需要引入一个ashx的一般处理程序！
把这个程序在前台当作一个图片使用就可以！
前台代码：
<td> <img title="看不清？" style=" cursor:pointer ;vertical-align:middle" width="45px" src="../ValidateCode.ashx" onclick="this.src='../ValidateCode.ashx?_='+Math.random()" /> </td>
cursor:pointer 光标呈现为指示链接的指针（一只手）
onclick 点击切换图片
Math.random()随机数，改变切换地址，有些浏览器点击的时候不自动切换，直接调用缓存文件（如IE）
验证码一般处理程序ashx:
不知道为什么传不上来啊附件，我就把代码贴上来吧，大家回去用这个代码建立一个ashx的文件就OK了
建议验证码存到【session】里面，下面的代码是存到session里的（使用其他方法的可以注释掉context.Session["code"] = code;）
//一般处理程序中使用session，必须实现一个接口
首先添加一个命名空间“using System.Web.SessionState;”
我把我的后台登录的判断处代码贴到下面，也许对大家的理解有帮助。。。。
<%@ WebHandler Language="C#" Class="ValidateCode" %> using System; using System.Web; using System.Drawing; using System.Web.SessionState; public class ValidateCode : IHttpHandler, IRequiresSessionState { public void ProcessRequest(HttpContext context) { context.Response.ContentType = "image/jpeg"; string code = GetRndStr();//生成4个随机的字符 //记录生成的验证码到session context.Session["code"] = code; using (Bitmap img = CreateImages(code, "ch")) { img.Save(context.Response.OutputStream, System.Drawing.Imaging.ImageFormat.Jpeg); } } public bool IsReusable { get { return false; } } /// <summary> /// 数字随机数 /// </summary> /// <returns></returns> private string GetRndNum() { string code = string.Empty; Random random = new Random(); for (int i = 0; i < 4; i++) { code += random.Next(9); } return code; } /// <summary> /// 英文随机 /// </summary> /// <returns></returns> private string GetRndStr() { string Vchar = "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[] VcArray = Vchar.Split(','); string checkCode = string.Empty; Random rand = new Random(); for (int i = 0; i < 4; i++) { int t = rand.Next(VcArray.Length); checkCode += VcArray[t]; } return checkCode; } /// <summary> /// 中文随机 /// </summary> /// <returns></returns> private string GetRndCh() { System.Text.Encoding gb = System.Text.Encoding.Default;//获取GB2312编码页（表） object[] bytes = CreateRegionCode(4);//生4个随机中文汉字编码 string[] str = new string[4]; System.Text.StringBuilder sb = new System.Text.StringBuilder(); for (int i = 0; i < 4; i++) { //根据汉字编码的字节数组解码出中文汉字 str[i] = gb.GetString((byte[])Convert.ChangeType(bytes[i], typeof(byte[]))); sb.Append(str[i].ToString()); } return sb.ToString(); } /// <summary> /// 产生随机中文字符 /// </summary> /// <param name="strlength"></param> /// <returns></returns> private static object[] CreateRegionCode(int strlength) { //定义一个字符串数组储存汉字编码的组成元素 string[] rBase = new String[16] { "0", "1", "2", "3", "4", "5", "6", "7", "8", "9", "a", "b", "c", "d", "e", "f" }; Random rnd = new Random(); object[] bytes = new object[strlength]; for (int i = 0; i < strlength; i++) { //区位码第1位 int r1 = rnd.Next(11, 14); string str_r1 = rBase[r1].Trim(); //区位码第2位 rnd = new Random(r1 * unchecked((int)DateTime.Now.Ticks) + i); int r2; if (r1 == 13) { r2 = rnd.Next(0, 7); } else { r2 = rnd.Next(0, 16); } string str_r2 = rBase[r2].Trim(); //区位码第3位 rnd = new Random(r2 * unchecked((int)DateTime.Now.Ticks) + i);//更换随机种子 int r3 = rnd.Next(10, 16); string str_r3 = rBase[r3].Trim(); //区位码第4位 rnd = new Random(r3 * unchecked((int)DateTime.Now.Ticks) + i); int r4; if (r3 == 10) { r4 = rnd.Next(1, 16); } else if (r3 == 15) { r4 = rnd.Next(0, 15); } else { r4 = rnd.Next(0, 16); } string str_r4 = rBase[r4].Trim(); //定义两个字节变量存储产生的随机汉字区位码 byte byte1 = Convert.ToByte(str_r1 + str_r2, 16); byte byte2 = Convert.ToByte(str_r3 + str_r4, 16); //将两个字节变量存储在字节数组中 byte[] str_r = new byte[] { byte1, byte2 }; //将产生的一个汉字的字节数组放入object数组中 bytes.SetValue(str_r, i); } return bytes; } /// <summary> /// 画图片的背景图+干扰线 /// </summary> /// <param name="checkCode"></param> /// <returns></returns> private Bitmap CreateImages(string checkCode, string type) { int step = 0; if (type == "ch") { step = 5;//中文字符，边界值做大 } int iwidth = (int)(checkCode.Length * (13 + step)); System.Drawing.Bitmap image = new System.Drawing.Bitmap(iwidth, 33); Graphics g = Graphics.FromImage(image); g.Clear(Color.White);//清除背景色 Color[] c = { Color.Black, Color.Red, Color.DarkBlue, Color.Green, Color.Orange, Color.Brown, Color.DarkCyan, Color.Purple };//定义随机颜色 string[] font = { "Verdana", "Microsoft Sans Serif", "Comic Sans MS", "Arial", "宋体" }; Random rand = new Random(); for (int i = 0; i < 50; i++) { int x1 = rand.Next(image.Width); int x2 = rand.Next(image.Width); int y1 = rand.Next(image.Height); int y2 = rand.Next(image.Height); g.DrawLine(new Pen(Color.LightGray, 1), x1, y1, x2, y2);//根据坐标画线 } for (int i = 0; i < checkCode.Length; i++) { int cindex = rand.Next(7); int findex = rand.Next(5); Font f = new System.Drawing.Font(font[findex], 15, System.Drawing.FontStyle.Bold); Brush b = new System.Drawing.SolidBrush(c[cindex]); int ii = 4; if ((i + 1) % 2 == 0) { ii = 2; } g.DrawString(checkCode.Substring(i, 1), f, b, 3 + (i * (12 + step)), ii); } g.DrawRectangle(new Pen(Color.Black, 0), 0, 0, image.Width - 1, image.Height - 1); System.IO.MemoryStream ms = new System.IO.MemoryStream(); return image; } }
