ASP.NET验证码示例

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<%@ Page Language="C#" %>
<%@ Import Namespace="System.Drawing" %>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">

<script runat="server">
        /// <summary>
        /// 输入要求的验证码的位数，返回一个验证码字符串
        /// </summary>
        /// <param name="codeCount">验证码的位数</param>
        /// <returns>验证码字符串</returns>
        private string CreateRandomCode(int codeCount)
        {
            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,V,W,X,Y,Z," +
                "a,b,c,d,e,f,g,h,i,j,k,l,m,n,o,p,q,r,s,t,u,v,w,x,y,z";
            string[] allCharArray = allChar.Split(',');
            int allCharLen = allCharArray.Length;
            string randomCode = "";

            Random rand = new Random();
            for (int i = 0; i < codeCount; i++)
            {
                randomCode += allCharArray[rand.Next(0, allCharLen)];
            }
            return randomCode;
        }

        /// <summary>
        /// 根据验证码checkCode画图
        /// </summary>
        /// <param name="checkCode"></param>
        private void CreateImage(string checkCode)
        {
            int iwidth = (int)(checkCode.Length * 11.5);
            System.Drawing.Bitmap image = new System.Drawing.Bitmap(iwidth, 20);
            Graphics g = Graphics.FromImage(image);
            Font f = new System.Drawing.Font("Arial", 10, System.Drawing.FontStyle.Bold);
            Brush b = new System.Drawing.SolidBrush(Color.White);
            //g.FillRectangle(new System.Drawing.SolidBrush(Color.Blue),0,0,image.Width, image.Height);
            g.Clear(Color.Blue);
            g.DrawString(checkCode, f, b, 3, 3);
            g.Dispose();

            //Pen blackPen = new Pen(Color.Black, 0);
            //Random rand = new Random();
            //for (int i = 0; i < 5; i++)
            //{
            //    int y = rand.Next(image.Height);
            //    g.DrawLine(blackPen, 0, y, image.Width, y);
            //}

            System.IO.MemoryStream ms = new System.IO.MemoryStream();
            image.Save(ms, System.Drawing.Imaging.ImageFormat.Jpeg);
            Response.ClearContent();
            Response.ContentType = "image/Jpeg";
            Response.BinaryWrite(ms.ToArray());
            image.Dispose();
            //---------缓存验证码，以备验证---------
            Session["ValidateCode"] = checkCode;
            /*如果希望在挂接该aspx页的页面A.aspx内执行Session的绑定就是白扯！
             * A页面首先绑定，然后是确定表达式，此时B.aspx未执行，还没有产生Session呢！
             * */
        }
        protected void Page_Load(object sender, EventArgs e)
        {
            CreateImage(CreateRandomCode(6));
        }
</script>

<html xmlns="http://www.w3.org/1999/xhtml" >
<head id="Head1" runat="server">
    <title>无标题页</title>
</head>
<body>
</body>
</html>

调用上面的验证程序：

<%@ Page Language="C#" %>

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">

<script runat="server">
    protected void btnSend_Click(object sender, EventArgs e)
    {
        if(Session["ValidateCode"].ToString()!=txtValidateCode.Text)
        Response.Write("验证码不正确");
        else
        Response.Write("登录到新的界面！");
    }
</script>

<html xmlns="http://www.w3.org/1999/xhtml" >
<head id="Head1" runat="server">
    <title>无标题页</title>

</head>
<body>
    <form id="form1" runat="server">
        <div>
        <asp:TextBox ID="txtValidateCode" runat="server"></asp:TextBox>

        <img src="ValidateCode.aspx" alt="验证码" />
        <br />
        <asp:Button ID="btnSend" runat="server" OnClick="btnSend_Click" Text="发送" /></div>
    </form>
</body>
</html>