当我读取GPS定位时，Android返回null

<uses-permission android:name="android.permission.ACCESS_FINE_LOCATION" />
<uses-permission android:name="android.permission.ACCESS_COARSE_LOCATION" />

if (ContextCompat.checkSelfPermission(this, Manifest.permission.ACCESS_FINE_LOCATION) != PackageManager.PERMISSION_GRANTED) {
    ActivityCompat.requestPermissions(this, new String[]{Manifest.permission.ACCESS_FINE_LOCATION}, REQUEST_CODE);
}

LocationManager locationManager = (LocationManager) getSystemService(Context.LOCATION_SERVICE);
if (!locationManager.isProviderEnabled(LocationManager.GPS_PROVIDER)) {
    Intent intent = new Intent(Settings.ACTION_LOCATION_SOURCE_SETTINGS);
    startActivity(intent);
}

LocationManager locationManager = (LocationManager) getSystemService(Context.LOCATION_SERVICE);
if (!locationManager.isProviderEnabled(LocationManager.GPS_PROVIDER) && !locationManager.isProviderEnabled(LocationManager.NETWORK_PROVIDER)) {
    // 定位服务不可用
}

LocationManager locationManager = (LocationManager) getSystemService(Context.LOCATION_SERVICE);
locationManager.requestLocationUpdates(LocationManager.GPS_PROVIDER, 0, 0, new LocationListener() {
    @Override
    public void onLocationChanged(Location location) {
        // 定位数据已更新
    }

    @Override
    public void onStatusChanged(String provider, int status, Bundle extras) {
    }

    @Override
    public void onProviderEnabled(String provider) {
    }

    @Override
    public void onProviderDisabled(String provider) {
    }
});