判断session后天代码：
protected void btnLogin_Click(object sender, EventArgs e) { //学生 1 老师 2 string type = ddl.SelectedValue; string no = txtNo.Text.Trim(); string pwd = txtPwd.Text.Trim(); //md5加密 pwd = Common.GetMd5(pwd); string code = txtCode.Text.Trim(); //验证码正确 因为session有过期失效的问题， //ps:session在服务器上默认保存20分钟 if (Session["code"] != null && code.ToLower() == Session["code"].ToString().ToLower()) { // Session.Remove("code"); string msg; //学生 if (type == "1") { //判断用户名密码是否正确 ItcastOCSS.BLL.Student bll = new ItcastOCSS.BLL.Student(); ItcastOCSS.Model.Student stu = new ItcastOCSS.Model.Student(); if (bll.Login(no, pwd, out msg, out stu)) { //记录登陆成功的状态 Session["user"] = stu; //跳转 Response.Redirect("Student/Index.aspx"); } lblMsg.Text = msg; } else if (type == "2") { //老师 ItcastOCSS.BLL.Teacher bll = new ItcastOCSS.BLL.Teacher(); ItcastOCSS.Model.Teacher tea = new ItcastOCSS.Model.Teacher(); if (bll.Login(no, pwd, out msg, out tea)) { Session["user"] = tea; //跳转 if (tea.TIsAdmin == 1) { //管理员 Response.Redirect("Admin/Index.aspx"); } else if(tea.TIsAdmin == 0) { //老师 Response.Redirect("Teacher/Index.aspx"); } } } } else { //验证码错误 lblMsg.Text = "验证码错误"; } }
另外一个
using System; using System.Collections.Generic; using System.Drawing; using System.Drawing.Drawing2D; using System.Drawing.Imaging; using System.IO; using System.Linq; using System.Text; using System.Threading.Tasks; using System.Web; namespace CZBK.ItcastProject.Common { public class ValidateCode { public ValidateCode() { } /// <summary> /// 验证码的最大长度 /// </summary> public int MaxLength { get { return 10; } } /// <summary> /// 验证码的最小长度 /// </summary> public int MinLength { get { return 1; } } /// <summary> /// 生成验证码 /// </summary> /// <param name="length">指定验证码的长度</param> /// <returns></returns> public string CreateValidateCode(int length) { int[] randMembers = new int[length]; int[] validateNums = new int[length]; string validateNumberStr = ""; //生成起始序列值 int seekSeek = unchecked((int)DateTime.Now.Ticks); Random seekRand = new Random(seekSeek); int beginSeek = (int)seekRand.Next(0, Int32.MaxValue - length * 10000); int[] seeks = new int[length]; for (int i = 0; i < length; i++) { beginSeek += 10000; seeks[i] = beginSeek; } //生成随机数字 for (int i = 0; i < length; i++) { Random rand = new Random(seeks[i]); int pownum = 1 * (int)Math.Pow(10, length); randMembers[i] = rand.Next(pownum, Int32.MaxValue); } //抽取随机数字 for (int i = 0; i < length; i++) { string numStr = randMembers[i].ToString(); int numLength = numStr.Length; Random rand = new Random(); int numPosition = rand.Next(0, numLength - 1); validateNums[i] = Int32.Parse(numStr.Substring(numPosition, 1)); } //生成验证码 for (int i = 0; i < length; i++) { validateNumberStr += validateNums[i].ToString(); } return validateNumberStr; } /// <summary> /// 创建验证码的图片 /// </summary> /// <param name="containsPage">要输出到的page对象</param> /// <param name="validateNum">验证码</param> public void CreateValidateGraphic(string validateCode, HttpContext context) { Bitmap image = new Bitmap((int)Math.Ceiling(validateCode.Length * 12.0), 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); //画图片的干扰线 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 Font("Arial", 12, (FontStyle.Bold | FontStyle.Italic)); //渐变. LinearGradientBrush brush = new LinearGradientBrush(new Rectangle(0, 0, image.Width, image.Height), Color.Blue, Color.DarkRed, 1.2f, true); g.DrawString(validateCode, font, brush, 3, 2); //画图片的前景干扰点 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); //保存图片数据 MemoryStream stream = new MemoryStream(); image.Save(stream, ImageFormat.Jpeg); //输出图片流 context.Response.Clear(); context.Response.ContentType = "image/jpeg"; context.Response.BinaryWrite(stream.ToArray()); } finally { g.Dispose(); image.Dispose(); } } /// <summary> /// 得到验证码图片的长度 /// </summary> /// <param name="validateNumLength">验证码的长度</param> /// <returns></returns> public static int GetImageWidth(int validateNumLength) { return (int)(validateNumLength * 12.0); } /// <summary> /// 得到验证码的高度 /// </summary> /// <returns></returns> public static double GetImageHeight() { return 22.5; } } }
本文转自：http://www.nbcoder.net/thread-337-1-1.html