Acquiring GPS location fix

GPS has opened a Pandora's box for mobile developer. There has been a huge influx of such application ranging from tracking apps to location based social networking apps.

Many of today's applications require us to get a GPS fix on the location of the device when the application is being used.

Therefore without further ado lets get into some coding.

The following snippet of codes employ a service and a broadcast receiver to get onto a location fix. It gets the most recent fix on the location and then closes the GPS updates as soon as it gets a fix.

public class FindGPSActivity extends Activity{

Intent myGpsService;

MainGpsReciever gpsReciever;

final String GPS_FILTER = "MyGPSLocation";  

protected void onCreate(Bundle savedInstanceState) {

// TODO Auto-generated method stub

super.onCreate(savedInstanceState);

setContentView(R.layout.textlayout);

                initGpsListeners()

}

- initGpsListeners method initializes the necessary services and the recievers. 

private void initGpsListeners() {

           

            myGpsService = new Intent(this, GpsService.class);

            startService(myGpsService);

            String GPS_FILTER = getResources().getString(GPS_FILTER);

            IntentFilter mainFilter = new IntentFilter(GPS_FILTER);

            gpsReciever = new MainGpsReciever();

            registerReceiver(gpsReciever, mainFilter);

           

      }

- this is where i get my location data which i can further use in my activity.

This receiver is called from within the service which is actually looking for a GPS location. A GPS location fix is an unreliable bit of information and we cannot be sure when we might get it. it can range anywhere from 5 seconds to 5 minutes or if you are inside a huge structure like a building you might never get it unless you come out. Therefore we use a service because we do not want our location finder to be garbage collected by android.

private class MainGpsReciever extends BroadcastReceiver {

             public void onReceive(Context arg0, Intent calledIntent) {

                       

                   Constants.GPSLatitude = calledIntent.getDoubleExtra("latitude", -1);

                   Constants.GPSLongitude = calledIntent.getDoubleExtra("longitude", -1);

                   Constants.GPSSpeed = calledIntent.getFloatExtra("speed", -1);

                       

                   Log.i("GPS Demo", "Lat & Long --- "+Constants.GPSLatitude+"--"+Constants.GPSLongitude);

                   Log.i("GPS Demo", Speed --- "+Constants.GPSSpeed);

//               

                                         

             }

       }

}

This is the service class in its entirety. 

public class GpsService extends Service {

      String GPS_FILTER = "";

      Thread triggerService;

      LocationManager lm;

      GpsListener gpsLocationListener;

      boolean isRunning = true;

     

      @Override

      public void onCreate() {

           

            // TODO Auto-generated method stub

            super.onCreate();

            GPS_FILTER = “MyGPSLocation”;

           

      }

     

      @Override

      public void onStart(Intent intent, int startId) {

            // TODO Auto-generated method stub

            super.onStart(intent, startId);          

            triggerService = new Thread(new Runnable(){

                  public void run(){

                        try{

                              Looper.prepare();//Initialize the current thread as a looper.

                              lm = (LocationManager)getSystemService(Context.LOCATION_SERVICE);

                              gpsLocationListener = new GpsListener();

                              long minTime = 30000; // 5 sec...

                              float minDistance = 10;

                              lm.requestLocationUpdates(LocationManager.GPS_PROVIDER, minTime,

                                          minDistance, gpsLocationListener);

                              Looper.loop();

                        }catch(Exception ex){

                              System.out.println("Exception in triggerService Thread -- "+ex);

                        }

                  }

            }, "myLocationThread");

            triggerService.start();

      }

     

      @Override

      public void onDestroy() {

            // TODO Auto-generated method stub

            super.onDestroy();

            removeGpsListener();

      }

     

      @Override

      public IBinder onBind(Intent intent) {

            // TODO Auto-generated method stub

            return null;

      }

     

      private void removeGpsListener(){

            try{

                  lm.removeUpdates(gpsLocationListener);

            }

            catch(Exception ex){

                  System.out.println("Exception in GPSService --- "+ex);

            }

      }

     

      class GpsListener implements LocationListener{

            public void onLocationChanged(Location location) {

                  // TODO Auto-generated method stub

                  double latitude = location.getLatitude();

                  double longitude = location.getLongitude();

                  float speed = location.getSpeed();

                  Intent filterRes = new Intent(GPS_FILTER);

                  filterRes.putExtra("latitude", latitude);

                  filterRes.putExtra("longitude", longitude);

                  filterRes.putExtra("speed", speed);

                  sendBroadcast(filterRes);

            }

            public void onProviderDisabled(String provider) {

                  // TODO Auto-generated method stub

                 

            }

            public void onProviderEnabled(String provider) {

                  // TODO Auto-generated method stub

                 

            }

            public void onStatusChanged(String provider, int status, Bundle extras) {

                  // TODO Auto-generated method stub

                 

            }

      }

}