lambda - 将两个 Observables 的平面图的 lambda 更改为两个 Singles 的平面图时出错

Question

我想合并两个 API 请求的结果。最初我让它们返回 Observable，但为了正确执行它，我猜响应应该是 Single。

这是我最初的改造接口(interface):

interface RemoteGeocodingService {

@GET("json")
fun requestCityAddressByName(
        @Query("address") address: String
): Observable<LocationResponse>
}

interface RemoteWeatherService {

@GET("{latitude},{longitude}")
fun requestWeatherForCity(
        @Path("latitude") latitude: String,
        @Path("longitude") longitude: String
): Observable<WeatherResponse>
}

我使用 lambda 像这样组合它们的结果:

    override fun getWeather(cityName: String): Observable<WeatherDetailsDTO>? {
    return remoteWeatherDataSource.requestCityAddressByName(cityName)
            .flatMap({ responseFromServiceA -> remoteWeatherDataSource.requestWeatherForCity(responseFromServiceA.results[0].geometry.location.lat.toString(), responseFromServiceA.results[0].geometry.location.lng.toString()) },
                    { responseFromServiceA, responseFromServiceB ->
                        TransformersDTO.transformToWeatherDetailsDTO(responseFromServiceA.results[0].formatted_address, responseFromServiceB)
                    })
            .retry()
}

但是，当我将每个 API 接口(interface)方法的请求结果更改为使用 Single 而不是 Observable 时，我无法执行此操作 - 我在 Android Studio IDE 编辑器中出现错误。这是我尝试过的:

  override fun getWeather(cityName: String): Single<WeatherDetailsDTO> {
    return remoteWeatherDataSource.requestCityAddressByName(cityName)
            .flatMap({ responseFromServiceA: LocationResponse -> remoteWeatherDataSource.requestWeatherForCity(responseFromServiceA.results[0].geometry.location.lat.toString(), responseFromServiceA.results[0].geometry.location.lng.toString()) },
                    { responseFromServiceA: LocationResponse, responseFromServiceB: WeatherResponse ->
                        TransformersDTO.transformToWeatherDetailsDTO(responseFromServiceA.results[0].formatted_address, responseFromServiceB)
                    })
            .retry()

IDE 标记为错误 .flatMap 运算符并说:

None of the following functions can be called with the arguments supplied. flatMap(((t: LocationResponse) → SingleSource!)!)   where R cannot be inferred for   fun flatMap(mapper: ((t: LocationResponse) → SingleSource!)!): Single! defined in io.reactivex.Single flatMap(Function!>!)   where R cannot be inferred for   fun flatMap(mapper: Function!>!): Single! defined in io.reactivex.Single

如何解决？

Answer 1

没有Single.flatMap(Function, BiFunction)方法。您必须映射到内部结果才能使项目配对:

remoteWeatherDataSource.requestCityAddressByName(cityName)
    .flatMap({ a: LocationResponse ->
        remoteWeatherDataSource.requestWeatherForCity(
            a.results[0].geometry.location.lat.toString(), 
            a.results[0].geometry.location.lng.toString()
        )
        .map { b: WeatherResponse ->
            TransformersDTO.transformToWeatherDetailsDTO(
                a.results[0].formatted_address, 
                b
            )
        } 
    })