在获取当前纬度和经度时获取nul对象引用

Question

我正在为我的项目获取当前的纬度和经度，起初它运行得很好，但现在我正在检索空值。我确实打开了Location，并在物理设备中授予了该位置的权限，但仍然得到了null值。我的代码是

mMap.setMyLocationEnabled(true);
LocationManager locationManager = (LocationManager) getSystemService(Context.LOCATION_SERVICE);
Criteria criteria = new Criteria();
if (checkSelfPermission(Manifest.permission.ACCESS_FINE_LOCATION) != PackageManager.PERMISSION_GRANTED && checkSelfPermission(Manifest.permission.ACCESS_COARSE_LOCATION) != PackageManager.PERMISSION_GRANTED) {
// TODO: Consider calling
//    Activity#requestPermissions
// here to request the missing permissions, and then overriding
//   public void onRequestPermissionsResult(int requestCode, String[] permissions,
//                                          int[] grantResults)
// to handle the case where the user grants the permission. See the documentation
// for Activity#requestPermissions for more details.
return;
}
Location location = locationManager.getLastKnownLocation(locationManager.getBestProvider(criteria, false));
double cLatitude = location.getLatitude();
double cLongitude = location.getLongitude();
LatLng currentLocation = new LatLng(cLatitude, cLongitude);
System.out.println("Current Location : "+cLatitude+", "+cLongitude);
mMap.moveCamera(CameraUpdateFactory.newLatLngZoom(new LatLng(cLatitude, cLongitude), 13f));

我得到的错误是

java.lang.NullPointerException: Attempt to invoke virtual method 'double android.location.Location.getLatitude()' on a null object reference

Answer 1

添加LocationListener以获取当前位置。

private void getLocation() {
// Get the location manager
LocationManager locationManager = (LocationManager) 
getSystemService(LOCATION_SERVICE);
Criteria criteria = new Criteria();
String bestProvider = locationManager.getBestProvider(criteria, false);
Location location = locationManager.getLastKnownLocation(bestProvider);
LocationListener loc_listener = new LocationListener() {
public void onLocationChanged(Location l) {}
public void onProviderEnabled(String p) {}
public void onProviderDisabled(String p) {}
public void onStatusChanged(String p, int status, Bundle extras) {}
};
locationManager
.requestLocationUpdates(bestProvider, 0, 0, loc_listener);
location = locationManager.getLastKnownLocation(bestProvider);
try {
lat = location.getLatitude();
lon = location.getLongitude();
} catch (NullPointerException e) {
}
}

Answer 2

问题出在哪里？如果没有检索到任何位置，则可以使用空位置，例如，因为您在建筑物中。

这里有一种更稳健的方法来检索位置

LocationManager mLocationManager;
Location myLocation = getLastKnownLocation();
private Location getLastKnownLocation() {
mLocationManager = (LocationManager)getApplicationContext().getSystemService(LOCATION_SERVICE);
List<String> providers = mLocationManager.getProviders(true);
Location bestLocation = null;
for (String provider : providers) {
Location l = mLocationManager.getLastKnownLocation(provider);
if (l == null) {
continue;
}
if (bestLocation == null || l.getAccuracy() < bestLocation.getAccuracy()) {
// Found best last known location: %s", l);
bestLocation = l;
}
}
return bestLocation;
}

请注意，建议使用fused location provider:https://developer.android.com/training/location/retrieve-current