android中的位置为null

Question

I'm trying to get my location. But zero is all that I've got. Please look at the code:

 public class ListBranchesActivity extends Activity {       

    private double lat, lon;

    private LocationManager lm;
    private Location location;

    private final LocationListener locationListener = new LocationListener() {
        public void onLocationChanged(Location location) {
            lon = location.getLongitude();
            lat = location.getLatitude();
        }

        @Override
        public void onStatusChanged(String provider, int status, Bundle extras) {
            // TODO Auto-generated method stub

        }

        @Override
        public void onProviderEnabled(String provider) {
            // TODO Auto-generated method stub

        }

        @Override
        public void onProviderDisabled(String provider) {
            // TODO Auto-generated method stub

        }
    };

And then somewhere in onCreate() :

lm = (LocationManager) getSystemService(Context.LOCATION_SERVICE);
        lm.requestLocationUpdates(LocationManager.GPS_PROVIDER, 2000, 10,
                locationListener);
        location = lm.getLastKnownLocation(LocationManager.GPS_PROVIDER);

The following code returns NullPointerException:

   Log.w("es09", "coordinates are " + lon + " " + lat +" " +location.getLatitude()+" "+ location.getLongitude());

And that code returns "coordinates are 0.0 0.0"

 Log.w("es09", "coordinates are " + lon + " " + lat);

My manifest permissions:

<uses-permission android:name="android.permission.ACCESS_NETWORK_STATE" />
   <uses-permission android:name="android.permission.READ_EXTERNAL_STORAGE" />
   <uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE" />
   <uses-permission android:name="android.permission.READ_INTERNAL_STORAGE" />
   <uses-permission android:name="android.permission.WRITE_INTERNAL_STORAGE" />
   <uses-permission android:name="android.permission.ACCESS_COARSE_LOCATION" />
   <uses-permission android:name="android.permission.ACCESS_FINE_LOCATION" />
   <uses-permission android:name="android.permission.ACCESS_WIFI_STATE" />
   <uses-permission android:name="android.permission.INTERNET" />
   <uses-permission android:name="android.permission.CALL_PHONE" />
   <uses-permission android:name="android.permission.READ_PHONE_STATE"/>
   <uses-permission android:name="android.permission.ACCESS_COARSE_LOCATION"/>
   <uses-permission android:name="android.permission.ACCESS_GPS"/>
   <uses-permission android:name="android.permission.ACCESS_LOCATION"/>
   <uses-permission android:name="android.permission.ACCESS_ASSISTED_GPS"/>

What is wrong?

Answer 1

The problem is that you are assuming that you always get a location back and that is NOT the case. There is no guarentee that a location is returned to you so you have to check for null.

using

lm.getLastKnownLocation(LocationManager.GPS_PROVIDER);

is no guarantee that a last location exists, anytime you get a location you ALWAYS should check to make sure it is not null FIRST!

Answer 2

Use NETWORK_PROVIDER to get location because many times GPS will give null latitude and longitude

m_locationManager.requestLocationUpdates(LocationManager.NETWORK_PROVIDER,0,0, this);
    m_location = m_locationManager.getLastKnownLocation(LocationManager.NETWORK_PROVIDER);

Add below permissions in manifest

<uses-permission android:name="android.permission.INTERNET" />
<uses-permission android:name="android.permission.ACCESS_FINE_LOCATION" />
<uses-permission android:name="android.permission.ACCESS_COARSE_LOCATION" />
<uses-permission android:name="android.permission.ACCESS_NETWORK_STATE" />
<uses-permission android:name="android.permission.CHANGE_NETWORK_STATE" />
<uses-permission android:name="android.permission.ACCESS_WIFI_STATE" />
<uses-permission android:name="android.permission.CHANGE_WIFI_STATE" />