ControlParameter可以'；找不到UserControl中的控件

我是ASP.NET的新手，但一直在努力，到目前为止，经过一点研究，我已经克服了所有的障碍。但我遇到了一个似乎无法解决的小问题，涉及到我创建的自定义控件。

该控件是一个通过JQuery弹出的小部件，包含允许用户对结果集进行筛选的控件。我把这个弹出窗口的所有元素都嵌入到了两个特定的页面中，这些页面都运行得很好。我决定创建一个自定义控件，据我所知，我在目标页面上使用了一个带有Control' directive and a Register指令的ascx文件，并且做得很正确，所以：

<%@ Control Language="C#" AutoEventWireup="true" CodeBehind="PopUp_TopicFilterControl.ascx.cs" Inherits="POD.PopUp_TopicFilterControl" %>

和

<%@ Register TagPrefix="popup" TagName="TopicFilterControl" Src="~/Controls/PopUp_TopicFilterControl.ascx" %>

"main"页包含一个对象数据源，它需要引用我的自定义控件中的控件以获取其选择参数。数据来源：

<asp:ObjectDataSource ID="TopicDataSource" runat="server" SelectMethod="GetRecentTopics" TypeName="POD.App_Objects.Topic">
    <SelectParameters>
        <asp:Parameter DefaultValue="12" Name="select_limit" Type="Int32" />
        <asp:ControlParameter DefaultValue="" ControlID="TopicCategoryFilterList" Name="category" Type="String" />
        <asp:ControlParameter DefaultValue="" ControlID="TopicCreatorFilterList" Name="creator" Type="Int32" />
        <asp:ControlParameter DefaultValue="" ControlID="TopicDateAfterFilterText" Name="date_after" Type="String" />
        <asp:ControlParameter DefaultValue="" ControlID="TopicDateBeforeFilterText" Name="date_before" Type="String" />
    </SelectParameters>
</asp:ObjectDataSource>

这是自定义控件的主体：

<asp:Panel id="TopicFilter_Panel" runat="server" CssClass="PopUp" ClientIDMode="Static" EnableTheming="False" EnableViewState="False" ViewStateMode="Disabled">
    <asp:Panel runat="server" CssClass="PopUp_Heading">
        <h1><a id="TopicFilter_Close" href="#">Close [X]</a></h1>
    </asp:Panel>
    <asp:Panel runat="server" CssClass="PopUp_Body">
        <asp:Table runat="server">
            <asp:TableRow runat="server">
                <asp:TableCell runat="server" HorizontalAlign="Right">
                    By Category:
                </asp:TableCell>
                <asp:TableCell runat="server">
                    <asp:DropDownList
                        ID="TopicCategoryFilterList"
                        runat="server"
                        DataSourceID="TopicCategoryDataSource"
                        DataTextField="value"
                        DataValueField="value"
                        AppendDataBoundItems="True"
                        AutoPostBack="False">
                        <asp:ListItem Selected="True" Value="">&mdash; All &mdash;</asp:ListItem>
                    </asp:DropDownList>
                </asp:TableCell>
            </asp:TableRow>
            <asp:TableRow runat="server">
                <asp:TableCell runat="server" HorizontalAlign="Right">
                    By Author:
                </asp:TableCell>
                <asp:TableCell runat="server">
                    <asp:DropDownList
                        ID="TopicCreatorFilterList"
                        runat="server"
                        DataSourceID="UserDataSource"
                        DataTextField="person_name_full"
                        DataValueField="user_id"
                        AppendDataBoundItems="True"
                        AutoPostBack="False">
                        <asp:ListItem Selected="True" Value="">&mdash; All &mdash;</asp:ListItem>
                    </asp:DropDownList>
                </asp:TableCell>
            </asp:TableRow>
            <asp:TableRow runat="server">
                <asp:TableCell runat="server" HorizontalAlign="Right">
                    By Date (After):
                </asp:TableCell>
                <asp:TableCell runat="server">
                    <asp:TextBox ID="TopicDateAfterFilterText" runat="server" />
                    <ajaxToolkit:CalendarExtender ID="TopicDateAfterCalendarExtender" TargetControlID="TopicDateAfterFilterText" PopupPosition="BottomRight" runat="server" />
                </asp:TableCell>
            </asp:TableRow>
            <asp:TableRow runat="server">
                <asp:TableCell runat="server" HorizontalAlign="Right">
                    By Date (Before):
                </asp:TableCell>
                <asp:TableCell runat="server">
                    <asp:TextBox ID="TopicDateBeforeFilterText" runat="server" />
                    <ajaxToolkit:CalendarExtender ID="TopicDateBeforeCalendarExtender" TargetControlID="TopicDateBeforeFilterText" PopupPosition="BottomRight" runat="server" />
                </asp:TableCell>
            </asp:TableRow>
            <asp:TableRow>
                <asp:TableCell ColumnSpan="2" VerticalAlign="Bottom" HorizontalAlign="Center">
                    <asp:Button runat="server" Text="Apply" CssClass="PopUp_Apply" />
                </asp:TableCell>
            </asp:TableRow>
        </asp:Table>
    </asp:Panel>
</asp:Panel>

我得到的错误只是对象数据源没有看到我的自定义控件中的控件（例如，"在ControlParameter"category"中找不到控件"TopicCategoryFilterList"）。显然这是一件非常简单的事情，但我似乎一辈子都无法简单地想办法让它发挥作用。我很确定这里一定已经解决了这个问题，但我找不到一个例子。

public partial class PopUp_TopicFilterControl : System.Web.UI.UserControl
{
    public string TopicCategory
    {
        get { return TopicCategoryFilterList.SelectedValue.ToString(); }
    }
}

<asp:ControlParameter
    DefaultValue=""
    ControlID="TopicFilterSelection"
    PropertyName="TopicCategory"
    Name="category"
    Type="String" />