Reactive Programming with RxJava/

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Reactive Everything: Multicasting

Reactive Everything: Multicasting

Learn how to share the same underlying source with multiple observers.

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Using .publish()

The simplest mechanism to convert a given cold Observable to a hot Observable is by using the method .publish(). Calling .publish() returns a ConnectableObservable, which is a special type of Observable wherein each Observer shares the same underlying resource. In other words, using .publish(), we are able to multicast, or share to multiple observers.

Subscribing to a ConnectableObservable, however, does not begin emitting items.

Java
ConnectableObservable<Integer> observable = Observable.create(source -> {
    Log.d(TAG, "Inside subscribe()");
    for (int i = 0; i < 10; i++) {
        source.onNext(i);
    }
    source.onComplete();
}).subscribeOn(Schedulers.io()).publish();
observable.subscribe(i -> {
    // This will never be called
    Log.d(TAG, "Observer 1: " + i);
});
observable.subscribe(i -> {
    // This will never be called
    Log.d(TAG, "Observer 2: " + i);
});

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