Unsubscribing from RxJava2/RxAndroid PublishSubject - rx-java2

Question

I'm trying to replace EventBus with RxAndroid.
I want pageable fragments to subscribe/unsubscribe to an event source, these fragments get created and discarded relatively quickly, depending on how fast the user slides to a new page.
In EventBus I was able to add an decorated callback method (ie #Subscribe(threadMode = ThreadMode.MAIN)) and register/unregister in the onStart/onStop methods of the fragment.
With RxJava2 I now create a PublishSubject object in a class
public static PublishSubject<List<Long>> m_psUpdatedDays = PublishSubject.create();
public static void publishUpdatedDays(List<Long> lDay) {
m_psUpdatedDays.onNext(lDay);
}
and subscribe to this publisher in another class by calling the following in the Fragment's onStart method:
m_psUpdatedDays.observeOn(AndroidSchedulers.mainThread()).subscribe(new Observer<List<Long>>() {
#Override public void onSubscribe(Disposable d) {}
#Override public void onNext(List<Long> longs) {
...
Update Fragment UI here
...
}
#Override public void onError(Throwable e) {}
#Override public void onComplete() {}
});
My question is how can I unsubscribe this new Observer when the Fragment's onStop method is called by the system?
Do I need to store the Disposable object which I get in the onSubscribe and then call .dispose() on it in the onStop method?

Answer 1

You can make use of a CompositeDisposable object, which can keep a list of disposables and all of them can be disposed together.
Create a CompositeDisposable instance in the base fragment level, keep on adding your disposables into it.
public abstract class BaseFragment extends Fragment {
protected CompositeDisposable mCompositeDisposable = new CompositeDisposable();
#Override
public void onPause() {
super.onPause();
mCompositeDisposable.clear();
//clear will clear all, but can accept new disposable.
// You can call it on `onPause` or `orDestroyView` events.
}
#Override
public void onDestroy() {
super.onDestroy();
mCompositeDisposable.dispose();
//dispose will clear all and set isDisposed = true, so it will not accept any new disposable
}
}
In your fragments, subscribe to the Observable using the subscribeWith method, which gives you a disposable instantly and this disposable you can dispose later in the onPause or onDestroy events (wherever you want)
public class MyFragment extends BaseFragment {
#Override
public void onStart() {
super.onStart();
Disposable disposable = m_psUpdatedDays.observeOn(AndroidSchedulers.mainThread())
.subscribeWith(new DisposableObserver<List<Long>>() { // Use `subscribeWith` instead of `subscribe`, which will give you back the disposable , which can be disposed later
#Override
public void onNext(List<Long> longs) {
// Update Fragment UI here
}
#Override
public void onError(Throwable e) {
}
#Override
public void onComplete() {
}
});
mCompositeDisposable.add(disposable); // add the disposable to the disposable list
}
}