asp.net扩展Login控件，添加图文验证码

对asp.net提供的Login控件进行扩展，在密码后面加一图文验证功能以防止自动注册程序。
1.添加imageValidate.aspx，在头部添加信息
<% Response.Buffer = true ;%>
<% Response.ExpiresAbsolute = DateTime.Now.AddSeconds(-1);%>
<% Response.Expires = 0 ;%>
<% Response.CacheControl = "no-cache" ; %>
在imageValidate.aspx.cs中的代码如下：
protected void Page_Load(object sender, EventArgs e)
    {
        //生成4位的验证码
        /*string tmp = RndNum(4);
        HttpCookie cookie = new HttpCookie("ImageV", tmp);
        //Response.Cookies["ImageV"].Value=tmp;
        Response.Cookies.Add(cookie);
        this.ValidateCode(tmp);*/

        CreateCheckCodeImage(GenerateCheckCode());

    }

    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)
                code = (char)('0' + (char)(number % 10));
            else
                code = (char)('A' + (char)(number % 26));

            checkCode += code.ToString();
        }
        Session["CheckCode"] = checkCode;
      
       
        //Response.Cookies.Add(new HttpCookie("CheckCode", checkCode));

        return checkCode;
    }

    private void CreateCheckCodeImage(string checkCode)
    {
        if (checkCode == null || checkCode.Trim() == String.Empty)
            return;

        System.Drawing.Bitmap image = new System.Drawing.Bitmap((int)Math.Ceiling((checkCode.Length * 12.5)), 22);
        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 < 25; i++)
            {
                int x1 = random.Next(image.Width);
                int x2 = random.Next(image.Width);
                int y1 = random.Next(image.Height);
                int y2 = random.Next(image.Height);

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

            Font font = new System.Drawing.Font("Arial", 12, (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, Color.DarkRed, 1.2f, true);
            g.DrawString(checkCode, font, brush, 2, 2);

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

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

            //画图片的边框线
            g.DrawRectangle(new Pen(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);
            Response.ClearContent();
            Response.ContentType = "image/Gif";
            Response.BinaryWrite(ms.ToArray());
        }
        finally
        {
            g.Dispose();
            image.Dispose();
        }
    }
这就是生成验证码的页面
2.将这页面添加到login控件中：
拖曳一Login控件，将之切换到模式下，在Html源文件中在表格中密码那行后添加：
 
   
        验证码:
   
 
 
  
    
    
  
 

其中ImageUrl="~/public/imageValidate.aspx“ 的imageValidate.aspx指的就是我们第一步建立的文件。
3.在login控件的authenticate事件中加入代码
protected void Login1_Authenticate(object sender, AuthenticateEventArgs e)
    {
        TextBox txtImage = Login1.FindControl("txtImgValid") as TextBox;
       
      
        if (Session["CheckCode"] == null)
        {
            Response.Write("");
            e.Authenticated = false;
            return;
        }
       
        if (String.Compare(Session["CheckCode"] .ToString(),txtImage.Text,true)!=0)
        {
            Response.Write("");
            e.Authenticated = false;
            return;
        }
     
        e.Authenticated = true;
       

    }

单击登录按钮后顺便将session清空
protected void LoginButton_Click(object sender, EventArgs e)
    {
        Session["CheckCode"] = null;
    }
运行结果如图：