我正在尝试在网格视图中插入模板字段。过程是在设计页面上单击网格视图元素〉编辑列〉添加模板字段〉确定。问题是模板字段既不能在代码的设计部分看到，也不能在源代码中看到。

<div class="row">
                            <asp:SqlDataSource ID="SqlDataSource1" runat="server" OnSelecting="SqlDataSource1_Selecting1" ConnectionString="<%$ ConnectionStrings:elibraryDBConnectionString %>" SelectCommand="SELECT * FROM [book_master_tbl]"></asp:SqlDataSource>
                            <div class="col">
                                <asp:GridView ID="GridView1" AlternatingRowStyle-CssClass="table table-striped table-bordered" runat="server" OnSelectedIndexChanged="GridView1_SelectedIndexChanged2" AutoGenerateColumns="False" DataKeyNames="book_id" DataSourceID="SqlDataSource1">
                                    <AlternatingRowStyle CssClass="table table-striped table-bordered"></AlternatingRowStyle>
                                    <Columns>
                                        <asp:BoundField DataField="book_id" HeaderText="book_id" ReadOnly="True" SortExpression="book_id"></asp:BoundField>
                                        
                                    </Columns>

                                </asp:GridView>
                            </div>
                        </div>