解决 locationManager.getLastKnownLocation 为null

private Location getLastKnownLocation() {
        if (ActivityCompat.checkSelfPermission(this, Manifest.permission.ACCESS_FINE_LOCATION) != PackageManager.PERMISSION_GRANTED && ActivityCompat.checkSelfPermission(this, Manifest.permission.ACCESS_COARSE_LOCATION) != PackageManager.PERMISSION_GRANTED) {
            return null;
        }
        LocationManager locationManager = (LocationManager) getSystemService(LOCATION_SERVICE);
        List providers = locationManager.getAllProviders();
        Location bestLocation = null;
        for (String provider : providers) {

            Location l = locationManager.getLastKnownLocation(provider);
            if (l == null) {
                continue;
            }
            if (bestLocation == null || l.getAccuracy() < bestLocation.getAccuracy()) {
                // Found best last known location: %s", l);
                bestLocation = l;
            }
        }
        return bestLocation;
    }