上传控件的奇怪问题

  
    

   
     1 
   
     <
   
     iframe id
   
     =
   
     "
   
     file_upload
   
     "
   
      runat
   
     =
   
     "
   
     server
   
     "
   
      frameborder
   
     =
   
     "
   
     0
   
     "
   
      scrolling
   
     =
   
     "
   
     no
   
     "
   
      src
   
     =
   
     "
   
     ../upload_file.aspx
   
     "
   
      style
   
     =
   
     "
   
     width: 100%; height: 25px
   
     "
   
     ></
   
     iframe
   
     >
   
     

   
     2 
   
      
   
     <
   
     input id
   
     =
   
     "
   
     pic_path
   
     "
   
      type
   
     =
   
     "
   
     hidden
   
     "
   
      runat
   
     =
   
     "
   
     server
   
     "
   
      
   
     />
   
      
  
    

我最近做的项目里都需要用到这个控件。 之前一直都是

  
    

   
     <
   
     script type
   
     =
   
     "
   
     text/javascript
   
     "
   
     >
   
     
 function $(obj) {
 
   
     return
   
      document.getElementById(obj);
 }
 function setPicValue() {
 var doc 
   
     =
   
      $(
   
     "
   
     file_upload
   
     "
   
     ).contentWindow.document;
 $(
   
     "
   
     pic_path
   
     "
   
     ).value 
   
     =
   
      doc.getElementById(
   
     "
   
     file_url
   
     "
   
     ).innerHTML;
 var doc1 
   
     =
   
      $(
   
     "
   
     file_upload1
   
     "
   
     ).contentWindow.document;
 $(
   
     "
   
     pic_path1
   
     "
   
     ).value 
   
     =
   
      doc1.getElementById(
   
     "
   
     file_url
   
     "
   
     ).innerHTML;
 var doc2 
   
     =
   
      $(
   
     "
   
     file_upload2
   
     "
   
     ).contentWindow.document;
 $(
   
     "
   
     pic_path2
   
     "
   
     ).value 
   
     =
   
      doc2.getElementById(
   
     "
   
     file_url
   
     "
   
     ).innerHTML;
 var doc3 
   
     =
   
      $(
   
     "
   
     file_upload3
   
     "
   
     ).contentWindow.document;
 $(
   
     "
   
     pic_path3
   
     "
   
     ).value 
   
     =
   
      doc3.getElementById(
   
     "
   
     file_url
   
     "
   
     ).innerHTML;
 var doc4 
   
     =
   
      $(
   
     "
   
     file_upload4
   
     "
   
     ).contentWindow.document;
 $(
   
     "
   
     pic_path4
   
     "
   
     ).value 
   
     =
   
      doc4.getElementById(
   
     "
   
     file_url
   
     "
   
     ).innerHTML;
 
 }
 
   
     </
   
     script
   
     >
  
    

用这个function在提交按钮的OnClientClick事件中调用。一直没有出现问题。 但是今天后台怎么都拿不到pic_path的值。 一位高手告诉我说是因为File的安全机制问题。 提交的时候把File的值清空了。 但我在后台监视Request.Form的时候发现

  
    

   
     Request.Form[
   
     "
   
     pic_path
   
     "
   
     ]
  
    

这样子可以拿到值。  很让人费解。。 有谁深究过这个问题的  给解答一下