Asp.net动态添加附件上传

<%@ Page language="c#" Codebehind="MultiAttchments.aspx.cs" AutoEventWireup="false" Inherits="WebApplication3.MultiAttchments" %>
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN" >
<HTML>
      <HEAD>
            <script>
            function AddAttachments()
            {
                  document.getElementById('attach').innerText = "继续添加附件";

                  tb = document.getElementById('attAchments');
                  newRow = tb.insertRow();
                  newRow.insertCell().innerHTML = "<input name='File' size='50' type='file'>  <input type=button value='删除' onclick='delFile(this.parentElement.parentElement.rowIndex)'>";
            }
            function delFile(index)
            {
                  document.getElementById('attAchments').deleteRow(index);
                  tb.rows.length > 0?document.getElementById('attach').innerText = "继续添加附件":document.getElementById('attach').innerText = "添加附件";
            }
            </script>
      </HEAD>
      <body MS_POSITIONING="GridLayout">

两种方式：
1、如果页面中form指定了enctype="multipart/form-data" 属性则可以无file服务器控件
2、如果页面上有初始的file服务器控件（必须有runat="server"标志）可以无enctype="multipart/form-data"属性，但是这个页面上必须至少有一个runat="server"的file控件，否则后台接收不equest.Files。

<%@ Page language="c#" Codebehind="MultiAttchments.aspx.cs" AutoEventWireup="false" Inherits="WebApplication3.MultiAttchments" %>
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN" >
<HTML>
      <HEAD>
            <script>
            function AddAttachments()
            {
                  document.getElementById('attach').innerText = "继续添加附件";
                 
                  tb = document.getElementById('attAchments');                 
                  newRow = tb.insertRow();
                  newRow.insertCell().innerHTML = "<input name='File' size='50' type='file'>&nbsp;&nbsp;<input type=button value='删除' onclick='delFile(this.parentElement.parentElement.rowIndex)'>";
            }
            function delFile(index)
            {
                  document.getElementById('attAchments').deleteRow(index);
                  tb.rows.length > 0?document.getElementById('attach').innerText = "继续添加附件":document.getElementById('attach').innerText = "添加附件";
            }
            </script>
      </HEAD>
      <body MS_POSITIONING="GridLayout">