asp.net 调用window.print执行打印

<%@ Page language="c#" Codebehind="WPrint.aspx.cs" AutoEventWireup="false" Inherits="ASPNETPrint._01WindowPrint.WPrint" %>
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN" >
<HTML>
<HEAD>
   <title>WebForm1</title>
   <meta name="GENERATOR" Content="Microsoft Visual Studio 7.0">
   <meta name="CODE_LANGUAGE" Content="C#">
   <meta name="vs_defaultClientScript" content="JavaScript">
   <meta name="vs_targetSchema" content="http://schemas.microsoft.com/intellisense/ie5">
   <script language="javascript">
   function preview()
   {
   bdhtml=window.document.body.innerHTML;
   sprnstr="";
   eprnstr="";    //打印两者之间的内容
   prnhtml=bdhtml.substr(bdhtml.indexOf(sprnstr)+17);
   prnhtml=prnhtml.substring(0,prnhtml.indexOf(eprnstr));
   window.document.body.innerHTML=prnhtml;
   window.print();
   }
   </script>
</HEAD>
<body MS_POSITIONING="GridLayout">
   <form id="WebForm1" method="post" runat="server">
    <center>本部分以上不被打印</center>
    
    <div align="center">
     <asp:DataGrid id="dgShow" runat="server" BorderColor="#CC9966" BorderStyle="None" BorderWidth="1px" BackColor="White" CellPadding="4">
      <SelectedItemStyle Font-Bold="True" ForeColor="#663399" BackColor="#FFCC66"></SelectedItemStyle>
      <ItemStyle ForeColor="#330099" BackColor="White"></ItemStyle>
      <HeaderStyle Font-Bold="True" ForeColor="#FFFFCC" BackColor="#990000"></HeaderStyle>
      <FooterStyle ForeColor="#330099" BackColor="#FFFFCC"></FooterStyle>
      <PagerStyle HorizontalAlign="Center" ForeColor="#330099" BackColor="#FFFFCC"></PagerStyle>
     </asp:DataGrid>
    </div>
    
    <center>本部分以下不被打印</center>
    <div align="center">
     <input type="button" name="print" value="预览并打印" onclick="preview()"> 　//打印按钮
    </div>
    <style> @media Print { .Noprn { DISPLAY: none }}
    </style>
    <p class="Noprn">不打印</p>　　　//Noprn之间的内容不打印
    <table id="datagrid">
     <tr>
      <td>打印</td>
     </tr>
    </table>
    <input class="Noprn" type="button" onclick="window.print()" value="print">
   </form>
</body>
</HTML>