Communication between nested fragments in Android

Question

I recently learned how to make nested fragments in Android. I don\'t know how communication is supposed to happen, though.

From reading the fragment commun

Answer 1

Using ViewModel to communicate between nested Fragments

With pieces of the old ViewModel and LiveData now deprecated. I would like to provide information on this process as it currently stands.

In this example I am using a the predefined TabLayout that can be selected when one creates a project.

Here I have a TextView in the parent fragment -- tab, with an EditText and a Button in the child fragment -- custom layout. It passes the text entered in the child fragment to the field in the parent fragment.

I hope this helps someone.

ViewModel Class

public class FragViewModel extends ViewModel {
  private MutableLiveData digit = new MutableLiveData<>();

  public void insertDigit(CharSequence inDigit){
      digit.setValue(inDigit);
  }

  public LiveData getDigit(){
      return digit;
  }
}

This is, for the most part, verbatim from the Android Developers ViewModel Overview with a small variable name change. The Overview was used as a guide for the parent and child code below.

The Parent Fragement Code

public class Tab0Main extends Fragment {

private FragViewModel model0;

// This is the Child Fragment.
private ChildFrag childFrag;

private TextView textView;

@Nullable
@Override
public View onCreateView(@NonNull LayoutInflater inflater, @Nullable ViewGroup container, @Nullable Bundle savedInstanceState) {
    View view = inflater.inflate(R.layout.tab0_main, container, false);

    // Setup the text field.
    textView = view.findViewById(R.id.tab0TextView);

    // Inserting the Child Fragment into the FrameLayout.
    childFrag = new ChildFrag();
    FragmentTransaction transaction = getChildFragmentManager().beginTransaction();
    transaction.add(R.id.tab0Frame, childFrag).commit();

    return view;
}


@Override
public void onViewCreated(@NonNull View view, @Nullable Bundle savedInstanceState) {
    super.onViewCreated(view, savedInstanceState);

    model0 = new ViewModelProvider(getActivity()).get(FragViewModel.class);
    model0.getDigit().observe(getViewLifecycleOwner(), new Observer() {
        @Override
        public void onChanged(CharSequence charSequence) {
            textView.setText(charSequence);
        }
    });
}

The Child Fragment Code

public class ChildFrag extends Fragment {

private EditText fragEditText;
private Button fragButton;

// The ViewModel declaration
FragViewModel model;

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

    // The ViewModel Instantiation
    model = new ViewModelProvider(getActivity()).get(FragViewModel.class);

    fragEditText = view.findViewById(R.id.fragEditText);
    fragButton = view.findViewById(R.id.fragButton);
    fragButton.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {
            CharSequence in = fragEditText.getText();
            // Inserting a digit into the ViewModel carrier.
            model.insertDigit(in);
        }
    });
    return view;
  }
}