php - Wordpress: how to start an add_filter inside Class -

sorry no-clear title.

i'm developing plugin , want add custom posts other columns (trying follow tutorial: https://ryanbenhase.com/how-to-add-custom-columns-to-the-all-posts-screen-or-your-custom-post-type-in-wordpress/ ).

in admin class have in __construct()

public function __construct() {      $this->perform_filter_hooked_action(); }   /**      * perform hooks filters      *       * @since 1.4       */     private function perform_filter_hooked_action() {          echo 'perform_filter_hooked_action called';         add_filter('manage_custom_posts_columns' , array ( $this , 'add_columns_to_summary_custom_post'));      }      /**      *       * filter add columns summary custom post.      *       * callback perform_filter_hooked_action      *       * @since 1.4      */     public function add_columns_to_summary_custom_post( $columns ) {          echo 'add_columns_to_summary_custom_post called';      } 

i on screen first echo (perform_filter_hooked_action called) not second 1 (that other on "add_columns_to_summary_custom_post called").

where wrong?

thank much

when use filters, need return value not echo it. maybe causing issue.

from documentation add_filter() function:

when filter later applied, each bound callback run in order of priority, , given opportunity modify value returning new value.