GravityView Force not logged users to login before seeing the single entry view

gv-redirect-login-page.php

<?php
/*
Plugin Name: GravityView - force login before single view
Plugin URI: https://gravityview.co/
Description: Redirect visitors to login page before seeing the single entry view
Author: Katz Web Services, Inc.
Version: 1.0.0
Author URI: http://www.katzwebservices.com

Copyright 2015 Katz Web Services, Inc.  (email: info@katzwebservices.com)

This program is free software; you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation; either version 3 of the License, or
(at your option) any later version.

This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
GNU General Public License for more details.

You should have received a copy of the GNU General Public License
along with this program.  If not, see <http://www.gnu.org/licenses/>.

*/

// tested with GravityView version 1.5.3

/** 
 * Please adapt the login page to your own needs. Default is to WordPress login screen.
 * 
 * Thanks to http://kovshenin.com/2012/current-url-in-wordpress/
 */

add_action( 'template_redirect', 'my_gv_force_login');
function my_gv_force_login() {
	if( class_exists('GravityView_frontend') && GravityView_frontend::is_single_entry() ) {
		if( !is_user_logged_in() ) {
			global $wp;
			$current_url = add_query_arg( $wp->query_string, '', home_url( $wp->request ) );
			wp_redirect( wp_login_url( $current_url ), 301 );
			exit;
		}
	}
}