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Reactive Programming with RxJava

Schedulers with Operators

Explore the role of Schedulers in RxJava to control where Observables operate. Learn how the subscribeOn operator designates the thread for Observable execution and how observeOn ensures emissions are handled on the desired thread, including the Android main thread, to prevent UI thread exceptions and enable smooth multithreading in reactive Android applications.

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.subscribeOn()

The .subscribeOn() operator is used in the Observable chain to dictate where the Observable should operate–for example, the function inside of .create(). Rewriting the previous example using a Scheduler instead gives us:

Java
Observable<Integer> integerObservable = Observable.create(source -> {
    Log.d(TAG, "In subscribe");
    source.onNext(1);
    source.onNext(2);
    source.onNext(3);
    source.onComplete();
});
Log.d(TAG, "Created Observable");
Log.d(TAG, "Subscribing to Observable");
integerObservable.subscribeOn(Schedulers.newThread())
                 .subscribe(i -> Log.e(TAG, "In onNext(): " + i));
Log.d(TAG, "Finished");

Running the above code is similar to using a Thread in that the operations inside .create() now occurs in a separate thread provided by Schedulers.newThread(). The benefit of this approach over using a Thread is that tacking on a Scheduler to specify where the Observable should execute is declarative. We no longer have to worry about the ...