Question

This is my first Android App. I’m trying to call a function in a service from a different class i am using foursquare API. I tried this function earlier in an activity and it worked perfectly but in a service im getting a NullPointerException.
This is the code i am using:

public class GuideMeService extends Service implements LocationListener {

LocationManager locationManager;
Geocoder geocoder;
// private CalendarContentResolver Calendar;
public FoursquareApp mFsqApp;
public ArrayList<FsqVenue> mNearbyList;
private static String TAG = "Service Class";
double lat;
double lng;
public static final String[] FIELDS = { CalendarContract.Calendars.NAME,
        CalendarContract.Calendars.CALENDAR_DISPLAY_NAME,
        CalendarContract.Calendars.CALENDAR_COLOR,
        CalendarContract.Calendars.VISIBLE };

public static ArrayList<String> Events = new ArrayList<String>();
public static final Uri CALENDAR_URI = Uri
        .parse("content://com.android.calendar/calendars");
public static final Uri EVENTS_URI = Uri
        .parse("content://com.android.calendar/events");
private static final long MINIMUM_DISTANCE_CHANGE_FOR_UPDATES = 1; // in Meters
private static final long MINIMUM_TIME_BETWEEN_UPDATES = 1000; // in  Milliseconds
public static String query = "";

Set<String> calendars = new HashSet<String>();

@Override
public IBinder onBind(Intent arg0) {
    return null;
}

@Override
public void onStart(Intent intent, int startId) {
    super.onStart(intent, startId); 
    Log.d(TAG, "GuideMe Servise started");
    //this.stopSelf();
    locationManager = (LocationManager)this.getSystemService(LOCATION_SERVICE);
    locationManager.requestLocationUpdates(
            LocationManager.GPS_PROVIDER,
            MINIMUM_TIME_BETWEEN_UPDATES,
            MINIMUM_DISTANCE_CHANGE_FOR_UPDATES,
            new MyLocationListener()
            );

    Events = readCalendarEvent(getApplicationContext());
    for(int i = 0 ; i < Events.size() ; i++){
        query += Events.toArray()[i].toString() + " ";
    }
    Thread thread = new Thread()
    {
          @Override
          public void run() {

                try {
                        Location location = locationManager.getLastKnownLocation(LocationManager.GPS_PROVIDER);
                        mNearbyList = mFsqApp.SearchBykeyword(location.getLatitude(), location.getLongitude(), query);
                    }catch (Exception e) {
                        e.printStackTrace();
                    }
          }
  };

thread.start();

}

Im getting The error on this line :

mNearbyList = mFsqApp.SearchBykeyword(location.getLatitude(), location.getLongitude(), query);

And this is the function i’m calling in the mFsqApp class:

public ArrayList<FsqVenue> SearchBykeyword(double latitude, double longitude, String query) throws Exception {
    ArrayList<FsqVenue> venueList = new ArrayList<FsqVenue>();
    try {
        String ll   = String.valueOf(latitude) + "," + String.valueOf(longitude);
        URL url     = new URL(API_URL + "/venues/search?ll=" + ll + "&query=" + query + "&radius=" + 50 + "&oauth_token=" + mAccessToken + "&v=20120610");

        Log.d(TAG, "Opening URL " + url.toString());

        HttpURLConnection urlConnection = (HttpURLConnection) url.openConnection();

        urlConnection.setRequestMethod("GET");
        urlConnection.setDoInput(true);
        //urlConnection.setDoOutput(true);

        urlConnection.connect();
        String response     = streamToString(urlConnection.getInputStream());
        JSONObject jsonObj  = (JSONObject) new JSONTokener(response).nextValue();

        JSONArray groups    = (JSONArray) jsonObj.getJSONObject("response").getJSONArray("groups");

        int length          = groups.length();
        if (length > 0) {
            for (int i = 0; i < length; i++) {
                JSONObject group    = (JSONObject) groups.get(i);
                JSONArray items     = (JSONArray) group.getJSONArray("items");

                int ilength         = items.length();

                for (int j = 0; j < ilength; j++) {
                    JSONObject item = (JSONObject) items.get(j);

                    FsqVenue venue  = new FsqVenue();

                    venue.id        = item.getString("id");
                    venue.name      = item.getString("name");

                    JSONObject location = (JSONObject) item.getJSONObject("location");

                    Location loc    = new Location(LocationManager.GPS_PROVIDER);

                    loc.setLatitude(Double.valueOf(location.getString("lat")));
                    loc.setLongitude(Double.valueOf(location.getString("lng")));

                    venue.location  = loc;
                    //venue.address = location.getString("address");
                    venue.distance  = location.getInt("distance");
                    //venue.herenow = item.getJSONObject("hereNow").getInt("count");
                    venue.type      = group.getString("type");

                    venueList.add(venue);
                }
            }
        }
    } catch (Exception ex) {
        throw ex;
    }
    return venueList;
}

Updates:

07-08 21:26:18.580: W/System.err(24365): java.lang.NullPointerException
07-08 21:26:18.580: W/System.err(24365):    at com.android.guideme.GuideMeService$1.run(GuideMeService.java:86)

Answer 1

You’re declaring the (unfortunately public) mFsqApp variable here:

public FoursquareApp mFsqApp;

but you haven’t shown any code to assign it a value – so it will have the default value of null, causing a NullPointerException when you dereference it. You need to assign a non-null value to it before you dereference it, e.g. with

mFsqApp = new FoursquareApp();

… or using a value passed in elsewhere (e.g. to the constructor). It’s hard to tell which of those is appropriate in this case, but something has to assign a non-null value to it. You say similar code worked earlier in an activity – so look back at that code and see where the value was coming from there.

(Then improve your code to avoid public variables, avoid static variables where possible, avoid catching Exception, avoid just continuing in the face of an exception unless you’re really handled it etc.)