当AsyncTask完成活动时，调用片段方法

Question

I have an app with a Navigation Drawer Activity which is calling some fragments on it.

In one of them, I have a Google Map integration, where retrieving from SharedPreferences, I show some markers and stuff.

On the Activity, I have an AsyncTask to update the data when clicking an action bar button. It takes the new data into the SharedPreferences.

I'm having trouble finding a way to call again the paintmap() method from the FragmentMap which is the one that takes the SharedPreferences data and paint the map with the new markers and so on.

I have tried OnSharedPreferenceChangeListener with no result.

Also tried getting the actual fragment with findFragmentByTag but I'm not able to call the method.

So, what's the better way to tell the fragment that the data has been updated and need to redraw the map?

Thanks in advance.

Edit 1: Some things I have tried:

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

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

    txtUpdateInfo = (TextView) view.findViewById(R.id.last_update_info);


    initilizeMap(); // This one includes paintMap at the end. It creates the map.
Check this pastebin for more: http://pastebin.com/DPPB7FiK


    SharedPreferences.OnSharedPreferenceChangeListener spChanged = new SharedPreferences.OnSharedPreferenceChangeListener() {

        @Override
        public void onSharedPreferenceChanged(
                SharedPreferences sharedPreferences, String key) {

            paintMap();
        }

    };

    return view;
}

Also tried, on MainActivity AsyncTask's postExecute, to retrieve the fragment:

FragmentManager fm = getFragmentManager();
Fragment f = fm.findFragmentByTag("MAP");

f.paintMap(); // This gives me error and I cannot compile

Also, in the same place:

 FragmentMap f = new FragmentMap();
 f.paintMap(); 

This last one compiles but gave me NullPointer to everything on the fragment... not working neither.

Answer 1

The problem with this code...

FragmentManager fm = getFragmentManager();
Fragment f = fm.findFragmentByTag("MAP");

f.paintMap(); // This gives me error and I cannot compile

...is that you've declared f as a Fragment and the Android Fragment class doesn't have a method called paintMap() . You need to declare it as FragmentMap and cast the return of findFragmentByTag as follows...

FragmentManager fm = getFragmentManager();
FragmentMap f = (FragmentMap) fm.findFragmentByTag("MAP");
f.paintMap();

The call to f.paintMap() should work then.

Also (for reference) the following will never work...

FragmentMap f = new FragmentMap();
f.paintMap(); 

The reason is that like an Activity a Fragment has a life-cycle which means it isn't fully initialised until it is used in a FragmentTransaction and has gone through its life-cycle methods such as onAttach , onCreateView , onResume etc.