小弟我使用CascadingDropDown方式做了三个DropDownList, 怎么回绑数据

我使用CascadingDropDown方式做了三个DropDownList, 如何回绑数据?
即: 如做做一个界面aspx, 要同时实现对数据的新增和编缉都共用这个界面, 那么当编辑时, 我如何能使该dropDownList控件显示数据库中的值?
像一般的DorpDownList可以用DDl.Items.FindByValue(需要选值项).Selected = true;的方法做到, 但是用CascadingDropDown方式做的话,好像不行的..

HTML code

 HTS Code:<asp:DropDownList ID="ddl_HTS_Code" runat="server" CssClass="verdana10pt">                                            <asp:ListItem Text="-Select-" Value="-1"></asp:ListItem>                                        </asp:DropDownList>                                        &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;HTS                                        SubCode:<asp:DropDownList ID="ddl_HTS_SubCode" runat="server" CssClass="verdana10pt">                                            <asp:ListItem Text="-Select-" Value="-1"></asp:ListItem>                                        </asp:DropDownList>                                        &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;                                        HTS Name:<asp:DropDownList ID="ddl_HTS_Name" runat="server" CssClass="verdana10pt">                                            <asp:ListItem Text="-Select-" Value="-1"></asp:ListItem>                                        </asp:DropDownList>                                                                                <ajaxToolKit:CascadingDropDown ID="cdd_HTS_Code" runat="server" TargetControlID="ddl_HTS_Code"                                            Category="HTS_Code" PromptText="-Select-" LoadingText="[Loading data...]" ServicePath="HTS.asmx"                                            ServiceMethod="Get_HTS_Code">                                        </ajaxToolKit:CascadingDropDown>                                        <ajaxToolKit:CascadingDropDown ID="cdd_HTS_SubCode" runat="server" TargetControlID="ddl_HTS_SubCode"                                            Category="HTS_SubCode" PromptText="-Select-" LoadingText="[Loading data...]"                                            ServicePath="hTS.asmx" ServiceMethod="Get_HTS_SubCode" ParentControlID="ddl_HTS_Code">                                        </ajaxToolKit:CascadingDropDown>                                        <ajaxToolKit:CascadingDropDown ID="cdd_HTS_Name" runat="server" TargetControlID="ddl_HTS_Name"                                            Category="HTS_Name" PromptText="-Select-" LoadingText="[Loading data...]" ServicePath="HTS.asmx"                                            ServiceMethod="Get_HTS_Name" ParentControlID="ddl_HTS_SubCode">                                        </ajaxToolKit:CascadingDropDown>