locationManager = (LocationManager) cette.getSystemService(Context.LOCATION_SERVICE); return null pointer exception

Followind code retourne toujours null poiner exception pour le directeur des lieux.

Mon GPSTracker classe
finale privée Contexte mContext;

//flag for GPS status
boolean isGPSEnabled = false;
//flag for network status
boolean isNetworkEnabled = false;
//flag for GPS status
boolean canGetLocation = false;
Location location; //location
double latitude; //latitude
double longitude; //longitude
//The minimum distance to change Updates in meters
private static final long MIN_DISTANCE_CHANGE_FOR_UPDATES = 10; //10 meters
//The minimum time between updates in milliseconds
private static final long MIN_TIME_BW_UPDATES = 1000 * 60 * 1; //1 minute
//Declaring a Location Manager
protected LocationManager locationManager;
//Location locManager = locationManager.getLastKnownLocation(LocationManager.GPS_PROVIDER);
public GPSTracker(Context context) {
this.mContext = context;
getLocation();
}
public Location getLocation() {
try {
locationManager = (LocationManager) this.getSystemService(Context.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,
MIN_TIME_BW_UPDATES,
MIN_DISTANCE_CHANGE_FOR_UPDATES, this);
Log.d("Network", "Network");
if (locationManager != null) {
location = locationManager
.getLastKnownLocation(LocationManager.NETWORK_PROVIDER);
if (location != null) {
latitude = location.getLatitude();
longitude = location.getLongitude();
}
}
}
//if GPS Enabled get lat/long using GPS Services
if (isGPSEnabled) {
if (location == null) {
locationManager.requestLocationUpdates(
LocationManager.GPS_PROVIDER,
MIN_TIME_BW_UPDATES,
MIN_DISTANCE_CHANGE_FOR_UPDATES, this);
Log.d("GPS Enabled", "GPS Enabled");
if (locationManager != null) {
location = locationManager
.getLastKnownLocation(LocationManager.GPS_PROVIDER);
if (location != null) {
latitude = location.getLatitude();
longitude = location.getLongitude();
}
}
}
}
}
} catch (Exception e) {
e.printStackTrace();
}
return location;
}
/**
* Stop using GPS listener
* Calling this function will stop using GPS in your app
* */
public void stopUsingGPS(){
if(locationManager != null){
locationManager.removeUpdates(GPSTracker.this);
}      
}
/**
* Function to get latitude
* */
public double getLatitude(){
if(location != null){
latitude = location.getLatitude();
}
//return latitude
return latitude;
}
/**
* Function to get longitude
* */
public double getLongitude(){
if(location != null){
longitude = location.getLongitude();
}
//return longitude
return longitude;
}
/**
* Function to check GPS/wifi enabled
* @return boolean
* */
public boolean canGetLocation() {
return this.canGetLocation;
}
/**
* Function to show settings alert dialog
* On pressing Settings button will lauch Settings Options
* */
public void showSettingsAlert(){
AlertDialog.Builder alertDialog = new AlertDialog.Builder(mContext);
//Setting Dialog Title
alertDialog.setTitle("GPS is settings");
//Setting Dialog Message
alertDialog.setMessage("GPS is not enabled. Do you want to go to settings menu?");
//On pressing Settings button
alertDialog.setPositiveButton("Settings", new DialogInterface.OnClickListener() {
public void onClick(DialogInterface dialog,int which) {
Intent intent = new Intent(Settings.ACTION_LOCATION_SOURCE_SETTINGS);
mContext.startActivity(intent);
}
});
//on pressing cancel button
alertDialog.setNegativeButton("Cancel", new DialogInterface.OnClickListener() {
public void onClick(DialogInterface dialog, int which) {
dialog.cancel();
}
});
//Showing Alert Message
alertDialog.show();
}
@Override
public void onLocationChanged(Location location) {
this.location = location;
}
@Override
public void onProviderDisabled(String provider) {
}
@Override
public void onProviderEnabled(String provider) {
}
@Override
public void onStatusChanged(String provider, int status, Bundle extras) {
}
@Override
public IBinder onBind(Intent arg0) {
return null;
}

Je suis en train d'appel

if(gps.isGPSEnabled){
Toast.makeText(getBaseContext(),"GPS enabled", 
Toast.LENGTH_SHORT).show();
baseurl = "http://my.careerfolio.net";
}
else{
gps.showSettingsAlert();
}

il toujours les paramètres d'affichage de l'alerte, plutôt que de toast texte, toute aide?

Mon Journal.

06-20 02:54:06.336: W/System.err(909): java.lang.NullPointerException
06-20 02:54:06.416: W/System.err(909):  at android.content.ContextWrapper.getSystemService(ContextWrapper.java:519)
06-20 02:54:06.416: W/System.err(909):  at com.incv.mobile.freejscf.GPSTracker.getLocation(GPSTracker.java:50)
06-20 02:54:06.446: W/System.err(909):  at com.incv.mobile.freejscf.GPSTracker.<init>(GPSTracker.java:44)
06-20 02:54:06.446: W/System.err(909):  at com.incv.mobile.freejscf.MyApplication.<init>(MyApplication.java:34)
06-20 02:54:06.446: W/System.err(909):  at java.lang.Class.newInstanceImpl(Native Method)
06-20 02:54:06.456: W/System.err(909):  at java.lang.Class.newInstance(Class.java:1130)
06-20 02:54:06.486: W/System.err(909):  at android.app.Instrumentation.newApplication(Instrumentation.java:990)
06-20 02:54:06.486: W/System.err(909):  at android.app.Instrumentation.newApplication(Instrumentation.java:975)
06-20 02:54:06.486: W/System.err(909):  at android.app.LoadedApk.makeApplication(LoadedApk.java:504)
06-20 02:54:06.486: W/System.err(909):  at android.app.ActivityThread.handleBindApplication(ActivityThread.java:4417)
06-20 02:54:06.486: W/System.err(909):  at android.app.ActivityThread.access$1300(ActivityThread.java:141)
06-20 02:54:06.486: W/System.err(909):  at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1316)
06-20 02:54:06.506: W/System.err(909):  at android.os.Handler.dispatchMessage(Handler.java:99)
06-20 02:54:06.506: W/System.err(909):  at android.os.Looper.loop(Looper.java:137)
06-20 02:54:06.516: W/System.err(909):  at android.app.ActivityThread.main(ActivityThread.java:5103)
06-20 02:54:06.516: W/System.err(909):  at java.lang.reflect.Method.invokeNative(Native Method)
06-20 02:54:06.516: W/System.err(909):  at java.lang.reflect.Method.invoke(Method.java:525)
06-20 02:54:06.546: W/System.err(909):  at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:737)
06-20 02:54:06.546: W/System.err(909):  at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:553)
06-20 02:54:06.546: W/System.err(909):  at dalvik.system.NativeStart.main(Native Method)