Why is onChanged() not called when observing LiveData

Question

This question is a follow up to this problem here: How to make retrofit API call using ViewModel and LiveData

The mistakes 1 and 2 highlighted in that post's response have been fixed. For mistake 3, I haven't yet moved the API call to a repository, but I will once the code start working properly.

So I'm trying to make an API call using Retrofit, using MVVM with LiveData and ViewModel. The API call (which currently is in the ViewModel), is working properly, but the changes is not being picked up by the Observer in the Activity.

I've setup my ViewModel observer as follow:

public class PopularGamesActivity extends AppCompatActivity {


private static final String igdbBaseUrl = "https://api-endpoint.igdb.com/";
private static final String FIELDS = "id,name,genres,cover,popularity";
private static final String ORDER = "popularity:desc";
private static final int LIMIT = 30;

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_popular_games);

    PopularGamesViewModel popViewModel = ViewModelProviders.of(this).get(PopularGamesViewModel.class);
    popViewModel.getGameList().observe(this, new Observer<List<Game>>() {
        @Override
        public void onChanged(@Nullable List<Game> gameList) {
            String firstName = gameList.get(0).getName();
            Timber.d(firstName);
        }

And my ViewModel code is as follow:

public class PopularGamesViewModel extends AndroidViewModel {

private static final String igdbBaseUrl = "https://api-endpoint.igdb.com/";
private static final String FIELDS = "id,name,genres,cover,popularity";
private static final String ORDER = "popularity:desc";
private static final int LIMIT = 30;


public PopularGamesViewModel(@NonNull Application application) {
    super(application);

}

public LiveData<List<Game>> getGameList() {
    final MutableLiveData<List<Game>> gameList = new MutableLiveData<>();

    // Create the retrofit builder
    Retrofit.Builder builder = new Retrofit.Builder()
            .baseUrl(igdbBaseUrl)
            .addConverterFactory(GsonConverterFactory.create());

    // Build retrofit
    Retrofit retrofit = builder.build();

    // Create the retrofit client
    RetrofitClient client = retrofit.create(RetrofitClient.class);
    Call<List<Game>> call = client.getGame(FIELDS,
            ORDER,
            LIMIT);

    call.enqueue(new Callback<List<Game>>() {
        @Override
        public void onResponse(Call<List<Game>> call, Response<List<Game>> response) {
            Timber.d("api call sucesss");
            if (response.body() != null) {
                Timber.d("First game: " + response.body().get(0).getName());

                gameList.setValue(response.body());
            }
        }

        @Override
        public void onFailure(Call<List<Game>> call, Throwable t) {
            Timber.d("api call failed");
        }
    });

    return gameList;
}

}

When I run the code, the onResponse in the ViewModel class will output the correct response from the API call, so the call is working properly. But the onChanged() in the PopularGamesActivity class will never get called. Can someone shed some light on what I'm doing wrong? Thank you!

Answer 1

Ok, so this turned out to be a weird android studio bug. I was initially running the code on my real nexus 4 device, and the onChange never gets called. However, after running it on an emulated device, it started working immediately. And now, it's working on my real device too.

I don't know the actual reason behind it, but if anyone in the future run into a problem where onChange won't get called, try switching device/emulators.

Cheers.