Revslider metabox in page

revslider-metabox-for-page.php

<?php

/**
* Plugin Name: Revslider metabox for page
* Plugin URI: https://premium.wpmudev.org/
* Description: Revslider metabox for page
* Author: Ariful Islam @ WPMUDEV
* Author URI: https://premium.wpmudev.org/profile/itsarifulislam
* License: GPLv2 or later
*/


if ( ! defined( 'ABSPATH' ) ) {
	exit;
}


if ( ! class_exists( 'RevSliderMetaboxForPage' ) ) {

	class RevSliderMetaboxForPage {

		private static $_instance 	= null;
		
		public static function get_instance() {

			if ( is_null( self::$_instance ) ) {
				self::$_instance = new RevSliderMetaboxForPage();
			}

			return self::$_instance;

		}

		private function __construct() {

			if ( !class_exists('RevSlider') ) return;

			add_action( 'add_meta_boxes', array( $this, 'add_meta_boxes' ), 10 );

			add_action( 'save_post', array( $this, 'save_meta_boxes' ), 10, 1 );
			
		}

		public function add_meta_boxes() {

			add_meta_box( 'featured_rev_slider', __( 'Featured Revolution Slider', 'textdomain' ), array( $this, 'render_featured_revslider_metabox_content' ), 'page', 'side' );

		}

		public function save_meta_boxes( $post_id ) {

			if (
				! isset( $_POST['featured_rev_slider'] ) || 
				! isset( $_POST['featured_revslider_meta_box_nonce'] ) || 
				! wp_verify_nonce( $_POST['featured_revslider_meta_box_nonce'], 'featured_revslider_meta_box' ) || 
				! current_user_can( 'edit_post', $post_id )
			) 
			return;
     
			update_post_meta( $post_id, 'featured_rev_slider', sanitize_text_field($_POST['featured_rev_slider']) );

		}

		public function render_featured_revslider_metabox_content() {

			global $post;

			$slider = new RevSlider();
			$revolution_sliders = $slider->getArrSliders();
			$meta = get_post_meta($post->ID, 'featured_rev_slider', true);

			wp_nonce_field( 'featured_revslider_meta_box', 'featured_revslider_meta_box_nonce' );

			echo '<select name="featured_rev_slider" id="featured_rev_slider">';

				echo "<option value=''>--- Revolution Sliders ---</option>";
				
				foreach ( $revolution_sliders as $revolution_slider ) {
					$checked="";
					$alias = $revolution_slider->getAlias();
					$title = $revolution_slider->getTitle();
					if ( $alias==$meta ) $checked = "selected";
					echo "<option value='".$alias."' $checked>".$title."</option>";
				}

			echo '</select>';

		}

	}

	function Render_revslider_metabox_for_page(){

		$GLOBALS['RevSliderMetaboxForPage'] = RevSliderMetaboxForPage::get_instance();

	}

}

add_action( 'init', 'Render_revslider_metabox_for_page' );