I would like to display a sortable list of restaurants. It worked when I was using a simple LiveData, but I get a NullPointerException since I changed it for a mediatorLiveData.
In the fragment, i use these lines to observe the mediatorLiveData
vm.getAllRestaurantsWithOrderMediatorLD().observe(getViewLifecycleOwner(), listRestaurants -> {
datas.clear();
datas.addAll(listRestaurants);
adapter.notifyDataSetChanged();
});
And here the viewmodel class :
public class ListRestaurantsViewModel extends ViewModel {
private final RestaurantRepository restaurantRepository;
private final SortRepository sortRepository;
private final MutableLiveData<List<RestaurantViewState>> allRestaurantsViewStateLD = new MutableLiveData<>();
private final MutableLiveData<SortRepository.OrderBy> orderLiveData = new MutableLiveData<>();
private final MediatorLiveData<List<RestaurantViewState>> allRestaurantsWithOrderMediatorLD;
Context ctx;
public ListRestaurantsViewModel(RestaurantRepository restaurantRepository, SortRepository sortRepository, Context ctx) {
this.ctx = ctx;
this.restaurantRepository = restaurantRepository;
this.sortRepository = sortRepository;
allRestaurantsWithOrderMediatorLD = new MediatorLiveData<>();
allRestaurantsWithOrderMediatorLD.addSource(getAllRestaurantsViewStateLD(), value -> allRestaurantsWithOrderMediatorLD.setValue(value));
allRestaurantsWithOrderMediatorLD.addSource(getOrderLiveData(), order -> {
List<RestaurantViewState> restaurants = getAllRestaurantsViewStateLD().getValue();
if (restaurants != null && !restaurants.isEmpty()) {
List<RestaurantViewState> newList = new ArrayList<>();
if (order == SortRepository.OrderBy.DISTANCE)
newList =
Stream.of(restaurants).sorted((a, b) -> a.getDistance() - b.getDistance()).toList();
else if (order == SortRepository.OrderBy.RATING)
newList = Stream.of(restaurants).sorted((a, b) -> Double.compare(a.getStarsCount(),
b.getStarsCount())).toList();
allRestaurantsWithOrderMediatorLD.setValue(newList);
}
}
);
}
public MediatorLiveData<List<RestaurantViewState>> getAllRestaurantsWithOrderMediatorLD() {
return allRestaurantsWithOrderMediatorLD;
}
public LiveData<SortRepository.OrderBy> getOrderLiveData() {
return sortRepository.getOrderLiveData();
}
public LiveData<List<RestaurantViewState>> getAllRestaurantsViewStateLD() {
return Transformations.map(restaurantRepository.getRestaurantsLiveData(), restaurantsList -> {
List<RestaurantViewState> restaurantViewStates = new ArrayList<>();
for (Restaurant r : restaurantsList) {
restaurantViewStates.add(new RestaurantViewState(
r.getId(),
r.getName(),
r.getType(),
r.getAdress(),
r.getImage()
)
);
}
return restaurantViewStates;
});
}
This is the error, I get
java.lang.NullPointerException: Attempt to invoke virtual method 'void androidx.lifecycle.LiveData.observeForever(androidx.lifecycle.Observer)' on a null object reference
I have no error if I observe the livedata getAllRestaurantsViewStateLD() in the fragment, so I think I did not get something in the use of mediatorLiveData Do you see what it is?