<?php
add_filter('rwmb_meta_boxes', function ($meta_boxes) {

	$meta_boxes[] = array(
			'id' => 'gallery',
			'title' => 'Galer&iacute;a',
			'pages' => array('page'),
			'context' => 'normal',
			'priority' => 'high',
			'fields' => array(
					array(
							'id' => 'post_gallery',
							'type' => 'file_advanced',
//							'max_file_uploads' => 1,
					),
			)
	);
	return $meta_boxes;
});

/**
 *
 * @param int $post_id
 * @return string|bool
 */
function get_gallery_shortcode($post_id = 0) {
	$gallery_ids = get_gallery_ids($post_id = 0);
	return !empty($gallery_ids) ? sprintf('[gallery ids="%s"]', implode(',', $gallery_ids)) : FALSE;
}

/**
 *
 * @param type $post_id
 * @return type
 */
function get_gallery_ids($post_id = 0) {
	$post_id = (is_numeric($post_id) && 0 < $post_id) ? (int) $post_id : get_the_ID();
	return get_post_meta(get_the_ID(),'post_gallery');
}