joao86 joao86 - 2 months ago 22
Android Question

LiveData is not updating its value after first call

I have been beating my head against the wall and I cannot understand why this is happening. I am working with the new Architectural Components for Android and I am having problems updating a LiveData with a List of Objects.
I have two spinners. When i change the option in the first one, The second one must have its content changed. But this last part is not happening.
Can anyone help me?

State.java

@Entity(tableName = "states")
public class State{

@PrimaryKey(autoGenerate = false)
private int id;

private String name;

@ColumnInfo(name = "countryId")
private String CountryId;

@Ignore
private Object geoCenter, geoLimit;

public State(){

}

public int getId() {
return id;
}

public void setId(int id) {
this.id = id;
}

public String getName() {
return name;
}

public void setName(String name) {
this.name = name;
}

public String getCountryId() {
return CountryId;
}

public void setCountryId(String countryId) {
CountryId = countryId;
}
}


StateDAO

@Dao
public interface StateDao {

@Query("SELECT * FROM states")
LiveData<List<State>> getAllStates();

@Query("SELECT * FROM states WHERE countryId = :countryID")
LiveData<List<State>> getStatesFromCountry(String countryID);

@Query("SELECT COUNT(*) FROM states")
int getNrStates();

@Query("SELECT COUNT(*) FROM states WHERE countryId = :countryID")
int getNrStatesByCountry(String countryID);

@Insert(onConflict = IGNORE)
void insertAll(List<State> states);

@Delete
void delete(State state);
}


StateRepository

@Singleton
public class StatesRepository {

private final WebServices services;
private final StateDao stateDao;
private final Executor executor;

@Inject
public StatesRepository(Executor executor, StateDao stateDao, WebServices services) {
this.services = services;
this.stateDao = stateDao;
this.executor = executor;
}


public LiveData<List<State>> getStates(String token){
refreshStates(token);

return stateDao.getAllStates();
}

public LiveData<List<State>> getStatesFromCountry(String countryID){

return stateDao.getStatesFromCountry(countryID);
}

private void refreshStates(final String token){

executor.execute(() -> {

Log.d("oooooo", stateDao.getNrStates() + "");
if(stateDao.getNrStates() == 0){

try {
Response<List<State>> response = services.getStates("Bearer "+token).execute();

stateDao.insertAll(response.body());

} catch (IOException e) {
e.printStackTrace();
}
}
});
}
}


StateViewModel

public class StatesViewModel extends ViewModel {

private LiveData<List<State>> states;
private StatesRepository repo;

@Inject
public StatesViewModel(StatesRepository repository){

this.repo = repository;
}

public void init(String token){

states = repo.getStates(token);
}

public void getStatesFromCountry(String countryID){

states = repo.getStatesFromCountry(countryID);

}

public LiveData<List<State>> getStates(){

return this.states;
}

}


Fragment

public class EditAddressFragment extends LifecycleFragment implements View.OnClickListener, Injectable{


private Spinner country, city, state, zip_code;
private String token;
private List<Country> countries;
private List<City> cities;
private List<State> states;
@Inject ViewModelFactory viewModelFactory;


@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
View view = inflater.inflate(R.layout.addresses_edit_layout, container, false);

city = view.findViewById(R.id.city);
state = view.findViewById(R.id.state);
country = view.findViewById(R.id.country);
...

countries = new ArrayList<>();
cities = new ArrayList<>();
states = new ArrayList<>();

return view;
}


@Override
public void onActivityCreated(Bundle savedInstanceState) {
super.onActivityCreated(savedInstanceState);


CountrySpinnerAdapter adapter = new CountrySpinnerAdapter(getActivity(), android.R.layout.simple_spinner_item, countries);
country.setAdapter(adapter);

CitySpinnerAdapter cityAdapter = new CitySpinnerAdapter(getActivity(), android.R.layout.simple_spinner_item, cities);
city.setAdapter(cityAdapter);
StateSpinnerAdapter stateAdapter = new StateSpinnerAdapter(getActivity(), android.R.layout.simple_spinner_item, states);
state.setAdapter(stateAdapter);


