如何使用androidx从另一个片段调用片段方法

Question

I am using androidx jetpack navigation component in my application and I am confused on how to call a method in previous fragment from the current fragment.

There is currently no resource online on how to do this.

My implementation is below...

FRAGMENT A

This is the code sample of the first fragment.

public class FragmentOne extends Fragment{

    private String holder;

    private NavController navController;
    private Button btn_next;

    private void findViews(View view){
        btn_next = view.findViewById(R.id.btn_next);
    }

    @Override
    public void onCreate(@Nullable Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
    }

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

    return view;

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

        navController = Navigation.findNavController(view);
        findViews(view);

        holder = "VALUE IN HOLDER VARIABLE";

        btn_next.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {

                navController.navigate(R.id.action_fundone_to_fragmenttwo);
            }
        });


    }

    public void executeInFragmentTwo(){
        System.out.println(holder);
        Toast.makeText(getContext(), holder, Toast.LENGTH_LONG).show();
    }

}

FRAGMENT TWO

This is the code sample of the second fragment

public class FragmentTwo extends Fragment{

    private NavController navController;
    private Button btn_exec_fragment_one_method;

    private void findViews(View view){
        btn_exec_fragment_one_method= view.findViewById(R.id.btn_exec_fragment_one_method);
    }

    @Override
    public void onCreate(@Nullable Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
    }

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

    return view;

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

        navController = Navigation.findNavController(view);
        findViews(view);

        btn_exec_fragment_one_method.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {

                //HOW DO I CALL FRAGMENT ONE METHOD FROM HERE

                //The method with name "executeInFragmentTwo"

            }
        });
    }

}

Please any help on this would really be appreciated.

Answer 1

Your first fragment will not be in a resumed state when the user is onto the second fragment.

If you need a function to be executed from another screen/fragment then you probably need to move this function to a ViewModel that is either tied to the lifecycle of the graph that these screens/fragments are part of or to the host activity lifecycle so that you get the same instance in both screens/fragments.

To inject a model that lives as long as your graph you use the following syntax:

private val model: MyViewModel by navGraphViewModels(R.id.myGraph) { ViewModelFactory() }