一年后，一些人的技能有了很大的提高，你看：

Keep_Deleted_Attachment_File::on_load();

/**
 * Keep original file when deleting attachments.
 */
class Keep_Deleted_Attachment_File {

    static private $file;

    static function on_load() {

        add_action( \'init\', array( __CLASS__, \'init\' ) );
    }

    static function init() {

        add_action( \'delete_attachment\', array( __CLASS__, \'delete_attachment\' ) );
    }

    /**
     * @param int $post_id attachment being deleted
     */
    static function delete_attachment( $post_id ) {

        self::$file = get_attached_file( $post_id );
        add_filter( \'wp_delete_file\', array( __CLASS__, \'wp_delete_file\' ) );
    }

    /**
     * @param string $file path to file being deleted
     *
     * @return string|bool no change or boolean false to prevent file deletion
     */
    static function wp_delete_file( $file ) {

        if ( ! empty( self::$file ) && self::$file == $file ) {

            remove_filter( current_filter(), array( __CLASS__, __FUNCTION__ ) );
            return false;
        }

        return $file;
    }
}