<@U0KBF8D7V> who then subscribes?

# rx

[ursus]

@Paul Woitaschek who then subscribes?

[Ulrik Bech Hald]

@ursus for that use case, I would normally return a Disposable from the method. And let the caller decide the lifespan/scope of that subscription. That makes it a lot more manageable imho.

[ursus]

sounds reasonable, what about object that needs to relay output of a cold observable to hot one?

something like this?

public class AppVisibilityManager {

    private final BehaviorRelay<Boolean> inForegroundRelay = BehaviorRelay.create();

    public AppVisibilityManager(Application application) {
        checkNotNull(application);

        application.registerActivityLifecycleCallbacks(new AppVisibilityLifecycleObserver() {
            @Override public void onAppVisibilityChanged(boolean inForeground) {
                inForegroundRelay.accept(inForeground);
            }
        });
    }

    public Observable<Boolean> inForegroundObservable() {
        return inForegroundRelay.distinctUntilChanged();
    }
}

[ursus]

or would you lazy create that cold one and make it hot via operators?

[Ulrik Bech Hald]

I would probably subscribe to the inForegroundObservable() upon Application.onCreate. Or call a

fun bind() : Observable<Boolean>

that returns a memoized Observable instance of

inForegroundRelay.distinctUntilChanged().share()

(or whatever publish()/replay() variant you need.

Not sure how this relates to the kotlin rx channel though?

[ursus]

right, but then its up to callee to sub to it to start it, i somehow dont like the coldness in this case ... i dont think rx relates to kotlin anyhow

[Ulrik Bech Hald]

Since the subscription in this case most likely is scoped to the application/process lifespan, you could just subscribe to the observable in the AppVisibilityManager ctor and instantiate it at an appropriate spot, like application.onCreate. But I just find it much more implicit (and more difficult to test) than exposing a bind() method (that should have returned ```Disposable```above, I mistyped)

[ursus]

yea you are right, and also you are being subscribe on some random thread which DI chooses since it calls the ctors

[ursus]

which is in practise almost always mainthread but you never know