如何把FormView里面的按钮设为UpdatePanle的Trigger

Question

RT 我希望Formview 里面的一个按钮能够触发 页面回传但是我这样写的时候                                        <asp:UpdatePanel ID="UpdatePanel1" runat="server">
                                            <ContentTemplate>
                                                <asp:FileUpload ID="FileUpload_photo" runat="server" EnableViewState="False" OnUnload="FileUpload_photo_Unload" />
                                                <asp:Button ID="btn_uploadphoto" runat="server" OnClick="btn_uploadphoto_Click" Text="上传" />
                                            </ContentTemplate>
                                            <Triggers>
                                                <asp:PostBackTrigger ControlID="btn_uploadphoto" />
                                            </Triggers>
                                        </asp:UpdatePanel>
运行时页面会提示我
A control with ID 'btn_uploadphoto' could not be found for the trigger in UpdatePanel 'UpdatePanel1'
前提：模板页--ManagerScript+UploadPanel
内容页加UpdatePanel 设置Trigger 目的是为了上传空间不会失效
.NET2.0