为什么无法更新二级菜单中的下拉列表了,

今天用ajax做了下二级联动的菜单,照着别人做的,就是没法更新第二级中的数据,代码如下:

                <asp:DropDownList id="industry" runat="server" AutoPostBack="True" DataSourceID="ObjectDataSource2" DataTextField="Industry" DataValueField="IndustryId" OnSelectedIndexChanged="industry_SelectedIndexChanged">
                </asp:DropDownList>
                <asp:UpdatePanel id="UpdatePanel1" runat="server">
                    <contenttemplate>
                <asp:DropDownList ID="industryTwo" runat="server"
                    DataTextField="IndustryTwo" DataValueField="IndustryTowId">
                </asp:DropDownList>
</contenttemplate>
                    <triggers>
<asp:AsyncPostBackTrigger ControlID="industry" EventName="SelectedIndexChanged"></asp:AsyncPostBackTrigger>
</triggers>
                </asp:UpdatePanel>


industryTwo中的列表没法更新,实在是不知道错在哪,