NullpointerException when calling getSystemService(Context.LOCATION_SERVICE) and onLocationChanged not called

问题:

I am trying to create a background service that updates the current gps position. I am getting a NullPointerException at line LocationManager lm = (LocationManager) getSystemService(Context.LOCATION_SERVICE);

HomeActivity launches a service

startService(new Intent(getApplicationContext(), ForHire.class)); 

Service (ForHire) creates a TimerTask Updates

public class ForHire extends Service {  ... private Timer getUpdatesNow = new Timer(); private Updates updates = new Updates(getUpdatesNow);  @Override public void onCreate() {     ...     getUpdatesNow.schedule(updates, God.KM20TIME);     Log.v("Taxeeta", "Notification created"); }      private class Updates extends TimerTask implements LocationListener {     private Timer getUpdatesNow;      public Updates(Timer newGetUpdatesNow) {         super();         getUpdatesNow = newGetUpdatesNow;         LocationManager lm = (LocationManager) getSystemService(Context.LOCATION_SERVICE);         lm.requestLocationUpdates(LocationManager.GPS_PROVIDER,                 God.KM20TIME, God.KM20DISTANCE, (LocationListener) this);     }     public void run() {         ...         //do some cleanup     }             @Override     public void onLocationChanged(Location location) {         Log.v("Taxeeta", "Location changed");         // do a update of the current location.     } 

The first issue is that I get that NullPointerException. Second issue is that onLocationChanged is never called if I comment out LocationManager lm = (LocationManager) getSystemService(Context.LOCATION_SERVICE); lm.requestLocationUpdates(LocationManager.GPS_PROVIDER, God.KM20TIME, God.KM20DISTANCE, (LocationListener) this); these 2 lines.

My Manifest

<uses-permission android:name="android.permission.ACCESS_FINE_LOCATION" /> <uses-permission android:name="android.permission.ACCESS_COARSE_LOCATION" /> <uses-permission android:name="android.permission.INTERNET" /> <uses-permission android:name="android.permission.READ_PHONE_STATE" /> <uses-permission android:name="android.permission.ACCESS_WIFI_STATE" /> <uses-permission android:name="android.permission.CALL_PHONE" /> <application ...>    ...    <uses-library android:name="com.google.android.maps" /> </application> 

What am I missing here ?

Edit : Values of KM20TIME = 5000 (5seconds), and KM20DISTANCE = 1 (1meter). Apart from the fix's below, I walked out of my house, got GPS enabled and walked from one corner of my balcony to the other. I noticed that my gps (LSB) changed as I walked from one corner to the other every 5 seconds.

回答1:

The earliest you can call new Updates(getUpdatesNow); is inside your Service's onCreate() method. The simple reason is that getSystemService() requires a valid Context which doesn't exist before entering onCreate().

Try:

private Timer getUpdatesNow; private Updates updates;  @Override public void onCreate() {     ...     getUpdatesNow = new Timer();     updates = new Updates(getUpdatesNow); 

回答2:

// Acquire a reference to the system Location Manager LocationManager locationManager = (LocationManager) getSystemService(Context.LOCATION_SERVICE);  // Define a listener that responds to location updates Location location = locationManager.getLastKnownLocation(LocationManager.NETWORK_PROVIDER);  if (location != null) {     Toast.makeText(getBaseContext(),                             "Last Location is found..",                             Toast.LENGTH_LONG).show();   } else {      Toast.makeText(getBaseContext(),                             "Last Location is not found..",                             Toast.LENGTH_LONG).show(); } LocationListener locationListener = new LocationListener() { public void onStatusChanged(String provider,     int status, Bundle extras) { } public void onProviderEnabled(String provider) {     Toast.makeText(getApplicationContext(),         "Gps Enabled", Toast.LENGTH_SHORT).show(); } public void onProviderDisabled(String provider) {     Toast.makeText(getApplicationContext(),         "Gps Disabled", Toast.LENGTH_SHORT).show(); }  @Override public void onLocationChanged(Location location) {     Log.i("geolocation",         "lat is : " + location.getLatitude()         + " and " + location.getLongitude()         + "");     Toast.makeText(getBaseContext(),     "Location is Changed..", Toast.LENGTH_LONG)         .show(); } }; // Register the listener with the Location Manager to receive location updates locationManager.requestLocationUpdates( LocationManager.GPS_PROVIDER, 0, 0, locationListener); 

回答3:

@Override public void onCreate() {      new Updates(getUpdatesNow);     ...     getUpdatesNow.schedule(updates, God.KM20TIME);     Log.v("Taxeeta", "Notification created"); } 

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