Polling to Backend API in regular interval for certain number of times in a regular interval - Retrofit & RxJava

问题

I am looking to poll the backend call for certain number of times for a predefined regular intervals. I would like to exit the loop if I have received an expected payload in between the loop and update the UI else terminate the polling.

Below is the code I normally do when I make standard http call.

//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);

But I am kind of lost here in the following code with the syntax error and I am not able to use the same disposableSingleObserver when calling from the Flowable.interval and need help with my use case where I need to update the UI the status regularly until the time is elapsed or status is active which ever happens first and also I am not after terminating the polling if I received HTTP Status Code of 500 instead repeat until the mentioned conditions are met.

 //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);

Appreciate your help in advance.

回答1:

(in continuation with MyDogTom's answer you could also "short-circuit" the observable by throwing a custom Error/Exception)

Option 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))

回答2:

Option #1 Use 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)

Option #2 Use 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);
                    }
                }
            ...
             )

PS. This is pseudo code. I hope you get idea.

来源：https://stackoverflow.com/questions/44920829/polling-to-backend-api-in-regular-interval-for-certain-number-of-times-in-a-regu