TrueMVP

public interface PhotosContract {

    interface Model {
        ...
        List<Photo> photos();
    }

    interface View {
        void onPhotosAdded();
        ...
    }

    interface Presenter {
        ...
        List<Photo> photos();

        void onPhotosLoaded();
        ...
    }
}

...

interface PhotoDataSource {
    List<Photo> photos();
}

public class PhotoAdapter extends RecyclerView.Adapter<PhotoAdapter.PhotoHolder> {
    ...

    private PhotoDataSource dataSource;

    public PhotoAdapter(PhotoDataSource dataSource) {
        this.dataSource = dataSource;
    }

    private List<Photo> getPhotos() {
        return dataSource.photos();
    }

    ...

    @Override
    public void onBindViewHolder(@NonNull final PhotoHolder holder, int position) {
        ...
        Photo photo = getPhotos().get(position);
        ...
    }

    @Override
    public int getItemCount() {
        return getPhotos().size();
    }

    ...
}

public class WPFragment extends Fragment implements PhotosContract.View {
    ...

    @Nullable
    @Override
    public View onCreateView(
        @NonNull LayoutInflater inflater,
        @Nullable ViewGroup container,
        @Nullable Bundle savedInstanceState
    ) {
        ...
        adapter = new PhotoAdapter(new PhotoDataSource() {
            @Override
            List<Photo> photos() {
                return presenter.photos();
            }
        });
        return view;
    }

    ...

    @Override
    public void onPhotosAdded() {
        adapter.notifyDataSetChanged();
    }

    ...
}

...

public class PhotosPresenter implements PhotosContract.Presenter {

    ...

    @Override
    public void onPhotosLoaded() {
        if (viewExists()) {
            view.get().onPhotosAdded();
            isLoading = false;
        }
    }

    @Override
    public List<Photo> photos() {
        return model.photos();
    }

}

...


public class UnsplashService implements PhotosContract.Model {

    private List<Photo> photos = new ArrayList<>();

    @Override
    public void loadPhotos(int page) {
        Call<List<Photo>> call = photosEndPoint.getPhotos(USER_ID, page, ORIENTATION, ORDER);
        Log.d(TAG, "REQUEST: " + call.request().toString());
        call.enqueue(new Callback<List<Photo>>() {
            @Override
            public void onResponse(Call<List<Photo>> call, Response<List<Photo>> response) {
                if (response.isSuccessful()) {
                    photos.addAll(response.body());
                    presenter.onPhotosLoaded();
                } else {
                    presenter.onLoadFailure();
                }
            }

            @Override
            public void onFailure(Call<List<Photo>> call, Throwable t) {
                presenter.onLoadFailure();
            }
        });
    }

    @Override
    public List<Photo> photos() {
        return this.photos;
    }

}