如何通过 ViewModel 从 Fragment 观察 Repository LiveData

Question

我很难弄清楚如何在 @GET 请求的情况下连接我的 Repository 和 ViewModel 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 并且每当正文更改时，存储库的函数都会被调用并实时向响应发出值数据是这样的

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，我的视图提供了几个查询参数

我在存储库 class 中调用了此改造 API，代码如下所示

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)
        }
    }

主要问题是我想观察 checkInResponse 的方式与我观察 @POST 请求的方式相同，但不知道如何传递观察存储库 LiveData，就像我对 post 上面的请求使用 Transformations.switchMap。谁能帮我处理这个案子？

编辑 - 这是我的改造服务 class 按要求

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

试试这个：

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)
    }
}

Answer 2

您想要的方法可以使用中间 LiveData 来保存请求参数，名为 queryLiveData。当 checkInCheckOut 函数被调用时，我们为它设置一个新值，导致 checkInResponse 发生变化。然后变化将转化为repository.checkInCheckOutUser的结果使用switchMap.

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

Transformations.switchMap()只是利用MediatorLiveData。由于您的用例有点不同，您可以直接自己实现它。

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
        }
    }
}

此代码假设 data 仅发出一个终端元素 Resource.Success 或 Resource.Failure 并用它清理源。

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