Work with fragments with transfer data

Dog.java

public class Dog implements Serializable {

    private String name;


    public Dog(String name) {
        this.name = name;
    }

    public String getName() {
        return name;
    }
}

FragmentA.java

public class FragmentA extends Fragment {

    private static final int LAYOUT = R.layout.fragment_a;


    public static FragmentA newInstance() {
        Bundle args = new Bundle();

        FragmentA fragment = new FragmentA();
        fragment.setArguments(args);
        return fragment;
    }

    @NonNull
    @Override
    public View onCreateView(@NonNull LayoutInflater inflater,
                             @Nullable ViewGroup container,
                             @Nullable Bundle savedInstanceState) {

        final View view = inflater.inflate(LAYOUT, container, false);

        final Button btnOpenFragmenrB = view.findViewById(R.id.btn_open_fragment_b);

        btnOpenFragmenrB.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                FragmentActivity fragmentActivity = getActivity();
                if (fragmentActivity == null) {
                    return;
                }

                Navigator navigator = (Navigator) fragmentActivity;

                Dog dog = new Dog("Yana");
                navigator.openBScreen(dog);
            }
        });

        return view;
    }
}

FragmentB.java

public class FragmentB extends Fragment {

    private static final String EXTRA_DOG = "dog_key";

    private static final int LAYOUT = R.layout.fragment_b;

    public static FragmentB newInstance(Dog dog) {

        Bundle args = new Bundle();
        args.putSerializable(EXTRA_DOG, dog);

        FragmentB fragment = new FragmentB();
        fragment.setArguments(args);
        return fragment;
    }

    @NonNull
    @Override
    public View onCreateView(@NonNull LayoutInflater inflater,
                             @Nullable ViewGroup container,
                             @Nullable Bundle savedInstanceState) {

        final View view = inflater.inflate(LAYOUT, container, false);

        final Bundle arguments = getArguments();

        final TextView tvDogName = view.findViewById(R.id.tv_dog_name);

        if (arguments != null) {

            Dog dog = (Dog) arguments.getSerializable(EXTRA_DOG);
            if (dog != null) {
                String name = dog.getName();
                tvDogName.setText(name);
            }
        }


        return view;
    }
}

MainActivity.java

public class MainActivity extends AppCompatActivity implements Navigator{

    private static final String FRAGMENT_B_KEY = "Fragment_b_key";

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        openFirstScreen();
    }

    public void openFirstScreen() {
        FragmentManager fragmentManager = getSupportFragmentManager();
        fragmentManager.beginTransaction()
                .replace(android.R.id.content, FragmentA.newInstance())
                .commit();
    }


    @Override
    public void openBScreen(@NonNull Dog dog) {
        FragmentManager fragmentManager = getSupportFragmentManager();
        fragmentManager.beginTransaction()
                .replace(android.R.id.content, FragmentB.newInstance(dog))
                .addToBackStack(FRAGMENT_B_KEY)
                .commit();
    }
}

Navigator.java

public interface Navigator {

    void openBScreen(@NonNull Dog dog);
}

To pass data from an Activity to a Fragment using ViewModel in Java, you can follow these steps:

Step1 : Create a ViewModel class for sharing data between the Activity and the Fragment.

public class MyViewModel extends ViewModel {
private MutableLiveData myData = new MutableLiveData<>();

public void setData(String data) {
    myData.setValue(data);
}

public LiveData<String> getData() {
    return myData;
}

}

Step2 : In the Activity, create an instance of the ViewModel and set the data using the setData() method.

MyViewModel myViewModel = new ViewModelProvider(this).get(MyViewModel.class);
myViewModel.setData("Hello from Activity!");

Step3 : In the Fragment, get an instance of the ViewModel and observe the data using the getData() method.

MyViewModel myViewModel = new ViewModelProvider(requireActivity()).get(MyViewModel.class);
myViewModel.getData().observe(getViewLifecycleOwner(), new Observer() {
@OverRide
public void onChanged(@nullable String data) {
// update UI with the new data
}
});