RxJava - observe data that might always change

Question

I'm trying to jump on the reactive bandwagon, but after reading and going through lots of examples, I still haven't found what I'm looking for.

I have a model object which might get change during any time in the lifecycle of the application.
The changes might come from a specific request to update it (from servers, db, etc) or it might get updated due an event which fires in the app.

My question is how do I create an Observable of such an object and how do I keep updating the subscribers when there's a change?

From what I've seen so far I can create the observable like so:

Observable.create(new Observable.OnSubscribe<MyModel>() {
    @Override
    public void call(final Subscriber<? super MyModel> subscriber) {
        subscriber.onNext(MyModel instance);
    }
});

What I'm missing here:

1. I do not want to emit different values (instances of MyModel) but just want to let the subscribers know that the same instance (the one on which they subscribed on) has changed.

2. If I understand it right, then the call method is invoked whenever a new subscriber has registered, but that's not what I need, I need to take action only when there's an update and then I want to notify ALL subscribers.

There's a good chance that I just got this all wrong, which is why I'd be happy to understand how it's possible to accomplish my needs with RxJava.

Thanks.

Answer 1

I think the best option to do stuff like that is Subjects. So you can have something like this:

public static class MyModel {
    private PublishSubject<MyModel> changeObservable = PublishSubject.create();
    private String field1;

    public String getField1() {
        return field1;
    }

    public void setField1(String field1) {
        this.field1 = field1;
        changeObservable.onNext(this);
    }

    public Observable<MyModel> getModelChanges() {
        return changeObservable;
    }

    @Override
    public String toString() {
        return "MyModel{" +
                "field1='" + field1 + '\'' +
                '}';
    }
}


public static void main(String[] args) {
    MyModel myModel = new MyModel();
    myModel.getModelChanges()
            .subscribe(System.out::println);

    myModel.setField1("1");
    myModel.setField1("2");
    myModel.setField1("3");
}

So all setters in the model will notify that something has changed in your model and all subscribers will get that data.