标签未显示下拉列表选择的任何输出

Question

 SqlConnection con = new SqlConnection(ConfigurationManager.ConnectionStrings["LibraryConnectionString"].ConnectionString);

        protected void Page_Load(object sender, EventArgs e)
        {
            if (!IsPostBack)
            {
                ddlbookavail.Items.Add(new ListItem("select", "-1"));
                ddlbookavail.AppendDataBoundItems = true;
                SqlCommand cmd = new SqlCommand("select * from tblbookinfo", con);
                con.Open();
                ddlbookavail.DataSource = cmd.ExecuteReader(); 
                ddlbookavail.DataTextField = "Name";
                ddlbookavail.DataValueField = "Id";                               
                ddlbookavail.DataBind();            
                con.Close();
                txtdate.Text = DateTime.Now.Date.ToString("dd/MM/yyyy");
            }

在我的设计页面中，我从数据中输入了sql数据源并获得了此连接srting