dynamically populate dropdownlist

i m using following code to populate dropdownlist dynamically... i want that value should be the subject id and text should be the sub_desc...but code is not working the value does not contain the sub_ids...so whats wrong with the code??

(sub_id is integer field)

 public void Populate()
        {
            string ConnectionString = (string)ConfigurationManager.AppSettings["ConnectionString"];
         SqlConnection conn = new SqlConnection(ConnectionString);
            SqlCommand popCmd = new SqlCommand("select sub_id,sub_desc from subject", conn);
            try
            {
                conn.Open();
                ddlSub.Items.Clear();

                SqlDataReader subs;
                subs = popCmd.ExecuteReader();


                ddlSub.DataSource = subs;
                ddlSub.DataValueField = "sub_id";
                ddlSub.DataTextField = "sub_des开发者_StackOverflowc";
                ddlSub.DataBind();
                conn.Close();
            }
            catch (Exception ex)
            {
               lblMsg.Visible = true;
               lblMsg.Text = ex.ToString();

            }

        }

thanx...

---

You can set AppendDataBoundItems="true" to ensure data bound items do not clear manually inserted list items.

<asp:DropDownList ID="DropDownList" runat="server" AppendDataBoundItems="true">
    <asp:ListItem Value="--Select Subject--" Text="--Select Subject--" Selected="true"></asp:ListItem>
</asp:DropDownList>

You can also accomplish this in the code behind.

...
dropSub.Items.Add(new ListItem("--Select Subject--", "0"));
dropSub.AppendDataBoundItems = true;
SqlDataReader subs;
subs = popCmd.ExecuteReader();
ddlSub.DataSource = subs;
ddlSub.DataValueField = "sub_id";
ddlSub.DataTextField = "sub_desc";
ddlSub.DataBind();
conn.Close();
...

---

You can add you default after databinding. You will need to insert at an index of 0 though rather than Add.