Why isn't my fragments onSaveInstanceState() b

I have a fragment which has its own state (selected buttons, etc). That state is lost on a screen rotation.

The activity that contains the fragment has a portrait layout in /res/layout/, and an almost identical landscape layout in /res/layout-land/. Both layouts include the fragment like so:

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="fill_parent"
    android:layout_height="fill_parent">
    <fragment
        android:id="@+id/testFragment"
        android:layout_width="fill_parent"
        android:layout_height="wrap_content"
        class="au.com.x.y.TestFragment" />
...</LinearLayout>

The fragment class I've been testing with is:

public class TestFragment extends android.support.v4.app.Fragment {
    private static final String TAG = "TestFragment";
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        Log.i(TAG, "onCreate(): " + 
                (savedInstanceState != null ? "NOT NULL" : "NULL"));
    }
    public void onActivityCreated(Bundle savedInstanceState) {
        super.onActivityCreated(savedInstanceState);
        Log.i(TAG, "onActivityCreated(): " + 
                (savedInstanceState != null ? "NOT NULL" : "NULL"));
    }
    public void onSaveInstanceState(Bundle state) {
        super.onSaveInstanceState(state);
        Log.i(TAG, "onSaveInstanceState()");
        state.putString("saved_thing", "some_value");
    }
    public View onCreateView(
        LayoutInflater inflater,
        ViewGroup container,
        Bundle b) { ... }
}

Note that I'm using the pre-3.0 support package for fragments, brought in through ActionBarSherlock.

LogCat gives me:

BEFORE SCREEN ROTATION (PORTRAIT):
02-23 11:45:58.015: I/TestFragment(22629): onCreate(): NULL
02-23 11:45:58.015: I/TestFragment(22629): onCreateView()
02-23 11:45:58.035: I/TestFragment(22629): onActivityCreated(): NULL
AFTER SCREEN ROTATION (LANDSCAPE):
02-23 11:46:00.615: I/TestFragment(22629): onCreate(): NULL
02-23 11:46:00.615: I/TestFragment(22629): onCreateView()
02-23 11:46:00.635: I/TestFragment(22629): onActivityCreated(): NULL

As you can see, onSaveInstanceState() is never called, and the fragment always gets a null savedInstanceState, in both onCreate() and onActivityCreated().

I've tried myFragment.setRetainInstance(true) in my activities onCreate(), but that hasn't changed anything.

My onSaveInstanceState() has an @Override, so I know it's not something stupid like a typo.

I've looked at one of the ActionBarSherlock examples (com.actionbarsherlock.sample.shakespeare) and the fragments there are having their onSaveInstanceState() methods called properly. As far as I can tell, that example is written exactly how my code is — fragments included through both a layout and a layout-land XML. I've even built that sample using exactly the same version of ActionBarSherlock as my main project is using, and saving the instance state works fine for that example.

How do I retain my fragments state across screen rotations? Why isn't onSaveInstanceState() being called?

回答1:

You can enable myFragment.setRetainInstance(true) to retain the state, but it does this 'automatically', i.e. it retains the values assigned to your class members and does NOT use the onSaveInstanceState (and hence savedInstanceState is always null).

Make sure the FragmentActivity that hosts this fragment does not override onSaveInstanceState or when it does it should call super.onSaveInstanceState(Bundle).

回答2:

If the fragment needs a different layout resource when rotated, setRetainInstance(true) cannot be used. This page shows the lifecycle of fragment with setRetainInstance(true).

Original idea is use onSaveInstanceState() to retain all members data, just like a regular Activity. However, for some reason, onSaveInstanceState() is not get called. But FragmentActivity is correct, as @Eric Kok suggested). The best solution I found is to use Arguments of Fragment.

See the solution by Fyodor Volchyok, it is simple. Just work as if the outState in onSaveInstanceState(), and savedInstanceState in onViewCreated().