How to find out why GPS coordinates are missing in

问题:

I am trying to get a device's location information using GPS, but for some reason one of the two coordinates is missing sometimes.

This is the code:

LocationManager lm = (LocationManager) getSystemService(Context.LOCATION_SERVICE);
Location location = lm.getLastKnownLocation(LocationManager.GPS_PROVIDER);
double longitude = location.getLongitude();
double latitude = location.getLatitude();
Log.d("LOCATION1", "Longitude: " + longitude);
Log.d("LOCATION2", "Latitude: " + latitude);

Sometimes I do get both coordinates, but not always, which makes me think about some kind of delay somewhere. Is there a way to find out why a GPS coordinate is missing when this happens?

回答1:

Because the GPS isn't always on. getLastKnownLocation will return a location if it knows one and if it isn't too stale. Since nothing else was using the GPS, it doesn't know one. If you need a location, either requestLocationUpdates or requestSingleUpdate, which will turn on the GPS and get a new location.

回答2:

 Criteria criteria = new Criteria();
    LocationManager locationManager = (LocationManager) getSystemService(LOCATION_SERVICE);
   // mMap.addMarker(new MarkerOptions().position(sydney2).title("fi"));
    if (ActivityCompat.checkSelfPermission(this, Manifest.permission.ACCESS_FINE_LOCATION) != PackageManager.PERMISSION_GRANTED && ActivityCompat.checkSelfPermission(this, Manifest.permission.ACCESS_COARSE_LOCATION) != PackageManager.PERMISSION_GRANTED) {
        // TODO: Consider calling
        //    ActivityCompat#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 ActivityCompat#requestPermissions for more details.
        return;
    }
    locationManager.requestLocationUpdates(locationManager.getBestProvider(criteria, true), 2000, 0, new android.location.LocationListener() {
        @Override
        public void onLocationChanged(Location location) {
           // 
        }

in onLocationChanged method you can use location.getLatitude & location.getLongitude