定期轮询后端 API 一定次数 - Retrofit & RxJava

Question

我希望在预定义的定期间隔内对后端调用进行一定次数的轮询。如果我在循环之间收到预期的有效负载，我想退出循环并更新 UI，否则终止轮询。

以下是我进行标准 http 调用时通常执行的代码。

//Response Model from backend API
public class ApplicationStatusResponse
{
public boolean isActive;
}

//Retrofit facade  
@POST(v1/api/applicationStatus)
Single<ApplicationStatusResponse> checkApplicationStatus(@Body ApplicationStatusRequest applicationRequest);


-----

DisposableSingleObserver<ApplicationStatusResponse> disposableSingleObserver = new DisposableSingleObserver<ApplicationStatusResponse>() {
    @Override
    public void onSuccess(ApplicationStatusResponse response) {
            // Update UI Here
    }

    @Override
    public void onError(Throwable e) {

    }
};

CompositeDisposable compositeDisposable = new CompositeDisposable();

// Following call works alaways works 
DisposableSingleObserver<ApplicationStatusResponse> disposable = originationRepo.checkApplicationStatus(applicationStatusRequest)
        .observeOn(schedulerProvider.mainThread())
        .subscribeWith(disposableSingleObserver);

compositeDisposable.add(disposable);

但是我在下面的代码中有点迷失了，语法错误，当从 Flowable.interval 调用时我无法使用相同的disposableSingleObserver，并且在我需要更新 UI 的用例方面需要帮助定期状态直到时间过去或状态处于活动状态，这首先发生，如果我收到 500 的 HTTP 状态代码，我也不会终止轮询，而是重复直到满足上述条件。

 //Help Needed here  when I need polling in regular interval - I am kind of the syntax error complain from Android Studio

int INITIAL_DELAY = 0;
int POLLING_INTERVAL = 1000;
int POLL_COUNT = 8;

disposable = Flowable
            .interval(INITIAL_DELAY, POLLING_INTERVAL, TimeUnit.MILLISECONDS)
            .map(x -> originationRepo.checkApplicationStatus(applicationStatusRequest))
            .take(POLL_COUNT) ??
            // How can I receive the response payload and update the UI

compositeDisposable.add(disposable);

提前感谢您的帮助。

Answer 1

（继续MyDogTom's answer，您还可以通过抛出自定义错误/异常“短路”可观察对象）

选项 3：

disposable = Flowable
        .interval(INITIAL_DELAY, POLLING_INTERVAL, TimeUnit.MILLISECONDS)
        .map(x -> originationRepo.checkApplicationStatus(applicationStatusRequest)) // .flatMap (?)
        .take(POLL_COUNT) //YES
        .doOnNext() // update UI here
        .map(response -> {
           if(!response.checkCondition()) {
             throw new ShortCircuitException();
           }
             return response.data();
        })
        .onErrorResumeNext(throwable -> (throwable instanceof ShortCircuitException)
            ? Observable.empty()
            : Observable.error(throwable))

Answer 2

选项#1使用filter + take(1)

disposable = Flowable
            .interval(INITIAL_DELAY, POLLING_INTERVAL, TimeUnit.MILLISECONDS)
            .map(x -> originationRepo.checkApplicationStatus(applicationStatusRequest))
            .take(POLL_COUNT) //YES
            .doOnNext() // update UI here
            .map(response -> ) // should stop condition. true - stop, false - continue
            .filter(!shouldContinue)
            .take(1)

选项#2使用Subject + takeUntil

Subject<Boolean> stopSubject = PublishSubject.create();
disposable = Flowable
            .interval(INITIAL_DELAY, POLLING_INTERVAL, TimeUnit.MILLISECONDS)
            .takeUntil(stopSubject.asObservable())
            .map(x -> originationRepo.checkApplicationStatus(applicationStatusRequest))
            .take(POLL_COUNT) //YES
            .subscribe(
                response -> {
                    //update UI
                    boolean shouldStop = ... // calculate
                    if (shouldStop) {
                        stopSubject.onNext(true);
                    }
                }
            ...
             )

附言。这是伪代码。我希望你能明白。