observable ScrollListener

caller.java

        subscription = scrollManager.getScrollObservable()
                .distinctUntilChanged()
                .subscribe(new Subscriber<Integer>() {
                    @Override
                    public void onCompleted() {

                    }

                    @Override
                    public void onError(Throwable e) {

                    }

                    @Override
                    public void onNext(Integer totalCount) {
                        fetchNextPage();
                    }
                });

RecyclerViewScrollManager.java

public class RecyclerViewScrollManager {

    //region Variables
    private int totalItemCount;
    private int lastVisibleItem;
    private final int visibleThreshold;
    private final PublishRelay<Integer> relay;
    private RecyclerView recyclerView;
    @Nullable private RecyclerView.OnScrollListener scrollListener;
    //endregion

    public RecyclerViewScrollManager(@NonNull RecyclerView recyclerView, int visibleThreshold) {
        this.visibleThreshold = visibleThreshold;
        this.recyclerView = recyclerView;
        this.scrollListener = buildOnScrollListener((LinearLayoutManager) recyclerView.getLayoutManager());
        this.recyclerView.addOnScrollListener(scrollListener);
        relay = PublishRelay.create();
    }

    @NonNull
    public PublishRelay<Integer> getScrollObservable() {
        return relay;
    }

    @NonNull
    private RecyclerView.OnScrollListener buildOnScrollListener(final LinearLayoutManager layoutManager) {
        return new RecyclerView.OnScrollListener() {
            @Override
            public void onScrollStateChanged(RecyclerView recyclerView, int newState) {
                super.onScrollStateChanged(recyclerView, newState);
            }

            @Override
            public void onScrolled(RecyclerView recyclerView, int dx, int dy) {
                super.onScrolled(recyclerView, dx, dy);
                totalItemCount = layoutManager.getItemCount();
                lastVisibleItem = layoutManager.findLastVisibleItemPosition();
                if (totalItemCount <= (lastVisibleItem + visibleThreshold)) {
                    relay.call(totalItemCount);
                }
            }
        };
    }

    public void dispose() {
        if (scrollListener != null) {
            recyclerView.removeOnScrollListener(scrollListener);
        }

        recyclerView = null;
    }
}