获得指定目录路径

1.自己实现的找到指定路径，感觉方法不太好，有其他方法的记得交流下，让我学习下哈

 class StringHelpUnity
    {
        /// <summary>
        /// 返回指定索引目录路径,(原目录索引为0)获取上一级目录则将index=-1，
        /// 上上一级目录index=-2，依次论推...
        /// </summary>
        /// <param name="old_Catalog">原目录路径</param>
        /// <param name="index">相对于旧目录(索引定义为0)的索引
        /// ，例如：获取上一级目录则将index=-1，上上一级目录index=-2，依次论推...
        /// </param>
        /// <returns></returns>
        public static string Catalog(string old_Catalog,int index)
        {
            string new_String = "";
            switch (index)
            {
                case -1:
                    new_String = old_Catalog.Substring(0, old_Catalog.LastIndexOf('\'));
                    break;
                case -2:
                    new_String= old_Catalog.Substring(0, old_Catalog.LastIndexOf('\'));
                    new_String = new_String.Substring(0, new_String.LastIndexOf('\'));
                    break;
                case -3:
                    new_String = old_Catalog.Substring(0, old_Catalog.LastIndexOf('\'));
                    new_String = new_String.Substring(0, new_String.LastIndexOf('\'));
                    new_String = new_String.Substring(0, new_String.LastIndexOf('\'));
                    break;
                default:
                    new_String = old_Catalog;
                    break;
            }
            return new_String;
        }
}