MapView messed up my fragment transactions?

Issue

I have a fragment with a mapview. I can open another fragment (call it listfragment) from the action bar, it works fine. But if I rotate the screen, and then try to open the listfragment, it does not load, instead the mapview flickers on time (the map in the view goes blank and then appears again). If I try to load the listfragment again by clicking the menuitem on the action bar, the app crashes with

java.lang.IllegalStateException: Fragment already added:

Part of MainActivity that loads the fragment:

    @Override
    protected void onCreate(final Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
        setSupportActionBar(toolbar);

        mNewTrackFragment = (NewTrackFragment) getFragmentManager()
                .findFragmentByTag(TAG_NEW_TRACK_FRAGMENT);
        if (mNewTrackFragment == null) {
            mNewTrackFragment = NewTrackFragment.newInstance();
        }
        FragmentManager fragmentManager = getFragmentManager();
        fragmentManager.beginTransaction()
                .add(R.id.fragment_container, mNewTrackFragment)
                .commit();
    }

    @Override
    public boolean onOptionsItemSelected(MenuItem item) {
        int id = item.getItemId();

        if (id == R.id.action_track_list) {
            if (null == mTrackListFragment) {
                mTrackListFragment = TrackListFragment.newInstance();
            }
            FragmentManager fragmentManager = getFragmentManager();
            fragmentManager.beginTransaction()
                    .replace(R.id.fragment_container, mTrackListFragment, TAG_TRACK_LIST_FRAGMENT)
                    .addToBackStack(null)
                    .commit();

            return true;
        }

Part of NewTrackFragment with the MapView:

    public NewTrackFragment() {
}

public static NewTrackFragment newInstance() {
    NewTrackFragment fragment = new NewTrackFragment();
    return fragment;
}

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

@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
                         Bundle savedInstanceState) {
    View view = inflater.inflate(R.layout.fragment_new_track, container, false);

    mTrackTitleTV = (TextView) view.findViewById(R.id.tv_track_title);
    mDistanceTV = (TextView) view.findViewById(R.id.tv_distance);
    mElapsedTimeTV = (TextView) view.findViewById(R.id.tv_elapsed_time);
    mSpeedTV = (TextView) view.findViewById(R.id.tv_speed);
    mAscentTV = (TextView) view.findViewById(R.id.tv_ascent);
    mDescentTV = (TextView) view.findViewById(R.id.tv_descent);
    mAltitudeTV = (TextView) view.findViewById(R.id.tv_altitude);
    mStartStopFab = (FloatingActionButton) view.findViewById(R.id.fab_startstop);
    mMapView = (MapView) view.findViewById(R.id.new_track_mapview);

    setupMapView(savedInstanceState);

    return view;
}

private void setupMapView(Bundle savedInstanceState) {
    mMapView.onCreate(savedInstanceState);
    mMapView.getMapAsync(this);
}

I googled the best of the evening for some info about it but found nothing similar.

Solution

There's a couple of things wrong here. Right now, you are not passing TAG_NEW_TRACK_FRAGMENT as a tag in the call to add within onCreate. Because of this, you are adding a NewTrackFragment instance without an associated tag, and therefore the call to findFragmentByTag will always return null. Essentially, you are creating a new instance of NewTrackFragment every time you rotate the device. This is not good, because the state of the FragmentManager is preserved across device rotations, meaning it is still holding on to each Fragment you add to it. Because you are unconditionally calling add, the FragmentManager will end up holding multiple instances of NewTrackFragment.

With that said, what you should do is add the tag in the call to add and only call add once you know the FragmentManager is not currently holding on to an instance of NewTrackFragment:

mNewTrackFragment = (NewTrackFragment) getFragmentManager()
                .findFragmentByTag(TAG_NEW_TRACK_FRAGMENT);
        if (mNewTrackFragment == null) {
            mNewTrackFragment = NewTrackFragment.newInstance();
            FragmentManager fragmentManager = getFragmentManager();
            fragmentManager.beginTransaction()
                    .add(R.id.fragment_container, mNewTrackFragment, TAG_NEW_TRACK_FRAGMENT)
                    .commit();
        }

You might want to do something similar with your TrackListFragment as well:

if (id == R.id.action_track_list) {
            FragmentManager fragmentManager = getFragmentManager();
            mTrackListFragment = (TrackListFragment) fragmentManager.findFragmentByTag(TAG_TRACK_LIST_FRAGMENT);
            if (null == mTrackListFragment) {
                mTrackListFragment = TrackListFragment.newInstance();
                fragmentManager.beginTransaction()
                        .replace(R.id.fragment_container, mTrackListFragment, TAG_TRACK_LIST_FRAGMENT)
                        .addToBackStack(null)
                        .commit();
            }
}

Answered By - cascal