asp net如何让后台代码控制div层显示及隐藏
前台JS
 <style type="text/css"> 
  * {margin:0;padding:0;font-size:12px;} 
  html,body {height:100%;width:100%;} 
  #content {background:#f8f8f8;padding:30px;height:100%;} 
  #content a {font-size:30px;color:#369;font-weight:700;} 
  #alert {border:1px solid #369;width:260px;height:90px;background:#e2ecf5;z-index:1000;position:absolute;display:none;} 
  #alert h4 {height:20px;background:#369;color:#fff;padding:5px 0 0 5px;} 
  #alert h4 span {float:left;} 
  #alert h4 span#close {margin-left:210px;font-weight:500;cursor:pointer;} 
  #alert p {padding:12px 0 0 30px;} 
  #alert p input {width:120px;margin-left:20px;} 
  #alert p input.myinp {border:1px solid #ccc;height:16px;} 
  #alert p input.sub {width:60px;margin-left:30px;} 
  </style>

 <div id="alert" style="text-align:center " > 
  <h4><span>系统提示</span></h4> 
  <table>
  <tr>
  <td colspan="3" style="height:14px"></td>
  </tr>
  <tr>
  <td style="width:10%"></td>
  <td style="text-align:right"> <img alt="a" src="../Image/13221820.gif" /></td>
  <td style="text-align:left">短信正在发送中,请不要关闭网页! </td>
  </tr>
  </table>
  </div> 
  <script type="text/ecmascript">
  var myAlert = document.getElementById("alert");

  function show() {
  myAlert.style.display = "block";
  myAlert.style.position = "absolute";
  myAlert.style.top = "50%";
  myAlert.style.left = "50%";
  myAlert.style.marginTop = "-75px";
  myAlert.style.marginLeft = "-150px";
  document.body.style.overflow = "hidden";
  }
   
  </script>
  <script type="text/javascript">

  function close() {
  myAlert.style.display = "none";
  } 
  </script>

后台按钮事件中的代码：
  if (TextBox1.Text.Trim() == "" || TextBox2.Text.Trim() == "")
  {
  Page.RegisterStartupScript("f","<script>alert('不能为空');</script>");
  return;
  }
  Page.RegisterStartupScript("", "<script> show() ;</script>");//正常弹出
  // Page.RegisterStartupScript("show", "<script> show() ;</script>"); 当key不为空字符串的时候，DIV不能弹出



  for (int i = 0; i < 10000; i++)
  {
  if (i == 9999)
  {
  Page.RegisterStartupScript("", "<script>close();</script>");//DIV不能隐藏
  //Page.RegisterStartupScript("close", "<script>close();</script>");DIV不能正常弹出
  Page.RegisterStartupScript("d", "<script>alert('ok');</script>");