EventNotificationContent 消息怎么创建

case eventNotification:
        //处理事件提醒消息
        EventNotificationContent eventNotificationContent = (EventNotificationContent)msg.getContent();
        switch (eventNotificationContent.getEventNotificationType()){
            case group_member_added:
            //群成员加群事件
            break;
            case group_member_removed:
            //群成员被踢事件
            break;
            case group_member_exit:
            //群成员退群事件
            break;
        }
        break;