验证码的使用

后台代码：CheckCode.aspx

using System;

using System.Data;

using System.Configuration;

using System.Collections;

using System.Web;

using System.Web.Security;

using System.Web.UI;

using System.Web.UI.WebControls;

using System.Web.UI.WebControls.WebParts;

using System.Web.UI.HtmlControls;

using System.IO;

using System.Drawing;

using System.Drawing.Imaging;

using System.Drawing.Drawing2D;

public partial class Admin_CheckCode : System.Web.UI.Page

{

private Bitmap validateimage;

private Graphics g;

protected void Page_Load(object sender, EventArgs e)

{

if (!IsPostBack)

{

string VNum = MakeValidateCode();

Session["VNum"] = VNum;

ValidateCode(VNum);

}

}

public void ValidateCode(string VNum)

{

validateimage = new Bitmap(60, 15, PixelFormat.Format24bppRgb);

g = Graphics.FromImage(validateimage);

g.FillRectangle(new LinearGradientBrush(new Point(0, 0), new Point(110, 20), Color.FromArgb(240, 255, 255, 255), Color.FromArgb(240, 255, 255, 255)), 0, 0, 200, 200);

g.DrawString(VNum, new Font("arial", 11), new SolidBrush(Color.Red), new PointF(6, 0));

g.Save();

MemoryStream ms = new MemoryStream();

validateimage.Save(ms, System.Drawing.Imaging.ImageFormat.Gif);

Response.ClearContent();

Response.ContentType = "image/bmp";

Response.BinaryWrite(ms.ToArray());

Response.End();

}

string MakeValidateCode()

{

char[] s = new char[]{'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 num = "";

Random r = new Random();

for (int i = 0; i < 4; i++)

{

num += s[r.Next(0, s.Length)].ToString();

}

return num;

}

}

在Login.aspx前台应用：<img src="CheckCode.aspx" id="yzm" onclick="this.src='CheckCode.aspx?abc='+Math.random()" alt="图片看不清？点击重新得到验证码" style="cursor:hand;" />

在Login.aspx.cs中通过if (TextBox1.Text != Session["VNum"].ToString().ToLower())判断客户输入的验证吗是否正确。