asp.net 生成验证码问题 1.添加一个.ashx文件<%@ WebHandler Language="C#" class="CheckCode" %>using System;using System.Web;using System.Drawing;public class CheckCode : IHttpHandler {    public void ProcessRequest(HttpContext context)    {        string g = GenerateCheckCode();        CreateCheckCodeImage(g);    }    public bool IsReusable    {        get        {            return false;        }    }    private string GenerateCheckCode()    {        int number;        char code;        string checkCode = String.Empty;        System.Random random = new Random();         for (int i = 0; i < 5; i++)        {            number = random.Next();            if (number % 2 == 0)                //生成‘0‘-‘9‘字符                code = (char)(‘0‘ + (char)(number % 10));            else                //生成‘A‘-‘Z‘字符                code = (char)(‘A‘ + (char)(number % 26));            checkCode += code.ToString();        }        HttpContext.Current.Response.Cookies.Add(new HttpCookie("checkcode", checkCode));        return checkCode;        //两个字符相加等于=asicc码加    }    private void CreateCheckCodeImage(string checkCode)    {        if (checkCode == null || checkCode.Trim() == String.Empty)            return;        //(int)Math.Ceiling((checkCode.Length * 12.5)),22        System.Drawing.Bitmap image = new System.Drawing.Bitmap(80, 30);        Graphics g = Graphics.FromImage(image);        try        {            //生成随机生成器            Random random = new Random();            //清空图片背景色            g.Clear(Color.White);            //画图片的背景噪音线            for (int i = 0; i < 5; i++)            {                int x1 = random.Next(image.Width+10);                int x2 = random.Next(image.Width+10);                int y1 = random.Next(image.Height+10);                int y2 = random.Next(image.Height+10);                Pen p = new Pen(Color.Gray, 4);                g.DrawLine(p, x1, y1, x2, y2);            }            Font font = new System.Drawing.Font("Arial", 15, (System.Drawing.FontStyle.Bold | System.Drawing.FontStyle.Italic));            System.Drawing.Drawing2D.LinearGradientBrush brush = new System.Drawing.Drawing2D.LinearGradientBrush(new Rectangle(0, 0, image.Width, image.Height), Color.Blue, System.Drawing.Color.DarkRed, 1.2f, true);            g.DrawString(checkCode, font, brush, 5, 5);            //画图片的前景噪音点            for (int i = 0; i < 200; i++)            {                int x = random.Next(image.Width);                int y = random.Next(image.Height);                image.SetPixel(x, y, System.Drawing.Color.FromArgb(random.Next()));            }            //画图片的边框线            g.DrawRectangle(new System.Drawing.Pen(System.Drawing.Color.Silver), 0, 0, image.Width - 1, image.Height - 1);            System.IO.MemoryStream ms = new System.IO.MemoryStream();            image.Save(ms, System.Drawing.Imaging.ImageFormat.Gif);            HttpContext.Current.Response.ClearContent();            HttpContext.Current.Response.ContentType = "image/jpg";            HttpContext.Current.Response.BinaryWrite(ms.ToArray());        }        finally        {            g.Dispose();            image.Dispose();        }    }    }2.在用到验证码的界面添加一个img控件，并且src属性指向.ashx文件<img alt="看不清，换一张" src=http://www.mamicode.com/"CheckCode.ashx" onclick="this.src=http://www.mamicode.com/‘CheckCode.ashx?abc=‘+Math.random()" />3.提交后先判断验证码是否正确 //检查验证码是否正确        if(this.txt_checkcode.Text.ToLower ()!=this.Request.Cookies["checkcode"].Value.ToLower () )        {            //写脚本提示           if( this.ClientScript.IsStartupScriptRegistered ("checkcode")==false)           {               this.ClientScript.RegisterStartupScript(this.GetType (),"checkcode","<script>alert(‘验证码错误!‘);</script>");           }            return;        }