emit(Resource.Failure(response.body()!!.message))
                    }
                } else {
                    emit(Resource.Failure())
                }
            } catch (e: Exception) {
                emit(Resource.Failure())
            }
        }
}

和ViewModel

class CheckInMapViewModel : ViewModel() {
    val checkInResponse: LiveData<Resource<BaseResponse>> = MutableLiveData()

        fun checkInCheckOut(apiKey: String, userId: Int, status: String, latitude: Double, longitude: Double, checkedOn: Long): LiveData<Resource<BaseResponse>> {
            return repository.checkInCheckOutUser(apiKey,userId,status,latitude,longitude,checkedOn)
        }
    }

[主要问题是我想以与checkInResponse请求相同的方式观察@POST，但不像我上面使用Transformations.switchMap处理我的发布请求那样，不知道如何传递观察存储库LiveData。有人可以帮助我处理此案吗？

编辑-这是我要求的翻新服务类

interface CoachApi {
    @POST(Urls.CHECK_IN_CHECK_OUT_URL)
    suspend fun checkInCheckOutUser(
        @Query("apiKey") apiKey: String,
        @Query("userId") userId: Int,
        @Query("status") status: String,
        @Query("latitude") latitude: Double,
        @Query("longitude") longitude: Double,
        @Query("checkedOn") checkedOn: Long
    ): Response<SelfCheckResponse>

    @POST(Urls.SELF_CHECK_STATUS)
    suspend fun getCheckInStatus(
        @Query("apiKey") apiKey: String,
        @Query("userId") userId: Int
    ): Response<SelfCheckStatusResponse>
}

Answer 1

Transformations.switchMap()仅使用MediatorLiveData。由于您的用例有些不同，因此您可以直接自己实现。

class CheckInMapViewModel : ViewModel() {
    private val _checkInResponse = MediatorLiveData<Resource<BaseResponse>>
    val checkInResponse: LiveData<Resource<BaseResponse>> = _checkInResponse

    fun checkInCheckOut(apiKey: String, userId: Int, status: String, latitude: Double, longitude: Double, checkedOn: Long) {
        val data = repository.checkInCheckOutUser(apiKey,userId,status,latitude,longitude,checkedOn)
        _checkInResponse.addSource(data) {
            if (it is Resource.Success || it is Resource.Failure)
                _checkInResponse.removeSource(data)
            _checkInResponse.value = it
        }
    }
}

此代码假定data仅发射一个端子元素Resource.Success或Resource.Failure，并用其清除源。

Answer 2

[您期望的方法可以使用中间存储LiveData，该中间存储名为queryLiveData的请求参数。调用checkInCheckOut函数时，我们为其设置了一个新值，从而导致checkInResponse发生变化。然后，将使用repository.checkInCheckOutUser将更改转换为switchMap的结果。

CheckInMapViewModel：

class CheckInMapViewModel : ViewModel() {

    private val queryLiveData = MutableLiveData<CheckInCheckOutParam?>()

    init {
        queryLiveData.postValue(null)
    }

    val checkInResponse: LiveData<Resource<BaseResponse>> =
        queryLiveData.switchMap { query ->
            if(query == null) {
                AbsentLiveData.create()
            } else {
                repository.checkInCheckOutUser(
                    query.apiKey,
                    query.userId,
                    query.status,
                    query.latitude,
                    query.longitude,
                    query.checkedOn
                )
            }
        }

    fun checkInCheckOut(
        apiKey: String,
        userId: Int,
        status: String,
        latitude: Double,
        longitude: Double,
        checkedOn: Long
    ) {
        queryLiveData.postValue(
            CheckInCheckOutParam(apiKey, userId, status, latitude, longitude, checkedOn)
        )
    }

    private data class CheckInCheckOutParam(
        val apiKey: String,
        val userId: Int,
        val status: String,
        val latitude: Double,
        val longitude: Double,
        val checkedOn: Long
    )
}

AbsentLiveData：

/**
 * A LiveData class that has `null` value.
 */
class AbsentLiveData<T : Any?> private constructor(resource: Resource<T>) :
    LiveData<Resource<T>>() {

    init {
        // use post instead of set since this can be created on any thread
        postValue(resource)
    }

    companion object {

        fun <T> create(): LiveData<Resource<T>> {
            return AbsentLiveData(Resource.empty())
        }
    }
}

Answer 3

尝试一下：

class CheckInMapViewModel : ViewModel() {
    private val _checkInResponse: MediatorLiveData<Resource<BaseResponse>> = MediatorLiveData()
    val checkInResponse: LiveData<Resource<BaseResponse>>
    get() = _checkInResponse

    init {
        _checkInResponse.addSource(checkInCheckOut()) {
            _checkInResponse.value = it
        }
    }

    fun checkInCheckOut(apiKey: String, userId: Int, status: String, latitude: Double, longitude: Double, checkedOn: Long): LiveData<Resource<BaseResponse>> {
        return repository.checkInCheckOutUser(apiKey,userId,status,latitude,longitude,checkedOn)
    }
}