Fallback Observable for RxJava

Question

I\'m in search for a better way to achieve a simple Observable fallback system for empty results when using RxJava. The idea is that, if a local query for a set of data results

Answer 1

Use switchIfEmpty operator.

There is example of usage:

Observable.create(new Observable.OnSubscribe() {
    @Override
    public void call(Subscriber subscriber) {
        // return no item
        //subscriber.onNext(...);
        System.out.println("Generating nothing :)");
        subscriber.onCompleted();
    }
}).switchIfEmpty(Observable.create(new Observable.OnSubscribe() {
    @Override
    public void call(Subscriber subscriber) {
        System.out.println("Generating item");
        subscriber.onNext("item");
        subscriber.onCompleted();
    }
})).subscribe(new Observer() {
    @Override
    public void onCompleted() {
        System.out.println("onCompleted");
    }

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

    @Override
    public void onNext(String s) {
        System.out.println("onNext: " + s);
    }
});

Simplified with lamdas:

Observable.create(subscriber -> {
    // return no item
    //subscriber.onNext(...);
    System.out.println("Generating nothing :)");
    subscriber.onCompleted();
}).switchIfEmpty(Observable.create(subscriber -> {
    System.out.println("Generating item");
    subscriber.onNext("item");
    subscriber.onCompleted();
})).subscribe(
    s -> System.out.println("onNext: " + s),
    throwable -> System.out.println("onError"),
    () -> System.out.println("onCompleted")
);