Rx Java Observable execute until some condition

问题

I am trying to find a way to execute observable until some condition is met.

Consider the following example:

 myDelayedObservable = createListenerObserver();
    public Observable<Boolean> createListenerObserver() {

      // The part I am looking for
    }

    ViewTreeObserver.OnGlobalLayoutListener listenerLayout = new ViewTreeObserver.OnGlobalLayoutListener() {
        @Override
        public void onGlobalLayout() {
           myDelayedObservable.onCompleted();
         getTargetView().getViewTreeObserver().removeGlobalOnLayoutListener(this);

        }
    };

    public void performMultipleRequests() {

        Observable<Boolean> longRunningTask = Observable.zip(oneRequest, anotherRequest, myDelayedObservable,...);

    }

So the idea is to run multiple requests, for instance a download request, together with myDelayedObservable using zip, so longRunningTask completes only when all requests plus listener (in my case view finished layout) are completed.

But the problem is, I cannot find the right way to create my Observable for listener. It is like a barrier, so pseudo code

while(!viewIsLaidOut) {
  // just wait
}
observable.complete();
// After that `longRunningTask` should be completed

Please suggest the right way to achieve this, I have thought about Future, Callable but this seems to not be the best solution to me.

回答1:

1) You need to map all observables to the same type, eg. Observable<Boolean>, so you can merge them:

observable1.map(String s -> "...".equals(s))
observable2.map(Integer i -> i > 0 && i < 100)
observable3.map(MyClass m -> true)
...

2) Use Observable.merge() to merge them all into single stream. Using zip for this purpose will only work if all observables emit the same number of items, otherwise it will complete as soon as the first one completes, without waiting for the rest.

Observable<Boolean> allInOne = Observable.merge(observable1, observable2, ...);

3) myDelayedObservable is just one of those observables that shall hold allInOne incomplete until some listener calls back. Use Subject for this purpose:

Subject<Boolean> myDelayedObservable = PublishSubject.create();

4) When your listener is ready, call myDelayedObservable.onComplete().

5) Subscribe to allInOne and react on completion:

allInOne.subscribe(b -> { ... }, e -> { ... },
    () -> { ... go ahead with your next task ... });

回答2:

Try with:

PublishSubject<Boolean> myDelayedObservable = PublishSubject.create<>();

or for RxJava2

 PublishProcessor<Boolean> myDelayedObservable = PublishProcessor.create<>();

And when ready just call

 myDelayedObservable.onNext(true)
 //not this, myDelayedObservable.onComplete();

来源：https://stackoverflow.com/questions/41856356/rx-java-observable-execute-until-some-condition

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java

android

promise

rx-java

future