Observable which does not pass anything in onNext()

Question

I would need an Observable, for example to provide a system clock, which does not need to pass anything in onNext(). I couldn\'t find a signature that would allow me to do that.

Answer 1

You don't need to call onNext if your Observable doesn't emit anything. You could use Void in your signature and do something like

Observable o = Observable.create(new Observable.OnSubscribe() {
    @Override
    public void call(Subscriber subscriber) {
        // Do the work and call onCompleted when you done,
        // no need to call onNext if you have nothing to emit
        subscriber.onCompleted();
    }
});

o.subscribe(new OnCompletedObserver() {
    @Override
    public void onCompleted() {
        System.out.println("onCompleted");
    }

    @Override
    public void onError(Throwable e) {
        System.out.println("onError " + e.getMessage());
    }
});

You can define an OnCompletedObserver to simplify your Observer callback so that you don't have to override the onNext since you don't need it.

public abstract class OnCompletedObserver implements Observer {
    @Override
    public void onNext(T o) {

    }
}

If I've understood what you're asking then this should do the trick.