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.

Sure, I could use any object and then pass null, but that doesn't make much sense. So my question is if there is a better way to do that.

Observable.create(new Observable.OnSubscribe<Anyobject>() { // use any object in the signature              @Override public void call(Subscriber<? super Anyobject> subscriber) {                      subscriber.onNext(null); // then pass null                     subscriber.onCompleted();              }          }) 

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<Void> o = Observable.create(new Observable.OnSubscribe<Void>() {     @Override     public void call(Subscriber<? super Void> 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<Void>() {     @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<T> implements Observer<T> {     @Override     public void onNext(T o) {      } } 

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