无法连接到位置管理器android

Question

public class locationservice extends Service implements LocationListener

{
     boolean isGPSEnabled = false;

        boolean isNetworkEnabled = false;
protected Context mContext;
        boolean canGetLocation = false;
        protected LocationManager locationManager;
        Location location;
        double latitude;
        double longitude;
       @Override
       public IBinder onBind(Intent arg0) {
          return null;
       }
       public locationservice() {
            //this.mContext = context;
            getLocation();
        }
       @Override
       public int onStartCommand(Intent intent, int flags, int startId) {

           new start().execute();
           scheduleNextUpdate();
          return START_STICKY;
       }

       @Override
       public void onDestroy() {
          super.onDestroy();
          Toast.makeText(this, "Service Destroyed", Toast.LENGTH_LONG).show();
       }
       private void scheduleNextUpdate()
        {
          Intent intent = new Intent(this, this.getClass());
          PendingIntent pendingIntent =
              PendingIntent.getService(this, 0, intent, PendingIntent.FLAG_UPDATE_CURRENT);

          // The update frequency should often be user configurable.  This is not.

          long currentTimeMillis = System.currentTimeMillis();
          long nextUpdateTimeMillis = currentTimeMillis + 1* DateUtils.MINUTE_IN_MILLIS;
          Time nextUpdateTime = new Time();
          nextUpdateTime.set(nextUpdateTimeMillis);

         /* if (nextUpdateTime.hour < 8 || nextUpdateTime.hour >= 18)
          {
            nextUpdateTime.hour = 8;
            nextUpdateTime.minute = 0;
            nextUpdateTime.second = 0;
            nextUpdateTimeMillis = nextUpdateTime.toMillis(false) + DateUtils.DAY_IN_MILLIS;
          }*/
         AlarmManager alarmManager = (AlarmManager)getSystemService(Context.ALARM_SERVICE);
          alarmManager.set(AlarmManager.RTC, nextUpdateTimeMillis, pendingIntent);
        }


public void getLocation()
{

   try
    {
        locationManager = (LocationManager)getSystemService(LOCATION_SERVICE);

        //getting GPS status
        isGPSEnabled = locationManager.isProviderEnabled(LocationManager.GPS_PROVIDER);

        //getting network status
        isNetworkEnabled = locationManager.isProviderEnabled(LocationManager.NETWORK_PROVIDER);

        if (!isGPSEnabled && !isNetworkEnabled)
        {
            // no network provider is enabled
        }
        else
        {
            this.canGetLocation = true;

            //First get location from Network Provider
            if (isNetworkEnabled)
            {
                locationManager.requestLocationUpdates(
                        LocationManager.NETWORK_PROVIDER,
                        0,
                        0, (android.location.LocationListener) this);

                Log.d("Network", "Network");

                if (locationManager != null)
                {
                    location = locationManager.getLastKnownLocation(LocationManager.NETWORK_PROVIDER);
                    updateGPSCoordinates();
                }
            }


            if (isGPSEnabled)
            {
                if (location == null)
                {
                    locationManager.requestLocationUpdates(
                            LocationManager.GPS_PROVIDER,
                        0,
                          0, (android.location.LocationListener) this);

                    Log.d("GPS Enabled", "GPS Enabled");

                    if (locationManager != null)
                    {
                        location = locationManager.getLastKnownLocation(LocationManager.GPS_PROVIDER);
                        updateGPSCoordinates();
                    }
                }
            }
        }
    }
    catch (Exception e)
    {
        //e.printStackTrace();
        Log.e("Error : Location", "Impossible to connect to LocationManager", e);
    }


}

public void updateGPSCoordinates()
{
    if (location != null)
    {
        latitude = location.getLatitude();
        longitude = location.getLongitude();
    }
}


public double getLatitude()
{
    if (location != null)
    {
        latitude = location.getLatitude();
    }

    return latitude;
}


public double getLongitude()
{
    if (location != null)
    {
        longitude = location.getLongitude();
    }

    return longitude;
}



class start extends AsyncTask<String, Void,String> {

    private Exception exception;
    protected void onPreExecute() {

    }
    protected String doInBackground(String... urls) {

          try {
                // open a connection to the site
                URL url = new URL("http://192.168.1.2/mylocation/update_location.php");
                URLConnection con = url.openConnection();
                // activate the output
                con.setDoOutput(true);
                PrintStream ps = new PrintStream(con.getOutputStream());
                // send your parameters to your site
                ps.print("latlong="+latitude+"$"+longitude);
                ps.print("&mobile=7803214029");

                // we have to get the input stream in order to actually send the request
                con.getInputStream();

                // close the print stream
                ps.close();
                } catch (MalformedURLException e) {
                    e.printStackTrace();
                } catch (IOException e) {
                    e.printStackTrace();
                }






        return null;
    }

    protected void onPostExecute() {
        // TODO: check this.exception 
        // TODO: do something with the feed
    }

}



@Override
public void onLocationChanged(Location location) {
    // TODO Auto-generated method stub

}

}

我试图从服务中获取经度和纬度，但我得到一个空指针表达式，它还说无法连接到位置manager.at android.content.ContextWrapper.getSystemService（ContextWrapper.java:526）