task: to retrieve data from access file to textbox1 on button click

using System;
using System.Configuration;
using System.Data;
using System.Data.OleDb;
using System.Linq;
using System.Web;
using System.Web.Security;
using System.Web.UI;
using System.Web.UI.HtmlControls;
using System.Web.UI.WebControls;
using System.Web.UI.WebControls.WebParts;
using System.Xml.Linq;

public partial class _Default : System.Web.UI.Page 
{
    OleDbConnection conn = new OleDbConnection("Provider=Microsoft.Jet.OLEDB.4.0;Data Source=C:/Documents and Settings/abby1/My Documents/Visual Studio 2008/WebSites/WebSite3/App_Data/TEST.mdb");
    OleDbDataReader rdr = null;
    protected void Page_Load(object sender, EventArgs e)
    {

    }
    protected void TextBox1_TextChanged(object sender, EventArgs e)
    {
       
    }
    protected void Button1_Click(object sender, EventArgs e)
    {
        try
        {        
            conn.Open();
            OleDbCommand str = new OleDbCommand("select appno from final", conn);           
            OleDbDataReader rdr = str.ExecuteReader();
            DataSet ds = new DataSet();
            if (rdr.HasRows)
            {
                while (rdr.Read())
                {
                    if (rdr.Read())
                    {
                        TextBox1.Text = rdr.GetValue(0).ToString();
                    }
                    s = dr.GetData();
                    TextBox1.Text = Convert.ToString(str);
                }
            }
        }
        catch
        {
            conn.Close();
        }
    }

    private string ToString(string p)
    {
        throw new NotImplementedException();
    }
}