验证码

验证码类：
using System.Drawing;
public partial class validateNum : System.Web.UI.Page
    {
        protected void Page_Load(object sender, EventArgs e)
        {
            if (!IsPostBack)
            {
                string validateNum = CreateRandomNum(4);//成生位随机字符串
                CreateImage(validateNum);//将生成的随机字符串绘成图片
                Session["ValidateNum"] = validateNum;//保存验证码
            }
        }
        //生成随机字符串
        private string CreateRandomNum(int NumCount)
        {
            string allChar = "0,1,2,3,4,5,6,7,8,9,A,B,C,D,E,F,G,H,I,J,K,L,M,N,O,P,Q,R,S,T,U,W,X,Y,Z";
            string[] allCharArray = allChar.Split(',');//拆分成数组
            string randomNum = "";
            int temp = -1;//记录上次随机数的数值，尽量避免产生几个相同的随机数

            Random rand = new Random();
            for (int i = 0; i < NumCount; i++)
            {
                if (temp != -1)
                {
                    rand = new Random(i * temp * ((int)DateTime.Now.Ticks));
                }
                int t = rand.Next(35);
                if (temp == t)
                {
                    return CreateRandomNum(NumCount);
                }
                temp = t;
                randomNum += allCharArray[t];
            }
            return randomNum;
        }




        //生成图片
        private void CreateImage(string validateNum)
        {
            if (validateNum == null || validateNum.Trim() == String.Empty)
                return;
            //生成Bitmap图像
            System.Drawing.Bitmap image = new System.Drawing.Bitmap(validateNum.Length * 12 + 10, 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(validateNum, 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();
                //将图像保存到指定的流
                image.Save(ms, System.Drawing.Imaging.ImageFormat.Gif);
                Response.ClearContent();
                Response.ContentType = "image/Gif";
                Response.BinaryWrite(ms.ToArray());
            }
            finally
            {
                g.Dispose();
                image.Dispose();
            }
        }
    }

使用：
<script language="javascript" type="text/javascript">
        function changeCode() {   
            var imgNode = document.getElementById("Image1");   
            imgNode.src = "../ValidateNum.aspx?t=" + (new Date()).valueOf(); 
 // 这里加个时间的参数是为了防止浏览器缓存的问题   
        } 
 </script>

<img ID="Image1" Height="22px" Width="48px" src="../ValidateNum.aspx" onclick="changeCode()" />

 

用户自定义控件

protected void CustomValidator1_ServerValidate(object source, ServerValidateEventArgs args)
    {
        if (txtValidateNum.Text.ToUpper().Trim() == Session["ValidateNum"].ToString())
        {
            args.IsValid = true;
        }
        else
            args.IsValid = false;
    }