Cant fire dropDownList selection从后端更改事件

我无法在Selection更改时激发该方法。我正在从代码后面添加DropDownList本身。代码：

  private TableCell CreateMTPLTypeCell(int insurerId, string MTPLType)
        {
            TableCell rg = new TableCell();
            rg.ID = string.Concat("rg_", insurerId);
            rg.CssClass = "formItem";
            //if (insurerId == 14)
            //{
                DropDownList ddl = new DropDownList();
                ddl.ID = "MTPLTypes";
                ddl.Items.Add(new ListItem("Standard", "1")); // add list items
                ddl.Items.Add(new ListItem("DubultOCTA", "2"));
                ddl.Items.Add(new ListItem("DubultOCTA+vējst", "3"));
                //ddl.SelectedIndex =
                //    ddl.Items.IndexOf(ddl.Items.
                //        FindByValue(MTPLType));
                ddl.SelectedIndexChanged += new EventHandler(MTPLType_selectedIndexChange);
                ddl.AutoPostBack = true;
                rg.Controls.Add(ddl);
            //}
            return rg;
        }
        void MTPLType_selectedIndexChange(object sender, EventArgs e)
        {
            DropDownList ddl = (DropDownList)sender;
            int insurerId = Int32.Parse(ddl.ID.Replace("rg_", ""));
            MTPLQuotes quotes = proposal.Properties.MtplQuotes[insurerId];
            if (quotes == null) return;
            proposal.GetSingleMTPLQuote(insurerId, Helpers.PortalUtilities.CurrentUser, BrokerInfo.GetBrokerInfo().Country.ID);
            DrawMtplQuotes(mtplPaymentMappingsCount > 0);
        }

我是否遗漏了DropDownList对象上的一些额外参数？

有时它是这样工作的：在选择Change之后，它开始"加载"，但它没有到达方法。：/

在同一类中，我有一个带有onChange事件的表Cell(Text_Change(->这可以正常工作

private TableCell CreateInsurerMtplDiscountCell(int insurerId, decimal discount)
    {
        TableCell c = new TableCell();
        c.CssClass = "formItem";
        c.Style[HtmlTextWriterStyle.PaddingLeft] = "25px";
        TextBox txt = new TextBox();
        txt.ID = string.Format("ins_disc_{0}", insurerId);
        txt.Text = discount > 0 ? discount.ToString() : "";
        txt.TextChanged += new EventHandler(insurerDiscountPercent_TextChanged);
        txt.AutoPostBack = true;
        txt.Width = new Unit(40);
        c.Controls.Add(txt);
        Literal l = new Literal();
        l.Text = "%";
        c.Controls.Add(l);
        return c;
    }
    void insurerDiscountPercent_TextChanged(object sender, EventArgs e)
    {
        TextBox txt = (TextBox)sender;
        int insurerId = Int32.Parse(txt.ID.Replace("ins_disc_", ""));
        MTPLQuotes quotes = proposal.Properties.MtplQuotes[insurerId];
        if (quotes == null) return;
        decimal discountPercent;
        if (!Decimal.TryParse(txt.Text, out discountPercent))
            discountPercent = 0;
        quotes.InsurerDiscountPercent = discountPercent;
        foreach (MTPLQuote quote in quotes.Quotes)
            ApplyMtplInsurerDiscount(quote, discountPercent);
        DrawMtplQuotes(mtplPaymentMappingsCount > 0);
    }

修复了它-问题是关于TableCell.ID(rg.ID=string.Concat("rg_"，insurerId(；(。去掉它后一切都很好。有人知道为什么会这样吗？