protected function view_grant_extension($mform) {
        global $CFG;
        require_once($CFG->dirroot . '/mod/assign/extensionform.php');

        $o = '';

        $data = new stdClass();
        $data->id = $this->get_course_module()->id;

        $formparams = array(
            'instance' => $this->get_instance(),
            'assign' => $this
        );

        $users = optional_param('userid', 0, PARAM_INT);
        if (!$users) {
            $users = required_param('selectedusers', PARAM_SEQUENCE);
        }
        $userlist = explode(',', $users);

        $keys = array('duedate', 'cutoffdate', 'allowsubmissionsfromdate');
        $maxoverride = array('allowsubmissionsfromdate' => 0, 'duedate' => 0, 'cutoffdate' => 0);
        foreach ($userlist as $userid) {
            // To validate extension date with users overrides.
            $override = $this->override_exists($userid);
            foreach ($keys as $key) {
                if ($override->{$key}) {
                    if ($maxoverride[$key] < $override->{$key}) {
                        $maxoverride[$key] = $override->{$key};
                    }
                } else if ($maxoverride[$key] < $this->get_instance()->{$key}) {
                    $maxoverride[$key] = $this->get_instance()->{$key};
                }
            }
        }
        foreach ($keys as $key) {
            if ($maxoverride[$key]) {
                $this->get_instance()->{$key} = $maxoverride[$key];
            }
        }

        $formparams['userlist'] = $userlist;

        $data->selectedusers = $users;
        $data->userid = 0;

        if (empty($mform)) {
            $mform = new mod_assign_extension_form(null, $formparams);
        }
        $mform->set_data($data);
        $header = new assign_header($this->get_instance(),
                                    $this->get_context(),
                                    $this->show_intro(),
                                    $this->get_course_module()->id,
                                    get_string('grantextension', 'assign'));
        $o .= $this->get_renderer()->render($header);
        $o .= $this->get_renderer()->render(new assign_form('extensionform', $mform));
        $o .= $this->view_footer();
        return $o;
    }