Flowable的onErrorResumeNext出错，networkOnMainThread

Question

我有以下rxJava链：

 override fun combineLocationToPlace(req: Flowable<Place>): Flowable<Place> {
        var combinedFlowable = Flowable
                .combineLatest(
                        req,
                        getLastLocation().lastOrError().toFlowable(),
                        BiFunction<Place, Location, Place> { t1, location ->
                            Timber.w("FIRSTINIT - Retrieved location $location")
                            var placeLocation = Location(t1.placeName)
                            placeLocation.latitude = t1.latitude
                            placeLocation.longitude = t1.longitude
                            t1.distance = location.distanceTo(placeLocation)
                            t1
                        })


        return combinedFlowable
                .onErrorResumeNext { t: Throwable ->
                    Timber.w(t, "FIRSTINIT - Could not retrieve location for place (${t.message}) returning original request")
                    req
                }
                .doOnError {
                    Timber.w("FIRSTINIT - did detect the error here...")
                }

        return combinedFlowable
    }

简而言之，我正在从本地数据库(一个地点)检索一些数据，并希望将其与来自GPS的最新位置相结合：

 override fun getLastLocation(requestIfEmpty: Boolean): Observable<Location> {
        var lastLocation = locationProvider.lastKnownLocation
                .doOnNext {
                    Timber.w("Got location $it from last one")
                }
                .doOnComplete {
                    Timber.w("did i get a location?")
                }

        if (requestIfEmpty) {
            Timber.w("Switching to request of location")
            lastLocation = lastLocation.switchIfEmpty(requestLocation())
        }

        return lastLocation.doOnNext {
            Timber.w("Got something!")
            location = it
        }


    }

但我想说明用户没有最后一个位置的scneario，因此这一行：

return combinedFlowable
                    .onErrorResumeNext { t: Throwable ->
                        Timber.w(t, "FIRSTINIT - Could not retrieve location for place (${t.message}) returning original request")
                        req
                    }
                    .doOnError {
                        Timber.w("FIRSTINIT - did detect the error here...")
                    }

它试图捕获任何错误，并仅使用原始请求重试，而不将其与任何内容相结合。我这样调用这段代码：

fun getPlace(placeId: String) {
        locationManager.combineLocationToPlace(placesRepository.getPlace(placeId))
                .onErrorResumeNext { t: Throwable ->
                    Timber.e(t, "Error resuming next! ")
                    placesRepository.getPlace(placeId)
                }.subscribeOn(schedulerProvider.io()).observeOn(schedulerProvider.ui())
                .subscribeBy(
                        onNext = {
                            place.value = Result.success(it)
                        },
                        onError = {
                            Timber.e("ERROR! $it")
                            place.value = Result.failure(it)
                        }
                )
                .addTo(disposables)

    }

但是，当没有位置抛出NoSuchElementException时，我的flowable会切换到原始请求，然后在执行它时会得到一个NetworkOnMainThread异常。这个请求不应该在我放在里面的scheduler.io()上执行吗(因为我把代码放在前面了)？

如果你想知道，schedulerProvider.io()翻译成：

Schedulers.io()

GetPlace：

  /**
     * Retrieves a single place from database
     */
      override fun getPlace(id: String): Flowable<Place> {
        return Flowable.merge(placesDao.getPlace(id),
                refreshPlace(id).toFlowable())
    }

    /**
     * Triggers a refreshPlace update on the db, useful when changing stuff associated with the place
     * itself indirectly (e.g. an experience)
     */
    private fun refreshPlace(id: String): Single<Place> {
        return from(placesApi.getPlace(id))
                .doOnSuccess {
                    placesDao.savePlace(it)
                }
    }

Answer 1

为了确保您的网络发生在主线程之外，请显式地将其发送到后台线程。

使用Rx调度程序类中的IO、New Thread或Computation调度程序：

subscribeOn(Schedulers.computation())

对于您不想这样做的情况(或者如果您认为它应该已经在后台线程上并且只想调试)，您可以按如下方式记录线程信息：

Thread.currentThread().getName()

如果您对观察和订阅使用不同的调度程序，则这对于跟踪使用Schedulers.trampoline()或时发生的情况特别有用：

.subscribeOn(schedulerProvider.io()).observeOn(schedulerProvider.ui())

Answer 2

你不能使用onErrorResumeNext来实现这种功能。你应该使用retryWhen运算符。

也许这篇文章对你很有用。

https://medium.com/@v.danylo/server-polling-and-retrying-failed-operations-with-retrofit-and-rxjava-8bcc7e641a5a

此代码使用backoff轮询服务器，直到收到与204不同的代码。也许您可以使用retryWhen而不是repeatWhen来适应您的需求。

  fun pollServerWithBackoff(videoId: String, maxAttempts: Int, delay: Int): Flowable<Response<ResponseBody>> {
        return api.download(videoId)
                .subscribeOn(Schedulers.io())
                .repeatWhen {
                    it
                            .zipWith(Flowable.range(1, maxAttempts),
                                    BiFunction { _: Any?, attempt: Int -> attempt })
                            .flatMap {

                                Flowable.timer((it * delay).toLong(), TimeUnit.SECONDS);
                            }

                }
                .takeUntil({

                    it.code() != 204
                })
                .filter {

                    it.code() != 204
                }
                .map{
                    if(it.code() in 200..300)
                        it
                    else
                        throw IOException(it.errorBody()?.toString() ?: "Unkown Error")
                }
    }