/**
  * set class instance
  * @param $inst: an object instanceof this class
  */
 public static function setInstance($inst)
 {
     if ($inst instanceof HW_Conditions_Metabox) {
         self::$instance = $inst;
     }
 }
 /**
  * init metaboxs
  */
 public static function init_metabox()
 {
     if (is_admin()) {
         global $current_user;
         if (class_exists('HW_Conditions_Manager') && class_exists('HW_Conditions_Metabox') && current_user_can('administrator')) {
             new HW_Conditions_Manager(HW_Conditions_Manager::post_type);
             // the post type slug
             HW_Conditions_Metabox::setInstance(new HW_Conditions_Metabox(null, __('Thêm điều kiện'), array(HW_Conditions_Manager::post_type), 'normal', 'low'));
             //add new metabox
             new HW_Conditions_Metabox(null, __('Hướng dẫn'), array(HW_Conditions_Manager::post_type), 'normal', 'low');
         }
     }
 }