how to bind data in ListItem in dropdownlist

 <asp:DropDownList ID="DropDownList1" runat="server">
        </asp:DropDownList>

 SqlConnection objcon = new SqlConnection(".........");
        objcon.Open();
        SqlCommand objcmd = new SqlCommand("select * from Tablename", objcon);
        SqlDataReader objreader = objcmd.ExecuteReader();
        objreader.Read();
        {
            DropDownList1.Items.Add(new ListItem(objreader.GetString(1)));
        }