RxJava as event bus is called multiple times even when only once triggered

Question

I am trying to implement the RxJava event bus, where my use case is to get triggered when subscribed and when the event is sent. But with my code even when I send the event once, I am receiving multiple events. It is working fine for the first time, it is behaving weirdly from the second time I login into my application. i.e; For the first time desired code implemented once, for the second time it implemented two time and so on.

public class RxBus {

    public RxBus() {
    }

    private PublishSubject<String> bus = PublishSubject.create();

    public void send(String str) {
        bus.onNext(str);
    }

    public Observable<String> toObservable() {
        return bus;
    }

}

The code to subscribe RxBus is below:

public void sendEvents(){
        rxBus.send("Trigger event");
    }

 public void startListener(){
        rxBus.toObservable().subscribe(str -> {
           //do action//This is executing multiple lines
        });
    }

In the above code, even though when the sendEvents() is executed once the line containing "do action" is executing multiple times. So, is something I am doing wrong here. When I went through some blogs they are asking to unsubscribe the subscription when we visit that screen a second time. But how can I unsubscribe from that?

Help here is greatly appreciated!

You have to remember the `Disposable` your `subscribe` returns and dispose it when the context of `startListener` is exited (e.g., in `onDestroy`). — akarnokd, Jun 10 '21 at 06:17

Dominik Setniewski · Accepted Answer · 2021-06-10T13:42:44.993

Easy solution is to declare a field:

SerialDisposable busDisposable = new SerialDisposable();

Modify you startListener method:

public void startListener() {
    busDisposable.set(rxBus.toObservable().subscribe(str -> {
        // ...
    }));
}

In that way, when you add new subscription the previous one will be disposed, so you will end up with only one subcription at a time. This is good if your startListener call is not determined by the lifecycle. (Remember to call busDisposable.dispose() when you no longer want to recieve events. )

But if you call your startListener in onResume/onStart/onCreate, you should better use Disposable instead of SerialDisposable and simply call stopListener method in onPause/onStop/onDestroy.

public void stopListener() {
    busDisposable.dispose();
}

RxJava as event bus is called multiple times even when only once triggered

1 Answers1