@Override
    public void onRequestPermissionsResult(int requestCode, @NonNull String[] permissions, @NonNull int[] grantResults) {
        switch (requestCode) {
            case MY_PERMISSIONS_REQUEST_FILE_ACCESS:
                // if permission has not been granted
                if (grantResults.length > 0
                        && grantResults[0] == PackageManager.PERMISSION_GRANTED) {
                    grantLocationPerms();
                } else {
                    // ask the user to grant permissions manually
                    manualPermissionDialog();
                }
                break;
            ...
}