Where Fragment save its State when FragmentTransac

Question

Backgroud: i have a menu on the left, and different scrollable contents on the right. i wanted to save the scrolled position. But i failed. Then ...

I have set up a very simple project to test it.

In words, i have a menu on the left, and different contents all holding an <EditText> on the right. (of the same class though, they are of different instances)

In codes, (very simple)

content.xml

<EditText xmlns:android="http://schemas.android.com/apk/res/android"
    android:id="@+id/text"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:hint="Please save my text ..." />

ContentFragment.java

package ... import ...

public class ContentFragment extends Fragment {
    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
        return inflater.inflate(R.layout.content, container, false);
    }

    @Override
    public void onSaveInstanceState(Bundle outState) {
        super.onSaveInstanceState(outState);
        System.out.println("Why this is NOT called ?");
        Log.v("onSaveInstanceState()", "outState = " + outState);
    }
}

and the program generated MenuFragment.java

package ... import ...

public class MenuFragment extends ListFragment {
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setListAdapter(new ArrayAdapter<String>(getActivity(), android.R.layout.simple_list_item_1, new String[]{"Item 1", "Item 2", "Item 3"}));
    }
    @Override
    public void onListItemClick(ListView l, View v, int position, long id) {
        ((MainActivity) getActivity()).click();
    }
}

Lastly, our MainActivity.java

package ... import ...

public class MainActivity extends FragmentActivity {

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

        if (savedInstanceState == null)
            getSupportFragmentManager().beginTransaction()
                    .add(R.id.menu, new MenuFragment()).commit();
    }
    public void click() {
        getSupportFragmentManager().beginTransaction()
                .replace(R.id.content, new ContentFragment()  // everytime load a new instance
                ).addToBackStack(null).commit();
    }
    @Override
    protected void onSaveInstanceState(Bundle outState) {
        super.onSaveInstanceState(outState);
        System.out.println("... and this is NOT called neither :-/");
        Log.v("onSaveInstanceState()", "outState = " + outState);
    }
}

To test it, please DO NOT rotate your device.

First, choose an item from the menu, then type something in the textbox. Then choose another item and type something again. Repeat for a few times. Then navigate back and ...

you will find your texts previously typed ARE SAVED !!!

It is not surprised that the texts are saved ...

But it is surprised the texts are saved with all the onSaveInstanceState() functions NOT called.

When did Android save them while replaced by FragmentTransaction?

If i want to additionally save some data into each Fragment instance (like the scroll position), where should i put my codes?

Answer 1

By default, Edittext save their own instance. See Yalla T.'s answer.

How to retain EditText data on orientation change?