效果：
思路：
借用ashx文件创建四位验证，首先生成四位随机数字。然后创建画布，再将创建好的验证码存入session,然后前台进行button按钮将文本框中的值进行ajax请求到后台，和session中的验证码进行对比，成功返回true,失败返回false.
代码：
【前台】
1 <%@ Page Language="C#" AutoEventWireup="true" CodeBehind="verifycodeDemo.aspx.cs" Inherits="verifycodeDemo.verifycodeDemo" %> 2 3 <!DOCTYPE html> 4 5 <html xmlns="http://www.w3.org/1999/xhtml"> 6 <head runat="server"> 7 <meta http-equiv="Content-Type" content="text/html; charset=utf-8" /> 8 <title>青苹果验证码例子</title> 9 <script src="jquery-1.3.2.min.js"></script> 10 <script type="text/javascript"> 11 //切换验证码 12 function ToggleCode(obj, codeurl) { 13 $("#" + obj).attr("src", codeurl + "?time=" + Math.random()); 14 } 15 //ajax提交后台验证 16 function postAjax() { 17 var VerifyCodeValue = $("#txtVerifyCode").val(); 18 $.ajax({ 19 type: 'post', 20 dataType: "text", 21 url: "verifycodeDemo.aspx", 22 data: "action=comparison&VerifyCode=" + VerifyCodeValue, 23 cache: false, 24 async: false, 25 success: function (msg) { 26 if (msg == "false") { 27 alert("验证失败!sorry,青苹果"); 28 ToggleCode("Verify_codeImag", "VerifyCode.ashx"); 29 $("#txtVerifyCode").val(""); 30 } 31 else { 32 alert("验证成功！hello,青苹果!"); 33 } 34 } 35 }); 36 } 37 </script> 38 </head> 39 <body> 40 <form id="form1" runat="server"> 41 <div> 42 <input type="text" id="txtVerifyCode" /> 43 <img src="VerifyCode.ashx" id="Verify_codeImag" alt="点击切换验证码" style="CURSOR: pointer" width="65" height="25" title="点击切换验证码" onclick="ToggleCode(this.id, 'VerifyCode.ashx');return false;" /> 44 <input type="button" value="青苹果验证码" onclick="postAjax()" /> 45 </div> 46 </form> 47 </body> 48 </html>
【后台】
1 using System; 2 using System.Collections.Generic; 3 using System.Linq; 4 using System.Web; 5 using System.Web.UI; 6 using System.Web.UI.WebControls; 7 8 namespace verifycodeDemo 9 { 10 public partial class verifycodeDemo : System.Web.UI.Page 11 { 12 protected void Page_Load(object sender, EventArgs e) 13 { 14 string action = Request.Params["action"]; 15 string VerifyCodeValue = Request.Params["VerifyCode"]; 16 if (action == "comparison") 17 { 18 string Msg = "true"; 19 //对session中存储的验证码对比 20 if (HttpContext.Current.Session["dt_session_code"] == null || VerifyCodeValue.ToLower() != HttpContext.Current.Session["dt_session_code"].ToString().ToLower()) 21 { 22 Msg = "false";//验证码输入不正确 23 } 24 Response.Write(Msg); 25 Response.End(); 26 } 27 28 } 29 } 30 }
【ashx文件】
1 using System; 2 using System.Collections.Generic; 3 using System.Drawing; 4 using System.Drawing.Imaging; 5 using System.IO; 6 using System.Linq; 7 using System.Web; 8 using System.Web.SessionState; 9 10 11 namespace ESoftMS.Web.Frame 12 { 13 /// <summary> 14 /// VerifyCode 的摘要说明 青苹果(www.cnblogs.com/xinchun) 15 /// </summary> 16 public class VerifyCode : IHttpHandler, IRequiresSessionState 17 { 18 19 public void ProcessRequest(HttpContext context) 20 { 21 int codeW = 80; 22 int codeH = 22; 23 int fontSize = 16; 24 string chkCode = string.Empty; 25 //颜色列表，用于验证码、噪线、噪点 26 Color[] color = { Color.Black, Color.Red, Color.Blue, Color.Green, Color.Orange, Color.Brown, Color.Brown, Color.DarkBlue }; 27 //字体列表，用于验证码 28 string[] font = { "Times New Roman", "Verdana", "Arial", "Gungsuh", "Impact" }; 29 //验证码的字符集，去掉了一些容易混淆的字符 30 char[] character = { '2', '3', '4', '5', '6', '8', '9', 'a', 'b', 'd', 'e', 'f', 'h', 'k', 'm', 'n', 'r', 'x', 'y', 'A', 'B', 'C', 'D', 'E', 'F', 'G', 'H', 'J', 'K', 'L', 'M', 'N', 'P', 'R', 'S', 'T', 'W', 'X', 'Y' }; 31 Random rnd = new Random(); 32 //生成验证码字符串 33 for (int i = 0; i < 4; i++) 34 { 35 chkCode += character[rnd.Next(character.Length)]; 36 } 37 //写入Session 38 context.Session["dt_session_code"] = chkCode; 39 //创建画布 40 Bitmap bmp = new Bitmap(codeW, codeH); 41 Graphics g = Graphics.FromImage(bmp); 42 g.Clear(Color.White); 43 //画噪线 44 for (int i = 0; i < 1; i++) 45 { 46 int x1 = rnd.Next(codeW); 47 int y1 = rnd.Next(codeH); 48 int x2 = rnd.Next(codeW); 49 int y2 = rnd.Next(codeH); 50 Color clr = color[rnd.Next(color.Length)]; 51 g.DrawLine(new Pen(clr), x1, y1, x2, y2); 52 } 53 //画验证码字符串 54 for (int i = 0; i < chkCode.Length; i++) 55 { 56 string fnt = font[rnd.Next(font.Length)]; 57 Font ft = new Font(fnt, fontSize); 58 Color clr = color[rnd.Next(color.Length)]; 59 g.DrawString(chkCode[i].ToString(), ft, new SolidBrush(clr), (float)i * 18 + 2, (float)0); 60 } 61 ////画噪点 62 //for (int i = 0; i < 1; i++) 63 //{ 64 // int x = rnd.Next(bmp.Width); 65 // int y = rnd.Next(bmp.Height); 66 // Color clr = color[rnd.Next(color.Length)]; 67 // bmp.SetPixel(x, y, clr); 68 //} 69 //清除该页输出缓存，设置该页无缓存 70 context.Response.Buffer = true; 71 context.Response.ExpiresAbsolute = System.DateTime.Now.AddMilliseconds(0); 72 context.Response.Expires = 0; 73 context.Response.CacheControl = "no-cache"; 74 context.Response.AppendHeader("Pragma", "No-Cache"); 75 //将验证码图片写入内存流，并将其以 "image/Png" 格式输出 76 MemoryStream ms = new MemoryStream(); 77 try 78 { 79 bmp.Save(ms, ImageFormat.Png); 80 context.Response.ClearContent(); 81 context.Response.ContentType = "image/Gif"; 82 context.Response.BinaryWrite(ms.ToArray()); 83 } 84 catch (Exception) 85 { 86 87 } 88 finally 89 { 90 g.Dispose(); 91 bmp.Dispose(); 92 } 93 } 94 95 public bool IsReusable 96 { 97 get 98 { 99 return false; 100 } 101 } 102 } 103 }
Demo下载：