asp.net 在DataList中取出隐藏域中的值

我在内容放入了一个DataList，在  <ItemTemplate>下是将绑定的一机构表，我想在ItemTemplate中放入一个隐藏域，并且把值通过层的方式传入下一个页面。现在的代码
 <asp:DataList ID="dlBrandsZhongXue" runat="server" RepeatColumns="8" RepeatDirection="horizontal"
                    OnItemDataBound="dlBrands_ItemDataBound">
                    <ItemTemplate>
                   
                        <div runat="server" id="mainDiv">
                            <table id="item" runat="server">
                                <tr>
                                    <td>
                                        <!--我想在页面.aspx.cs中取出值，或者直接将值保存放入下级页面，谁来看看 -->
                                     <asp:HiddenField ID="aa" runat="server" Value="why????出来" />                                      <a href="" >
                                      <asp:Image ID="img" runat="server" ImageUrl='<%# "~/image/"+Eval("BrandPic")%>' Height="61px"
                                            Width="103px" /></a>
                                    </td>
                                    <td>
                                        <!--层这里 -->
                                        <div id="divDetail" runat="server" style="display: none; width: 200px; height: 200px;
                                            background-color: #FFCC00; position: absolute; z-index: 1">
                                            <table id="Table1" runat="server" style="width: 200px; height: 200px;">
                                                <tr>
                                                    <td align="center">
                                                 
                                                        <span style="font-size: 13px; line-height: 20px">
                                                            <asp:HyperLink Text="机 构 概 览"  NavigateUrl="~/LinkCommon/BrandSurvey.aspx" ID="h1Brank" runat="server"></asp:HyperLink></span>
                                                    </td>
                                                </tr>
                                                <tr>
                                                    <td align="center">
                                                        <span style="font-size: 13px; line-height: 20px;">
                                                            <asp:HyperLink Text="评 论 留 言" NavigateUrl="#" ID="hlRe" runat="server"></asp:HyperLink></span></td>
                                                </tr>
                                                <tr>
                                                    <td align="center">
                                                        <span style="font-size: 13px; line-height: 20px;">
                                                            <asp:HyperLink runat="server" NavigateUrl="#" ID="hlDiscoutedPrice" Text="报 名 优 惠"></asp:HyperLink>
                                                        </span>
                                                    </td>
                                                </tr>
                                                <tr>
                                                    <td align="center">
                                                        <span style="font-size: 13px; line-height: 20px;">
                                                            <asp:HyperLink Text="网 站 链 接" NavigateUrl="#" ID="hlWeb" runat="server"></asp:HyperLink></span></td>
                                                </tr>
                                            </table>
                                        </div>
                                    </td>
                                </tr>
                            </table>
                        </div>
                    </ItemTemplate>
                </asp:DataList>