CountriesViewModel countriesViewModel = ViewModelProviders.of(this, viewModelFactory).get(CountriesViewModel.class);
countriesViewModel.init(token);
countriesViewModel.getCountries().observe(this, adapter::setValues);

CityViewModel cityViewModel = ViewModelProviders.of(this, viewModelFactory).get(CityViewModel.class);
cityViewModel.init(token);
cityViewModel.getCities().observe(this, cityAdapter::setValues);

StatesViewModel statesViewModel = ViewModelProviders.of(this, viewModelFactory).get(StatesViewModel.class);
statesViewModel.init(token);
statesViewModel.getStates().observe(this, states -> {
Log.d("called", states.toString());
stateAdapter.setValues(states); } );


country.setOnItemSelectedListener(new AdapterView.OnItemSelectedListener() {
@Override
public void onItemSelected(AdapterView<?> adapterView, View view, int i, long l) {

Country c = (Country) adapterView.getItemAtPosition(i);

Log.d("cd", c.getId());

//states = new ArrayList<State>();

statesViewModel.getStatesFromCountry(c.getId());

}

@Override
public void onNothingSelected(AdapterView<?> adapterView) {

}
});


....

Adapter

public void setValues(List<State> states)
{
this.states = states;
Log.d("s", states.isEmpty()+" "+states.toString());
notifyDataSetChanged();
}

Answer Source

Well, I have reached a solution for this issue and found out how this LiveData things works.

Thanks to @MartinMarconcini for all his help is debugging ;)

So apparently, the observers are linked to the object you first set it up to. You cannot replace the object (by attribution) or otherwise it will not work. Also, if the value of your variable is going to change then you should use MutableLiveData

So the change necessary were:

1. Change from LiveData to MutableLiveData and pass that MutableLiveData to the repository when you need to update it

public class StatesViewModel extends ViewModel {

private MutableLiveData<List<State>> states; ;;CHANGED
private StatesRepository repo;

@Inject
public StatesViewModel(StatesRepository repository){
    this.repo = repository;
}


public void init(String token){

    states = repo.getStates(token);
}

public void getStatesFromCountry(String countryID){

    repo.getStatesFromCountry(this.states, countryID); ;;CHANGED
}

public LiveData<List<State>> getStates(){

    return this.states;
}
}

2. In the repository, update the MutableLiveData using setValue

@Singleton
public class StatesRepository {

private final WebServices services;
private final StateDao stateDao;
private final Executor executor;

@Inject
public StatesRepository(Executor executor, StateDao stateDao, WebServices services) {
    this.services = services;
    this.stateDao = stateDao;
    this.executor = executor;
}


public MutableLiveData<List<State>> getStates(String token){
    refreshStates(token);

    final MutableLiveData<List<State>> data = new MutableLiveData<>();

    data.setValue(stateDao.getAllStates());

    return data;

}

;; CHANGED
public void getStatesFromCountry(MutableLiveData states, final String countryID){

    states.setValue(stateDao.getStatesFromCountry(countryID));

}

private void refreshStates(final String token){

    executor.execute(() -> {

        if(stateDao.getNrStates() == 0){

            try {
                Response<List<State>> response = services.getStates("Bearer "+token).execute();

                stateDao.insertAll(response.body());

            } catch (IOException e) {
                e.printStackTrace();
            }
        }
    });
}
}

3. Changed the DAO to return List instead of LiveData>

@Dao
public interface StateDao {

@Query("SELECT * FROM states")
List<State> getAllStates();

@Query("SELECT * FROM states WHERE ctrId = :countryID")
List<State> getStatesFromCountry(String countryID);

@Query("SELECT COUNT(*) FROM states")
int getNrStates();

@Query("SELECT COUNT(*) FROM states WHERE ctrId = :countryID")
int getNrStatesByCountry(String countryID);

@Insert(onConflict = IGNORE)
void insertAll(List<State> states);

@Delete
void delete(State state);
}

4.Finally allow to perform queries in the main thread

AppModule.java

@Singleton @Provides
AppDatabase provideDb(Application app) {
    return Room.databaseBuilder(app, AppDatabase.class,"unitail.db")
            .allowMainThreadQueries()
            .fallbackToDestructiveMigration()
            .build();
}