public function register_return_link($action, $params) {
        global $PAGE;
        $params['action'] = $action;
        $cm = $this->get_course_module();
        if ($cm) {
            $currenturl = new moodle_url('/mod/assign/view.php', array('id' => $cm->id));
        } else {
            $currenturl = new moodle_url('/mod/assign/index.php', array('id' => $this->get_course()->id));
        }

        $currenturl->params($params);
        $PAGE->set_url($currenturl);
    }