How can I subscribe and unsubscribe using onResume() and onPause() methods with RxJava 2?

Well, I need to bind emitting to my activity's lifecycle. How can I do that? And when should I create observer and observable instances?

If you have an observable that you want data from sometimes and not at other times, there is a simple way to subscribe and unsubscribe using the switchMap() operator.

Let's say you have an observable that want data from:

Observable<LocationData> locationDataObservable;

Then, if you introduce a switching observable:

PublishSubject<Boolean> switchObservable = PublishSubject.create();

you can control the subscriptions to the first observable:

Observable<LocationData> switchedLocationDataObservable =
  switchObservable
    .switchMap( abled -> abled ? locationDataObservable : Observable.never() )
    .subscribe();

To enable receiving the data, perform

switchObservable.onNext( Boolean.TRUE );

and to disable,

switchObservable.onNext( Boolean.FALSE );

The switchMap() operator takes care of subscribing and unsubscribing for you.