Retain data in Fragment switching

Question

Working on an app that included 3 fragments. I want to retain data in the FragmentA when the user decides to switch back to FragmentA from FragmentB or FragmentC via BottomNavigationView. My code works great with changing screen orientation, but for some reason it wont retain data on fragment change.

For testing, I've used only one EditText that should retain data from string.

MainActivity

public class MainActivity extends AppCompatActivity implements 
BottomNavigationView.OnNavigationItemSelectedListener {

Fragment Frag = new Fragment();

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);

    BottomNavigationView navigation = findViewById(R.id.navigation);
    navigation.setOnNavigationItemSelectedListener(this); // mOnNavigationItemSelectedListener


    if (savedInstanceState != null)
    {
        Frag = getSupportFragmentManager().getFragment(savedInstanceState, "Frag");
    }
    else
    loadFragment(new FragmentA());
}

@Override
public boolean onNavigationItemSelected(@NonNull MenuItem menuItem) {
    Fragment fragment = null;
    int i = menuItem.getItemId();
    if (i == R.id.fragmentA) {
        fragment = new FragmentA();
    } else if (i == R.id.fragmentB) {
        fragment = new FragmentB();
    } else if (i == R.id.fragmentC) {
        fragment = new FragmentC();           
    }

    return loadFragment(fragment);
}

private boolean loadFragment(Fragment fragment)
{
    if (fragment != null)
    {
        getSupportFragmentManager().beginTransaction().replace(R.id.fragment_container, fragment).commit();
        Frag = fragment;
        return true;
    }
    return false;
}

@Override
protected void onSaveInstanceState(Bundle outState) {
    super.onSaveInstanceState(outState);
    getSupportFragmentManager().putFragment(outState, "Frag", Frag);
}
}

FragmentA

public class FragmentA extends Fragment {

EditText editText;
String string;

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

    if (savedInstanceState != null)
    {
        string = savedInstanceState.getString("Text", "");
    }
}

@Nullable
@Override
public View onCreateView(@NonNull LayoutInflater inflater, @Nullable ViewGroup container, @Nullable Bundle savedInstanceState) {
    // return super.onCreateView(inflater, container, savedInstanceState);
    LayoutInflater layoutInflater = getActivity().getLayoutInflater();
    View view = layoutInflater.inflate(R.layout.fragmentA, container, false);

    editText = view.findViewById(R.id.centerText);
    editText.setText(string);
    return view;
}

@Override
public void onSaveInstanceState(@NonNull Bundle outState) {
    super.onSaveInstanceState(outState);
    string = editText.getText().toString();
    outState.putString("Text", string);
}
}

I want that editText retains data when user switches back to FragmentA from FragmentB or FragmentC. I've been struggling with this problem for some time now, trying different methods with no luck.

Answer 1

Here is your mistake

if (i == R.id.fragmentA) {
    fragment = new FragmentA();
} else if (i == R.id.fragmentB) {
    fragment = new FragmentB();
} else if (i == R.id.fragmentC) {
    fragment = new FragmentC();           
}

On click you create new fragment instance

Answer 2

Either you can keep the references to your fragments, instead of creating new ones every time like you do here:

if (i == R.id.fragmentA) {
    fragment = new FragmentA();
} else if (i == R.id.fragmentB) {
    fragment = new FragmentB();
} else if (i == R.id.fragmentC) {
    fragment = new FragmentC();           
}

You could also use a ViewPager which allows you not only to swipe in-between the screens, but to set viewPager.setOffscreenPageLimit(i); which means that fragments will not be recreated unless they're too far off screen.

Answer 3

Thank you for your replies. This is what I changed. It is now working although I'm not sure if that's the elegant way to solve this problem. Data now retains in EditText while navigating back to FragmentA.

MainActivity

public class MainActivity extends AppCompatActivity implements 
BottomNavigationView.OnNavigationItemSelectedListener {

Fragment Frag = new Fragment();
Fragment FragmentA;
Fragment FragmentB;
Fragment FragmentC;

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);

    BottomNavigationView navigation = findViewById(R.id.navigation);
    navigation.setOnNavigationItemSelectedListener(this); // mOnNavigationItemSelectedListener

    FragmentA = new FragmentA();
    FragmentB = new FragmentB();
    FragmentC = new FragmentC();

    if (savedInstanceState != null)
    {
        Frag = getSupportFragmentManager().getFragment(savedInstanceState, "Frag");
    }
    else
    loadFragment(FragmentA);
}

@Override
public boolean onNavigationItemSelected(@NonNull MenuItem menuItem) {
    Fragment fragment = null;
    int i = menuItem.getItemId();
    if (i == R.id.fragmentA) {
        fragment = FragmentA;
    } else if (i == R.id.fragmentB) {
        fragment = FragmentB;
    } else if (i == R.id.fragmentC) {
        fragment = FragmentC;
    }
    return loadFragment(fragment);
}

private boolean loadFragment(Fragment fragment)
{
    if (fragment != null)
    {
        getSupportFragmentManager().beginTransaction().hide(FragmentA).commit();
        getSupportFragmentManager().beginTransaction().replace(R.id.fragment_container, fragment).commit();
        getSupportFragmentManager().beginTransaction().show(fragment).commit();

        Frag = fragment;
        return true;
    }
    return false;
}

@Override
protected void onSaveInstanceState(Bundle outState) {
    super.onSaveInstanceState(outState);
    getSupportFragmentManager().putFragment(outState, "Frag", Frag);
}
}