ASP.NET ashx实现无刷新页面生成验证码

<div> <span>Identifying Code:</span> <asp:TextBox ID="txtValidationCode" runat="server" Width="130px" MaxLength="4"></asp:TextBox> <img id="imgYZ" class="code" style=" height:23px; width:65px;"   src="Img.ashx" onclick="this.src=this.src+'?'"/ /> <img src="../images/btn_change.gif" title="Change" class="btn_change" Style="cursor: hand"  onclick="ImgChange()" /></div>

<script language="javascript" type="text/javascript"> function ImgChange()  {   var img=document.getElementById("imgYZ");  img.click(); } </script>

using System;using System.Web;using CLAIMS.BLL;using System.Data;using System.Configuration;using System.Web.SessionState;using System.Drawing;public class Img : IHttpHandler, IRequiresSessionState{  public void ProcessRequest (HttpContext context)  {  context.Response.ContentType = "image/Jpeg";    string s_random = "";  System.IO.MemoryStream ms = new System.IO.MemoryStream();  s_random = RndNum(4);  context.Session["random"] = s_random;  s_random = s_random.Substring(0, 1) + " " + s_random.Substring(1, 1) + " " + s_random.Substring(2, 1) + " " + s_random.Substring(3, 1);    CreateImage(s_random, ref ms);  context.Response.ClearContent();  context.Response.BinaryWrite(ms.ToArray());  context.Response.Flush();  context.Response.End(); } private void CreateImage(string checkCode,ref System.IO.MemoryStream ms) {  int iwidth = (int)(checkCode.Length * 18);  System.Drawing.Bitmap image = new System.Drawing.Bitmap(iwidth, 45);  Graphics g = Graphics.FromImage(image);  g.Clear(Color.White);  //定义颜色  Color[] c = { Color.Black, Color.Red, Color.DarkBlue, Color.Green, Color.Orange, Color.Brown, Color.DarkCyan, Color.Purple };  //定义字体     //string[] font = {"Verdana","Microsoft Sans Serif","Comic Sans MS","Arial","宋体"};  Random rand = new Random();  //随机输出噪点  for (int i = 0; i < 50; i++)  {   int x = rand.Next(image.Width);   int y = rand.Next(image.Height);   g.DrawRectangle(new Pen(Color.LightGray, 0), x, y, 1, 1);  }  //输出不同字体和颜色的验证码字符  for (int i = 0; i < checkCode.Length; i++)  {   int cindex = rand.Next(7);   int findex = rand.Next(5);   Font font = new System.Drawing.Font("Arial", 24, (System.Drawing.FontStyle.Bold | System.Drawing.FontStyle.Italic));   Brush b = new System.Drawing.SolidBrush(c[cindex]);   int ii = 4;   if ((i + 1) % 2 == 0)   {    ii = 2;   }   g.DrawString(checkCode.Substring(i, 1), font, b, 3 + (i * 12), ii);  }  //画一个边框  g.DrawRectangle(new Pen(Color.Black, 0), 0, 0, image.Width - 1, image.Height - 1);  //输出到浏览器  image.Save(ms, System.Drawing.Imaging.ImageFormat.Jpeg);    g.Dispose();  image.Dispose(); } public static String RndNum(int VcodeNum) {  String Vchar = "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,W,X,Y,Z";  String[] VcArray = Vchar.Split(',');  String VNum = "";  Random random = new Random();  for (int i = 1; i <= VcodeNum; i++)  {   int iNum = 0;   while ((iNum = Convert.ToInt32(VcArray.Length * random.NextDouble())) == VcArray.Length)   {    iNum = Convert.ToInt32(VcArray.Length * random.NextDouble());   }   VNum += VcArray[iNum];  }  return VNum; }  public bool IsReusable {  get {   return false;  } }}