ViewModel LiveData in android not working

Question

I just learned about liveata viewmodel. I have an object, the main_activity consists of 2 fragments, in which when I change the value of ControlFragment, the value on DetailFragment will change. But It not work , while I change the value in fragment control, the value in fragment 2 does not change.

Please, help me fix issue

ViewModelMedal

public class ViewModelMedal extends ViewModel {
public MutableLiveData<Integer> numberGold = new MutableLiveData<>();
public MutableLiveData<Integer> numberSilver = new MutableLiveData<>();
public MutableLiveData<Integer> numberBronze = new MutableLiveData<>();

public ViewModelMedal() {
    numberGold.setValue(0);
    numberSilver.setValue(0);
    numberBronze.setValue(0);
}

}

ControlFragment.java

public class ControlFragmentJava extends Fragment implements View.OnClickListener {
private Button btnGold, btnGoldPlus, btnSilver, btnSilverPlus, btnCu, btnCuPlus;
private TextView tvGold, tvSilver, tvBronze;
private ViewModelMedal mViewModelMedal;

@Nullable
@Override
public View onCreateView(@NonNull LayoutInflater inflater, @Nullable ViewGroup container, @Nullable Bundle savedInstanceState) {
    View view = inflater.inflate(R.layout.fragment_control, container, false);
    mViewModelMedal = ViewModelProviders.of(this).get(ViewModelMedal.class);

    .
    .
    .

    return view;
}

@Override
public void onClick(View v) {
    switch (v.getId()) {
        case R.id.btnBronzePlus:
            mViewModelMedal.numberCBronze.setValue(mViewModelMedal.numberCu.getValue()+1);
            initSetData();
            break;
        case R.id.btnBronzeMinus:
            mViewModelMedal.numberBronze.setValue(mViewModelMedal.numberCu.getValue()-1);
            initSetData();
            break;
        case R.id.btnGoldMinus:
            mViewModelMedal.numberGold.setValue(mViewModelMedal.numberGold.getValue()-1);
            initSetData();
            break;
        case R.id.btnGoldPlus:
            mViewModelMedal.numberGold.setValue(mViewModelMedal.numberGold.getValue()+1);
            initSetData();
            break;
        case R.id.btnSilverMinus:
            mViewModelMedal.numberSilver.setValue(mViewModelMedal.numberSilver.getValue()-1);
            initSetData();
            break;
        case R.id.btnSilverPlus:
            mViewModelMedal.numberSilver.setValue(mViewModelMedal.numberSilver.getValue()+1);
            initSetData();
            break;

    }

}

}

DetailFragment

public class DetailFragment extends Fragment {
public ViewModelMedal mViewModelMedal;
private TextView tvGold, tvSilver, tvBronze;


@Nullable
@Override
public View onCreateView(@NonNull LayoutInflater inflater, @Nullable ViewGroup container, @Nullable Bundle savedInstanceState) {
    View view = inflater.inflate(R.layout.fragment_detail,container,false);
    tvBronze = view.findViewById(R.id.tvDetailBronzeNumber);
    tvGold = view.findViewById(R.id.tvDetailGoldNumber);
    tvSilver = view.findViewById(R.id.tvDetailSilverNumber);
    mViewModelMedal = ViewModelProviders.of(this).get(ViewModelMedal.class);
    mViewModelMedal.numberBronze.observe(this, new Observer<Integer>() {
        @Override
        public void onChanged(Integer integer) {
            tvCu.setText(String.valueOf(mViewModelMedal.numberCu.getValue()));
        }
    });
    mViewModelMedal.numberGold.observe(this, new Observer<Integer>() {
        @Override
        public void onChanged(Integer integer) {
            tvGold.setText(String.valueOf(mViewModelMedal.numberGold.getValue()));
        }
    });
    mViewModelMedal.numberSilver.observe(this, new Observer<Integer>() {
        @Override
        public void onChanged(Integer integer) {
            tvSilver.setText(String.valueOf(mViewModelMedal.numberSilver.getValue()));
        }
    });
    return view;
}

Answer 1

The issue is pretty simple here: you have two instances of the ViewModelMedal class as you use the two fragments as the ViewModelStoreOwner in the ViewModelProviders.of(this) calls. What might help you is using the parent Activity to manage the view model by calling ViewModelProviders.of(requireActivity()) .

Note that the ViewModelProviders class is deprecated as stated by the message on its page:

This class is deprecated.

Use the constructors for ViewModelProvider directly.