Facebook Android SDK: why is the Activity recreated before calling Fragment's onActivityResult?

Question

I wrote a Fragment to manage Facebook log in/out with Facebook Android SDK 3.5.2, following the example given here.

When the login process through Facebook web widgets is done, MainActivity is started again (onCreate is called).

Then in the example code if savedInstanceState!=null in MainActivity's onCreate, the savedInstanceState is checked to know if the existing FacebookPrefsFragment instance must be restored or if a new instance must be created:

if (savedInstanceState == null) {
    // Add the fragment on initial activity setup
    mainFragment = new MainFragment();
    getSupportFragmentManager()
    .beginTransaction()
    .add(android.R.id.content, mainFragment)
    .commit();
} else {
    // Or set the fragment from restored state info
    mainFragment = (MainFragment) getSupportFragmentManager()
    .findFragmentById(android.R.id.content);
}

My problem is that my MainActivity has many Fragments, and savedInstanceState can be not null not only when on the Facebook login process. So I have two questions:

• Why is MainActivity created again after the Facebook login process? Shouldn't just FacebookPrefsFragment's onActivityResult be called?

• If it's going to be created, how can I know that it is because the Facebook SDK called it?

MainActivity

public class MainActivity extends FragmentActivity {

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

        if (savedInstanceState != null) {       

            // If the Activity has been started after the Facebook login process, restart the FacebookPrefsFragment,
            // but how can I be sure that MainActivity has been called by the Facebook app?

            FragmentTransaction fragmentTransaction = getSupportFragmentManager().beginTransaction();
            Fragment facebookPrefsFragment = new FacebookPrefsFragment();       
            fragmentTransaction.replace(R.id.content_container, facebookPrefsFragment, "facebookPrefsFragment");
            fragmentTransaction.commit();
        }
        else{
            // start other Fragment
        }
    }

    // ...
}

FacebookPrefsFragment

public class FacebookPrefsFragment extends Fragment{

    private void onSessionStateChange(Session session, SessionState state, Exception exception) {
        if (state.isOpened()) {
            Log.i(this.getClass().getSimpleName(), "Logged in", MyApplication.LOG_LEVEL);
        } else if (state.isClosed()) {
            Log.i(this.getClass().getSimpleName(), "Logged out", MyApplication.LOG_LEVEL);
        }
    }

    private Session.StatusCallback callback = new Session.StatusCallback() {
        @Override
        public void call(Session session, SessionState state, Exception exception) {
            onSessionStateChange(session, state, exception);
        }
    };

    private UiLifecycleHelper uiHelper;

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

        View view = inflater.inflate(R.layout.facebook_prefs, container, false);

        LoginButton authButton = (LoginButton) view.findViewById(R.id.authButton);
        authButton.setPublishPermissions(Arrays.asList("publish_actions"));
        authButton.setFragment(this);

        return view;
    }

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        uiHelper = new UiLifecycleHelper(getActivity(), callback);
        uiHelper.onCreate(savedInstanceState);
    }

    @Override
    public void onResume() {
        super.onResume();

        Session session = Session.getActiveSession();
        if (session != null &&
               (session.isOpened() || session.isClosed()) ) {
            onSessionStateChange(session, session.getState(), null);
        }

        uiHelper.onResume();
    }

    @Override
    public void onActivityResult(int requestCode, int resultCode, Intent data) {
        super.onActivityResult(requestCode, resultCode, data);
        uiHelper.onActivityResult(requestCode, resultCode, data);
    }

    @Override
    public void onPause() {
        super.onPause();
        uiHelper.onPause();
    }

    @Override
    public void onDestroy() {
        super.onDestroy();
        uiHelper.onDestroy();
    }

    @Override
    public void onSaveInstanceState(Bundle outState) {
        super.onSaveInstanceState(outState);
        uiHelper.onSaveInstanceState(outState);
    }
}

Answer 1

Oops, I found out why the MainActivity is recreated everytime: that's because I have the option "Don't keep activities" activated on my phone! Now I have to find out what to do in that case...