public function link_for_activitylink() {
        global $DB;
        $module = $DB->get_record('course_modules', array('id' => $this->properties->activitylink));
        if ($module) {
            $modname = $DB->get_field('modules', 'name', array('id' => $module->module));
            if ($modname) {
                $instancename = $DB->get_field($modname, 'name', array('id' => $module->instance));
                if ($instancename) {
                    return html_writer::link(new moodle_url('/mod/'.$modname.'/view.php',
                        array('id' => $this->properties->activitylink)), get_string('activitylinkname',
                        'lesson', $instancename), array('class' => 'centerpadded lessonbutton standardbutton p-r-1'));
                }
            }
        }
        return '';
    }