How can I create a BehaviorSubject that subscribes to an observable?

Question

I have a function which should return a BehaviorSubject. The subject is meant to return the most current version of a Profile

(user)Profile is just a POJO that contains references to three members:
- a User,
- that User's MeasurementList,
- and a Deadline.

Two of these properties is obtained via a retrofit call, and one of them is already held in a class variable.

Whenever the observable emits a new measurement list or deadline, the BehaviorSubject should emit a new updated Profile.

Here is a (hopefully helpful) diagram of what should be happening

This is what I have so far

 public BehaviorSubject<Profile> observeProfile() {

        if (profileBS == null) {

            profileBS = BehaviorSubject.create();

            Observable o = Observable.combineLatest(
                    Observable.just(userAccount),
                    observeMeasurements(),
                    observeDeadline(),
                    Profile::new
            );


            profileBS.subscribeTo(o); //subscribeTo does not exist, but this is what I am trying to figure out how to do.

        }
        return profileBS;
    }

Can anyone help me to create this BehaviorSubject properly?

Thanks.

Answer 1

Subject implements the Observer interface so you can do the following

public BehaviorSubject<Profile> observeProfile() {

        if (profileBS == null) {

            profileBS = BehaviorSubject.create();

            Observable o = Observable.combineLatest(
                    Observable.just(userAccount),
                    observeMeasurements(),
                    observeDeadline(),
                    Profile::new
            );

            // Note the following returns a subscription. If you want to prevent leaks you need some way of unsubscribing.
            o.subscribe(profileBS); 

        }
        return profileBS;
}

Note that you should come up with a way of handling the resulting subscription.