排序管理器

一个管理排序的类，支持多排序。
    环境:.NET,C#
    /// <summary>
    /// 排序管理器
    /// </summary>
    public class DBOrderByOpt
    {
        protected struct ____Task____
        {
            public string fieldName;
            public bool ASC;
            public ____Task____(string fieldName, bool ASC)
            {
                this.fieldName = fieldName;
                this.ASC = ASC;
            }
        };
        private IList<____Task____> orderByData;
        /// <summary>
        /// 默认构造函数
        /// </summary>
        public DBOrderByOpt()
        {
            orderByData = new List<____Task____>();
        }
        /// <summary>
        /// 增加排序字段并调整字段优先级
        /// </summary>
        public void AddChg(string fieldName)
        {
            bool asc = true;
            foreach (____Task____ data in orderByData)
            {
                if (data.fieldName.Trim() == fieldName.Trim())
                {
                    asc = !data.ASC;
                    orderByData.Remove(data);
                    break;
                }
            }
            orderByData.Add(new ____Task____(fieldName.Trim(), asc));
        }
        /// <summary>
        /// 增加排序字段但保持字段优先级
        /// </summary>
        public void AddUnChg(string fieldName)
        {
            int i = 0;
            bool asc = true;
            for (; i < orderByData.Count; i++)
            {
                if (orderByData.fieldName.Trim() == fieldName.Trim())
                {
                    asc = !orderByData.ASC;
                    orderByData.Remove(orderByData);
                    break;
                }
            }
            orderByData.Insert(i, new ____Task____(fieldName.Trim(), asc));
        }
        /// <summary>
        /// 获取正向排序字符串
        /// </summary>
        public string ToOrderString()
        {
            string orderStr = "";
            for (int i = 0; i < orderByData.Count; i++)
            {
                if (orderByData.ASC)
                    orderStr += orderByData.fieldName + " asc, ";
                else
                    orderStr += orderByData.fieldName + " desc, ";
            }
            if (orderStr.Trim() == "")
                return "";
            else
                return orderStr.Substring(0, orderStr.Length - 2);
        }
        /// <summary>
        /// 获取反向排序字符串
        /// </summary>
        public string ToReOrderString()
        {
            string orderStr = "";
            for (int i = orderByData.Count - 1; i >= 0; i--)
            {
                if (orderByData.ASC)
                    orderStr += orderByData.fieldName + " asc, ";
                else
                    orderStr += orderByData.fieldName + " desc, ";
            }
            if (orderStr.Trim() == "")
                return "";
            else
                return orderStr.Substring(0, orderStr.Length - 2);
        }
    }