高手来看看,我是菜鸟!

<%@ Page Language="C#" ContentType="text/html" ResponseEncoding="gb2312" %>
<%@ Import Namespace="System.Data" %>
<%@ Import Namespace="System.Data.OleDb" %> 
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=gb2312">
<title>无标题文档</title>
</head>
<body>
<script language="c#" runat="server">
string asdf;
public void btn_click(Object Sender,EventArgs e)
{string asdf=xls_file.Text;
Response.Write(asdf);
}
void Page_Load()
{
if (asdf!=null)
{
if (IsPostBack)
{
OleDbDataReader dr;
string sqlstr="Provider=Microsoft.Jet.OLEDB.4.0;Data Source=h:\\"+asdf+"; Extended Properties='Excel 8.0'";
 
OleDbConnection conn= new OleDbConnection(sqlstr);
conn.Open();
string xls_command="select * from [甘肃2$]";
OleDbCommand comm= new OleDbCommand(xls_command,conn);
dr=comm.ExecuteReader();
haha.DataSource=dr;
DataBind();
dr.Close();
conn.Close();}
}
else 
{Response.Write("唉....!!");}
}
</script>
<asp:DataGrid AllowPaging="false" CellPadding="6" CellSpacing="6" ID="haha" runat="server" ShowHeader="true"/>
<form runat="server">
<asp:TextBox ID="xls_file" runat="server"></asp:TextBox>
<asp:Button ID="btn" Text="提交查询" OnClick="btn_click" runat="server"></asp:Button>
</form>
</body>
</html>
请问如何在Page_Load()中取得asdf传过来的tb值?