几个常用判断

        protected string AppPath(HttpRequest req)
        {
            string path = string.Empty;
            try
            {
                path = req.ApplicationPath != "/"
                    ? req.ApplicationPath + "/"
                    : req.ApplicationPath;

            }
            catch (Exception e)
            {
                throw e;
            }
            return path;
        }





        protected string UrlPrefix(HttpRequest req)
        {
            string path = "http://"
                            + req.Url.Host.ToString();

            path += req.ApplicationPath != "/"
                    ? req.ApplicationPath + "/"
                    : req.ApplicationPath;
            return path;
        }


/*
         * <%# Eval("数据字段") %>  中Eval方法有两次重载
         *     Eval(string expression)  返回为object
         *     Eval(string expression,string format) 返回为string
         */
        public string GetLen(string str, int length)
        {
            if (str != null && str != string.Empty)
                str = str.Length > length
                    ? str.Substring(0, length) : str;
            else
                str = string.Empty;
            return str;

        }