Support

December 14, 2016 at 8:29 am

I gather that you’re not going to update to the current version then?

So what you would need to do is add a shim to your site:

if( ! function_exists('get_preview_post_link') ) {
function get_preview_post_link( $post = null, $query_args = array(), $preview_link = '' ) {
    $post = get_post( $post );
    if ( ! $post ) {
        return;
    }
 
    $post_type_object = get_post_type_object( $post->post_type );
    if ( is_post_type_viewable( $post_type_object ) ) {
        if ( ! $preview_link ) {
            $preview_link = set_url_scheme( get_permalink( $post ) );
        }
 
        $query_args['preview'] = 'true';
        $preview_link = add_query_arg( $query_args, $preview_link );
    }
 
    /**
     * Filters the URL used for a post preview.
     *
     * @since 2.0.5
     * @since 4.0.0 Added the <code>$post</code> parameter.
     *
     * @param string  $preview_link URL used for the post preview.
     * @param WP_Post $post         Post object.
     */
    return apply_filters( 'preview_post_link', $preview_link, $post );
}
}

You can add the above to a functions plugin or into your WordPress theme’s functions.php file. Then later on, if you ever end up maintaining your site and updating to a current version of WordPress, you can remove the shim.