asp.net(c#)生成验证码

生成验证码,无非是把数字、字母或汉字混合在一起，生成图片，然后输出。这里用的是数字和字母。

首先，登陆界面需要显示这个图片，那么，就有：

<font color="#FF0000">请输入</font>            <img src="Validate.aspx" alt="" />

这个来显示图片，下面是Validate.aspx：

<%@ Page Language="C#" %><%@ import namespace="System"%><%@ import namespace="System.IO"%><%@ import namespace="System.Drawing"%><%@ import namespace="System.Drawing.Imaging"%><%@ import namespace="System.Drawing.Drawing2D"%>

<script runat="server">private Bitmap validateimage;private Graphics g;public void  Page_Load(object Sender,EventArgs e){     Response.BufferOutput = true;   //特别注意     Response.Cache.SetExpires(DateTime.Now.AddMilliseconds(-1));//特别注意     Response.Cache.SetCacheability(HttpCacheability.NoCache);//特别注意     Response.AppendHeader("Pragma", "No-Cache"); //特别注意    string  VNum  =MakeValidateCode( );    Session["VNum"]=VNum;//取得验证码，以便后来验证    ValidateCode(VNum);}public void ValidateCode(string VNum){validateimage = new Bitmap(60, 20, 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); //矩形框g.DrawString(VNum, new Font("arial",11),new SolidBrush(Color.Red),new PointF(6,0));//字体/颜色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'};//枚举数组string num = "";Random r = new Random();for(int i = 0; i < 5; i++){num += s[r.Next(0, s.Length)].ToString(); } return num;}</script>，那显示出来之后，用户输入到文本框，提交，就需要检验一下验证码是否正确，在login.aspx.cs中：

            if (checkcode == Session["VNum"].ToString() || Session["VNum"].ToString() == null) { }//注意Session["VNum"].ToString()，必须加上ToString()，因//为Session["VNum"]是对象。            //要做的事情            else            {                Message.Text = "验证码错误或为空！";                founderr = true;            }

这样，就完成了 验证码的生成以及验证。