关于GridView的FooterTemplate的有关问题

关于GridView的FooterTemplate的问题
下面是我的GridView控件的代码:我在Button单击事件里定了个gvDep.ShowFooter = true; 这句咋不管用啊?显示不出来。
<asp:GridView ID="gvDep" runat="server" AutoGenerateColumns="False" 
                        CellPadding="4" Font-Names="宋体" Font-Size="Medium" ForeColor="#333333" 
                        GridLines="None" Height="160px" Width="925px" 
                        onrowdeleting="gvDep_RowDeleting">
                        <AlternatingRowStyle BackColor="White" ForeColor="#284775" />
                        <Columns>
                            <asp:TemplateField HeaderText="部门编号">
                                <EditItemTemplate>
                                    <asp:Label ID="TxtDepID" runat="server" Text='<%# Bind("dep_id") %>'></asp:Label>
                                </EditItemTemplate>
                                <ItemTemplate>
                                    <asp:Label ID="LblDepID" runat="server" Text='<%# Bind("dep_id") %>'></asp:Label>
                                </ItemTemplate>
                                <HeaderStyle Width="80px" />
                                <FooterTemplate>
                                    <asp:Label ID="lblDepNewId" runat="server"></asp:Label>
                                </FooterTemplate>
                            </asp:TemplateField>
                            <asp:TemplateField HeaderText="部门名称">
                                <EditItemTemplate>
                                    <asp:TextBox ID="TxtDepName" runat="server" Text='<%# Bind("dep_name") %>'></asp:TextBox>
                                </EditItemTemplate>
                                <ItemTemplate>
                                    <asp:Label ID="LblDepName" runat="server" Text='<%# Bind("dep_name") %>'></asp:Label>
                                </ItemTemplate>
                                <FooterTemplate>
                                    <asp:TextBox ID="TxtNewDepName" runat="server"></asp:TextBox>
                                </FooterTemplate>
                            </asp:TemplateField>
                            <asp:TemplateField HeaderText="部门级别">
                                <EditItemTemplate>
                                    <asp:DropDownList ID="DdlDepGrade" runat="server" Text='<%# Bind("dep_grade") %>'></asp:DropDownList>
                                </EditItemTemplate>
                                <ItemTemplate>
                                    <asp:Label ID="LblDepGrade" runat="server" Text='<%# Bind("dep_grade") %>'></asp:Label>
                                </ItemTemplate>
                                <HeaderStyle Width="80px" />
                                <FooterTemplate>
                                    <asp:DropDownList ID="DdlNewDepGrade" runat="server"></asp:DropDownList>
                                </FooterTemplate>
                            </asp:TemplateField>
                            <asp:TemplateField HeaderText="部门类型">
                                <EditItemTemplate>
                                    <asp:DropDownList ID="DdlDepType" runat="server" Text='<%# Bind("dep_type") %>'></asp:DropDownList>
                                </EditItemTemplate>
                                <ItemTemplate>
                                    <asp:Label ID="LblDepType" runat="server" Text='<%# Bind("dep_type") %>'></asp:Label>
                                </ItemTemplate>
                                <HeaderStyle Width="80px" />
                                <FooterTemplate>
                                    <asp:DropDownList ID="DdlNewDepType" runat="server">
                                            <asp:ListItem Enabled="true" Text="0" Value="0"></asp:ListItem>
                                            <asp:ListItem Enabled="true" Text="1" Value="1"></asp:ListItem>
                                    </asp:DropDownList>
                                </FooterTemplate>
                            </asp:TemplateField>
                            <asp:TemplateField HeaderText="上级部门">
                                <EditItemTemplate>
                                    <asp:DropDownList ID="DdlDepHigher" runat="server" Text='<%# Bind("dep_higher") %>'></asp:DropDownList>
                                </EditItemTemplate>
                                <ItemTemplate>
                                    <asp:Label ID="LblDepHigher" runat="server" Text='<%# Bind("dep_higher") %>'></asp:Label>
                                </ItemTemplate>
                                <FooterTemplate>
                                    <asp:DropDownList ID="DdlNewDepHigher" runat="server"></asp:DropDownList>
                                </FooterTemplate>
                            </asp:TemplateField>
                            <asp:TemplateField HeaderText="操作">
                                <EditItemTemplate>
                                    <asp:LinkButton ID="LbtUpdate" runat="server" CausesValidation="True" 
                                        CommandName="Update" Text="更新"></asp:LinkButton>
                                    &nbsp;<asp:LinkButton ID="LbtCancel" runat="server" CausesValidation="False" 
                                        CommandName="Cancel" Text="取消"></asp:LinkButton>
                                </EditItemTemplate>
                                <FooterTemplate>
                                    <asp:LinkButton ID="LbtDepAdd" runat="server" Text="添加"></asp:LinkButton>
                                </FooterTemplate>
                                <ItemTemplate>
                                    <asp:LinkButton ID="LbtEdit" runat="server" CausesValidation="False" 
                                        CommandName="Edit" Text="编辑"></asp:LinkButton>
                                    &nbsp;<asp:LinkButton ID="LbtDelete" runat="server" CausesValidation="False" 
                                        CommandName="Delete" Text="删除"></asp:LinkButton>
                                </ItemTemplate>
                                <HeaderStyle Width="120px" />
                            </asp:TemplateField>
                            
                        </Columns>
                        <EditRowStyle BackColor="#999999" />
                        <FooterStyle BackColor="#5D7B9D" Font-Bold="True" ForeColor="White" 
                            BorderStyle="Solid" />
                        <HeaderStyle BackColor="#5D7B9D" Font-Bold="True" Font-Names="黑体" 
                            Font-Size="Large" ForeColor="White" HorizontalAlign="Center" 
                            VerticalAlign="Middle" />
                        <PagerStyle BackColor="#284775" ForeColor="White" HorizontalAlign="Center" />
                        <RowStyle BackColor="#F7F6F3" ForeColor="#333333" />
                        <SelectedRowStyle BackColor="#E2DED6" Font-Bold="True" ForeColor="#333333" />
                        <SortedAscendingCellStyle BackColor="#E9E7E2" />
                        <SortedAscendingHeaderStyle BackColor="#506C8C" />
                        <SortedDescendingCellStyle BackColor="#FFFDF8" />
                        <SortedDescendingHeaderStyle BackColor="#6F8DAE" />
                    </asp:GridView>

------解决思路----------------------
不是在Button事件指定,而是GridView内写好。
<asp:GridView ID="gvDep" runat="server"  ShowFooter = true...
------解决思路----------------------
有没用 Update panel  ?