asp.net在页面提交时，显示提交中loading

asp.net|loading|显示|页面

<div id="doing" runat="server" style="Z-INDEX: 12000; LEFT: 0px; WIDTH: 100%; CURSOR: wait; POSITION: absolute; TOP: 0px; HEIGHT: 100%">
<table width="100%" height="100%">
<tr align="middle" valign="center">
<td>
<table width="169" height="62" bgcolor="#99cccc" style="FILTER: Alpha(Opacity=75); WIDTH: 169px; HEIGHT: 62px">
<tr align="middle" valign="center">
<td>页面提交中.<br>
Loading.</td>
</tr>
</table>

</td>
</tr>
</table>
</div>

private void Page_Load(object sender, System.EventArgs e)
  {
   // 在此处放置用户代码以初始化页面
   this.Button1.Attributes.Add("onclick","javascript:document.getElementById('doing').style.visibility='visible';");
  
   }

override protected void OnPreRender(EventArgs e)
  {
   doing.Style.Add("visibility","hidden");
  }