ASP.NET AJAX UpdatePanel下拉列表问题

Question

I have 2 drop-down lists (DDL), and below them an asp.net ajax updatepanel which I want to update/refresh based on selections in the 2 DDL. The second DDL's contents are dependent on what was selected in the first DDL.

The issue is that if I select something in the first DDL, it doesn't populate the second DDL, but without the ajax updatepanel it works perfectly. Please assist if possible. Below is the code. Thanks.

<asp:DropDownList runat="server" ID="ddlPrimary" AutoPostBack="true" OnSelectedIndexChanged="ddlPrimary_SelectedIndexChanged"></asp:DropDownList>
<asp:DropDownList runat="server" ID="ddlSecondary" AutoPostBack="true" OnSelectedIndexChanged="ddlSecondary_SelectedIndexChanged"></asp:DropDownList>

<asp:ScriptManager ID="sm" runat="server"></asp:ScriptManager>
<asp:UpdatePanel ID="up" runat="server">
    <ContentTemplate>
         <!-- asp.net repeater with table -->
         <tr>
              <td>
                  <asp:Label runat="server" ID="lblProdCode" Text='<%# Eval("ProdCode") %>'></asp:Label>
              </td>
              <td>
                  <asp:Label runat="server" ID="lblProdDesc" Text='<%# Eval("ProdDesc") %>'></asp:Label>
          </tr>
    </ContentTemplate>
    <Triggers>
                <asp:AsyncPostBackTrigger ControlID="ddlPrimary" EventName="SelectedIndexChanged" />
                <asp:AsyncPostBackTrigger ControlID="ddlSecondary" EventName="SelectedIndexChanged" />
     </Triggers>
 </asp:UpdatePanel> 

Answer 1

It will be ok if you move 2 DDL into UpdatePanel and remove trigger tag like this:

<asp:ScriptManager ID="sm" runat="server"></asp:ScriptManager>
<asp:UpdatePanel ID="up" runat="server">
<ContentTemplate>
     <!-- asp.net repeater with table -->
<asp:DropDownList runat="server" ID="ddlPrimary" AutoPostBack="true" OnSelectedIndexChanged="ddlPrimary_SelectedIndexChanged"></asp:DropDownList>
<asp:DropDownList runat="server" ID="ddlSecondary" AutoPostBack="true" OnSelectedIndexChanged="ddlSecondary_SelectedIndexChanged"></asp:DropDownList>

     <tr>
          <td>
              <asp:Label runat="server" ID="lblProdCode" Text='<%# Eval("ProdCode") %>'></asp:Label>
          </td>
          <td>
              <asp:Label runat="server" ID="lblProdDesc" Text='<%# Eval("ProdDesc") %>'></asp:Label>
      </tr>
</ContentTemplate>