HasRxBusEvent.java

//Implement this interface in classes that can handle events
public interface HasRxBusEvent {
    void onEvent(RxBusEvent event);
}

RxBus.java

import java.util.ArrayList;

import javax.inject.Inject;
import javax.inject.Singleton;

import rx.Observable;
import rx.android.schedulers.AndroidSchedulers;
import rx.functions.Action1;


import rx.subjects.PublishSubject;
import rx.subjects.SerializedSubject;
import rx.subjects.Subject;

@Singleton
public class RxBus {

    boolean isStarted = false;
    private ArrayList<HasRxBusEvent> handlers = new ArrayList<>();

    @Inject
    public RxBus() {
        toObservable().observeOn(AndroidSchedulers.mainThread()).subscribe(new Action1<RxBusEvent>() {
            @Override
            public void call(RxBusEvent rxBusEvent) {
                if (isStarted) {
                    notifyHandlers(rxBusEvent);
                }
            }
        });
    }

    private final Subject<RxBusEvent, RxBusEvent> _bus = new SerializedSubject<>(PublishSubject.<RxBusEvent>create());

    public void send(RxBusEvent o) {
        _bus.onNext(o);
    }

    public Observable<RxBusEvent> toObservable() {
        return _bus;
    }

    public boolean hasObservers() {
        return _bus.hasObservers();
    }

    public void unsubscribe(final HasRxBusEvent handler) {
        handlers.remove(handler);
        if (handlers.size() == 0) {
            stop();
        }
    }

    public void subscribe(final HasRxBusEvent handler) {
        if (handlers.contains(handler)) {
            return;
        }

        handlers.add(handler);
        if (handlers.size() > 0) {
            start();
        }
    }

    public boolean hasSubscription(final HasRxBusEvent handler) {
        return handlers.contains(handler);
    }

    private void notifyHandlers(RxBusEvent event) {
        if (handlers.size() != 0) {
            for (HasRxBusEvent handler : handlers) {
                handler.onEvent(event);
            }
        }
    }

    private void stop() {
        isStarted = false;
    }

    private void start() {
        isStarted = true;
    }
}

RxBusEvent.java

//Extend this base class for events
public class RxBusEvent {
}