验证控件的小问题

<EditItemTemplate>
                                                            <asp:TextBox ID="PhotoInfo" runat="server" Text='<%#Eval("ImgInfo") %>'></asp:TextBox>
                                                            <asp:RequiredFieldValidator ID="RequiredFieldValidator1" runat="server" ControlToValidate="PhotoInfo"
                                                                ValidationGroup="Group1">*</asp:RequiredFieldValidator>
                                                        </EditItemTemplate>
为空的时候为什么验证不了呢？
<asp:EditCommandColumn ButtonType="LinkButton" EditText="编辑" CancelText="取消" UpdateText="更新"
                                                        ValidationGroup="Group1"></asp:EditCommandColumn>