gridview内实现文件下载

gridview内实现文件下载
实现起来有点迷惑性，用了几种方法，最后用a实现。

<%
  ...
  @ Page Language="C#" AutoEventWireup="true"  CodeFile="Default.aspx.cs" Inherits="_Default" 
  %>
  

  <!
  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 
  runat
  ="server"
  >
  
    
  <
  title
  >
  无标题页
  </
  title
  >
  
  </
  head
  >
  
  <
  body
  >
  
    
  <
  form 
  id
  ="form1"
   runat
  ="server"
  >
  
    
  <
  div
  >
  
        
  <
  asp:SqlDataSource 
  ID
  ="SqlDataSource1"
   runat
  ="server"
   
ConnectionString
  ="<%$ ConnectionStrings:testConnectionString %>"
  
            SelectCommand
  ="SELECT * FROM [files]"
  ></
  asp:SqlDataSource
  >
  
    
    
  </
  div
  >
  
        
  <
  asp:GridView 
  ID
  ="GridView1"
   runat
  ="server"
   AutoGenerateColumns
  ="False"
   
DataSourceID
  ="SqlDataSource1"
  >
  
            
  <
  Columns
  >
  
                
  <
  asp:BoundField 
  DataField
  ="id"
   HeaderText
  ="id"
   SortExpression
  ="id"
   
  />
  
                
  <
  asp:BoundField 
  DataField
  ="upload_file"
   HeaderText
  ="upload_file"
   
SortExpression
  ="upload_file"
   
  />
  
                
  <
  asp:BoundField 
  DataField
  ="file_name"
   HeaderText
  ="file_name"
   
ortExpression
  ="file_name"
   
  />
  
                
               
                
                
                 
  <
  asp:TemplateField
  ><
  ItemTemplate
  >
  
   
  <
  a 
  href
  ='<%#DataBinder.Eval(Container.DataItem,"file_name")%
  >
  ' target="_blank">下载
  </
  a
  >
   
   
  </
  Itemtemplate
  ></
  asp:TemplateField
  >
  
                
                
                
            
  </
  Columns
  >
  
        
  </
  asp:GridView
  >
  
       

       
    
  </
  form
  >
  
  </
  body
  >
  
  </
  html
  >