c#文件上传 如何调试AjaxuploadHandler.ashx

html:<%@ Page Language="C#" AutoEventWireup="true" CodeBehind="ImageTest.aspx.cs" Inherits="WebUI.ImageTest" %>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<meta http-equiv="Content-Type" content="text/html;charset=utf-8" />
<title>jquery实现按钮上传作者</title>
  <style type="text/css">        
   #txtFileName { width: 300px;}        
    .btnsubmit{
    border-bottom: #cc4f00 1px solid;
    border-left: #ff9000 1px solid;
    border-top: #ff9000 1px solid;  
    border-right: #cc4f00 1px solid;
    text-align: center;
    padding: 2px 10px;
    line-height: 16px;
    background: #e36b0f; 
    height: 24px;
    color: #fff;
    font-size: 12px;
    cursor: pointer;
    }     
    </style> 
  <script type="text/javascript" src="js/jquery-1.4.min.js"></script>
  <script type="text/javascript" src="js/ajaxupload.js"></script>
  <script type="text/javascript">
      //支持图片格式png/jpg/gif/jpeg，文件大小不能超过500KB。
      $(function () {
          var button = $('#btnUp'), interval;
          new AjaxUpload(button, {
              //action:'upload-test.php',文件上传服务器端执行的地址 
              action: 'AjaxuploadHandler.ashx',
              name: 'myfile',
              onSubmit: function (file, ext) {
                  if (!(ext && /^(jpg|jpeg|JPG|JPEG|gif|GIF|png|PNG)$/.test(ext))) {
                      alert('图片格式不正确,请选择正确格式的文件!', '系统提示');
                      return false;
                  }
                  button.text('上传中');
                  this.disable();
                  interval = window.setInterval(function () {
                      var text = button.text();
                      if (text.length < 10) {
                          button.text(text + '|');
                      } else {
                          button.text('上传中');
                      }
                  }, 200);
              },
              onComplete: function (file, response) {
                  //file 本地文件名称，response 服务器端传回的信息 
                  //button.text('上传图片(只允许上传JPG格式的图片,大小不得大于500K)' );
                  // button.text('重新上传' );
                  window.clearInterval(interval);
                  this.enable();
                  var k = response.replace("<PRE>", "").replace("</PRE>", "");
                  if (k == '-1') {
                      alert('您上传的文件太大啦!请不要超过500K');
                  }
                  else {
                      //  alert( "服务器端传回的串：" +k);
                      // alert( "本地文件名称：" +file);
                      $("#txtFileName").val(k);
                      $("<img />").appendTo($('#imglist')).attr("src", k);
                  }
              }
          });
      });
     
</script> 
</head><body>上传图片：<input type="text" id="txtFileName" />
          <div  id="btnUp" style="width:300px;" class="btnsubmit" >浏览</div> 
          <div id="imglist"></div>
</body>
</html>
c# 代码
using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Web.UI;
using System.Web.UI.WebControls;using System.Text.RegularExpressions;
using System.IO;using System.Text;public class UploadHandler : IHttpHandler
{
    private string _filedir = "";    //文件目录   
    /// <summary>   
    /// 处理上传文件(1:文件格式不正确、2:文件大小不正确、3:上传失败、文件名称:上传成功)   
    /// </summary>   
    /// <param name="context"></param>   
    public void ProcessRequest(HttpContext context)
    {        
        try
        {
            string result = "3";
           // string fileType = context.Request.QueryString["fileType"]; //获取上传文件类型  
            string fileType = "img";
            if (fileType == "file")
            {
                result = UploadFile(context);  //文档上传   
            }
            else if (fileType == "img")
            {
                result = UploadImg(context);   //图片上传   
            }
            context.Response.Write(result);
        }
        catch
        {
            context.Response.Write("3");//3文件上传失败   
        }
    }    #region   文档上传
    /// <summary>   
    /// 文档上传   
    /// </summary>   
    /// <param name="context"></param>   
    /// <returns></returns>   
    private string UploadFile(HttpContext context)
    {
        int cout = context.Request.Files.Count;
        if (cout > 0)
        {
            HttpPostedFile hpf = context.Request.Files[0];
            if (hpf != null)
            {
                string fileExt = Path.GetExtension(hpf.FileName).ToLower();
                //只能上传文件，过滤不可上传的文件类型     
                string fileFilt = ".rar|.zip|.pdf|.pdfx|.txt|.csv|.xls|.xlsx|.doc|.docx";
                if (fileFilt.IndexOf(fileExt) <= -1)
                {
                    return "1";
                }                //判断文件大小     
                int length = hpf.ContentLength;
                if (length > 2097152)
                {
                    return "2";
                }                Random rd = new Random();
                DateTime nowTime = DateTime.Now;
                string newFileName = nowTime.Year.ToString() + nowTime.Month.ToString() + nowTime.Day.ToString() + nowTime.Hour.ToString() + nowTime.Minute.ToString() + nowTime.Second.ToString() + rd.Next(1000, 1000000) + Path.GetExtension(hpf.FileName);
                if (!Directory.Exists(_filedir))
                {
                    Directory.CreateDirectory(_filedir);
                }
                string fileName = _filedir + newFileName;
                hpf.SaveAs(fileName);
                return newFileName;
            }        }
        return "3";
    }
    #endregion    /// <summary>   
    /// 图片上传   
    /// </summary>   
    /// <param name="context"></param>   
    /// <returns></returns>   
    private string UploadImg(HttpContext context)
    {
        string date = DateTime.Now.Year.ToString() + DateTime.Now.Month.ToString() + DateTime.Now.Day.ToString();        //_filedir = context.Server.MapPath(@"\\192.168.0.222\E:\upload");
        _filedir = context.Server.MapPath(@"E:\upload");
        
        int cout = context.Request.Files.Count;
        if (cout > 0)
        {
            HttpPostedFile hpf = context.Request.Files[0];
            if (hpf != null)
            {
                string fileExt = Path.GetExtension(hpf.FileName).ToLower();
                //只能上传文件，过滤不可上传的文件类型     
                
                string fileFilt = ".gif|.jpg|.bmp|.jpeg|.png";
                if (fileFilt.IndexOf(fileExt) <= -1)
                {
                    return "1";
                }                //判断文件大小     
                int length = hpf.ContentLength;
                if (length > 204800)
                {
                    return "2";
                }                Random rd = new Random();
                DateTime nowTime = DateTime.Now;
                string newFileName = nowTime.Year.ToString() + nowTime.Month.ToString() + nowTime.Day.ToString() + nowTime.Hour.ToString() + nowTime.Minute.ToString() + nowTime.Second.ToString() + rd.Next(1000, 1000000) + Path.GetExtension(hpf.FileName);
                if (!Directory.Exists(_filedir))
                {
                    Directory.CreateDirectory(_filedir);
                }
                string fileName = _filedir + newFileName;
                hpf.SaveAs(fileName);
                return newFileName;
            }
        }
        return "3";
    }
        #region IHttpHandler 成员    public bool IsReusable
    {
        get { throw new NotImplementedException(); }
    }    #endregion
}
没有任何反应。哪里错了。也不知道如何调试