How to bind dropdown on change of CalendarExtender dates

protected void TextBox2_TextChanged(object sender, EventArgs e)
    {
        SqlConnection con = new SqlConnection(@"Data Source=IT-DEV2\SQLEXPRESS;Initial Catalog=test;Integrated Security=True");
        string statment = string.Format("select item_code, Item_name, brand, size, section, price, Material, Qty, tax,tDate   from Items where tDate ='{0}'", TextBox2.Text);
        SqlDataAdapter da = new SqlDataAdapter(statment, con);
        DataSet ds = new DataSet();
        da.Fill(ds);
        DropDownList1.DataSource = ds.Tables[0];
        DropDownList1.DataTextField = "Item_name";
        DropDownList1.DataValueField = "item_code";
        DropDownList1.DataBind();
    }

<div>
<asp:TextBox ID="TextBox2" runat="server" ontextchanged="TextBox2_TextChanged"></asp:TextBox>
<asp:CalendarExtender ID="TextBox2_CalendarExtender" runat="server"
    Enabled="True" TargetControlID="TextBox2">
</asp:CalendarExtender>
<asp:DropDownList ID="DropDownList1" runat="server">
</asp:DropDownList>
</div>