利用ashx生成验证码，并解决只能点击一次刷新问题

验证码是大家常用的功能，主要是防止非法用户或不怀好意的暴力登录系统。现在就介绍利用ashx一般处理程序来生成随机验证码。

1.新建ashx文件，并继承接口：IHttpHandler,IRequiresSessionState。

   1）生成数字和字母的随机字符串

     /// <summary>
    /// 生成验证码字符串（字母和数字组合，也可以拓展到汉字）
    /// </summary>
    /// <param name="codeLen">验证码字符长度</param>
    /// <returns>返回验证码字符串</returns>
    private string MakeCode(int codeLen)
    {
        if (codeLen < 1)
        {
            return string.Empty;
        }

        int number;
        string checkCode = string.Empty;
        Random random = new Random();

        for (int index = 0; index < codeLen; index++)
        {
            number = random.Next();

            if (number % 2 == 0)
            {
                checkCode += (char)('0' + (char)(number % 10));     //生成数字
            }
            else
            {
                checkCode += (char)('A' + (char)(number % 26));     //生成字母
            }
        }

        return checkCode;
    }

   2）生成带字符串的验证码图片流

///<summary>
    /// 获取验证码图片流
    /// </summary>
    /// <param name="checkCode">验证码字符串</param>
    /// <returns>返回验证码图片流</returns>
    private MemoryStream CreateCodeImg(string checkCode)
    {
        if (string.IsNullOrEmpty(checkCode))
        {
            return null;
        }

        Bitmap image = new Bitmap((int)Math.Ceiling((checkCode.Length * 12.5)), 22);

        Graphics graphic = Graphics.FromImage(image);

        try
        {
            Random random = new Random();

            graphic.Clear(Color.White);

            int x1 = 0, y1 = 0, x2 = 0, y2 = 0;

            for (int index = 0; index < 25; index++)
            {
                x1 = random.Next(image.Width);
                x2 = random.Next(image.Width);
                y1 = random.Next(image.Height);
                y2 = random.Next(image.Height);

                graphic.DrawLine(new Pen(Color.Silver), x1, y1, x2, y2);
            }

            Font font = new Font("Arial", 12, (FontStyle.Bold | FontStyle.Italic));
            LinearGradientBrush brush = new LinearGradientBrush(new Rectangle(0, 0, image.Width, image.Height), Color.Red, Color.DarkRed, 1.2f, true);
            graphic.DrawString(checkCode, font, brush, 2, 2);

            int x = 0;
            int y = 0;

            //画图片的前景噪音点
            for (int i = 0; i < 100; i++)
            {
                x = random.Next(image.Width);
                y = random.Next(image.Height);

                image.SetPixel(x, y, Color.FromArgb(random.Next()));
            }

            //画图片的边框线
            graphic.DrawRectangle(new Pen(Color.Silver), 0, 0, image.Width - 1, image.Height - 1);

            //将图片验证码保存为流Stream返回
            System.IO.MemoryStream ms = new System.IO.MemoryStream();
            image.Save(ms, System.Drawing.Imaging.ImageFormat.Gif);
            return ms;
        }
        finally
        {
            graphic.Dispose();
            image.Dispose();
        }

  3）在public void ProcessRequest (HttpContext context1) 中调用

 string chkCode = string.Empty;
    HttpContext context;
    public void ProcessRequest (HttpContext context1) {
        this.context = context1;
        //生成四位的随机码
        string chkCode = MakeCode(4);
        //保存Session中，以便方便验证
        context.Session["chkCode"] = chkCode;
        //无需缓存
        context.Response.Cache.SetCacheability(HttpCacheability.NoCache);
        context.Response.ClearContent();
        //设置图片类型
        context.Response.ContentType = "image/Png";
        MemoryStream ms = CreateCodeImg(chkCode);
        if (null != ms)
        {
            context.Response.BinaryWrite(ms.ToArray());
        }
    }

2.web页面调用ashx文件，生成验证码：

，在web文件中定义一个img控件，然后在scr属性中指向ashx文件。

   <img id="img" title="点击这里换一个" src="../Action/tools/VerificationCode.ashx" />，利用jquery，给img添加点击事件，实现点击刷新验证码。

$("#img").click(function () {
                $("img").attr("src","").attr("src", "../action/tools/VerificationCode.ashx");
            })

启动页面就可以看到验证码，但按照上面的方法添加点击事件时只可以点击一次进行刷新，以后再点击验证码不变。

3.解决验证码只能点击一次的问题

将上面的点击事件方法变更为： $("img").attr("src","").attr("src", "../action/tools/VerificationCode.ashx?xx="+new Date());即可实现每次点击都刷新验证码。