Export a GridView to Excel

Question

I'm trying to export a GridView into a xls file, I insert the GridView into a Modal and I'm supposing that because of that it can't be exported.

This is my BackEnd of the action from the Button :

protected void Btn_download_Click(object sender, EventArgs e)
        {
            Response.ClearContent();
            Response.AppendHeader("content-disposition", "attachment; flename=MainReport.xls");
            Response.ContentType = "application/excel";

            StringWriter stringWriter = new StringWriter();
            HtmlTextWriter htmlTextWriter = new HtmlTextWriter(stringWriter);

            Grv_main.RenderControl(htmlTextWriter);
            Response.Write(stringWriter.ToString());
            Response.End();
        }

and this is the HTML :

<form id="form1" runat="server">

        <div class="container">
            <div class="modal fade" id="History-Maint" role="dialog">
                <div class="modal-dialog modal-lg">
                    <div class="modal-content">
                        <div class="modal-header" style="padding: 35px 50px;">
                            <button type="button" class="close" data-dismiss="modal">&times;</button>
                            <h3><span class="glyphicon glyphicon-list-alt"></span>&nbsp Maintenance Report</h3>
                        </div>
                        <div class="modal-body">
                            <asp:GridView ID="Grv_main"
                                CssClass="table table-striped table-bordered table-hover"
                                runat="server"
                                AutoGenerateColumns="False"
                                Width="940px"
                                HorizontalAlign="Center"
                                DataKeyNames="id"
                                AllowPaging="True" OnRowEditing="GridView1_RowEditing">
                                <Columns>
                                    <asp:TemplateField HeaderText="id" Visible="false">
                                        <ItemTemplate>
                                            <asp:Label ID="Lbl_id" runat="server" Text='<%# Bind("id") %>'></asp:Label>
                                        </ItemTemplate>
                                        <ItemStyle HorizontalAlign="Center" />
                                    </asp:TemplateField>
                                    <asp:TemplateField HeaderText="status">
                                        <ItemTemplate>
                                            <asp:Label ID="Lbl_stats" runat="server" Text='<%# Bind("STATUS") %>'></asp:Label>
                                        </ItemTemplate>
                                        <HeaderStyle HorizontalAlign="Center" />
                                        <ItemStyle HorizontalAlign="Center" />
                                    </asp:TemplateField>
                                    <asp:TemplateField HeaderText="tool">
                                        <ItemTemplate>
                                            <asp:Label ID="Lbl_tool" runat="server" Text='<%# Bind("TOOL") %>'></asp:Label>
                                        </ItemTemplate>
                                        <HeaderStyle HorizontalAlign="Center" />
                                        <ItemStyle HorizontalAlign="Center" />
                                    </asp:TemplateField>
                                    <asp:TemplateField HeaderText="Area Change">
                                        <ItemTemplate>
                                            <asp:Label ID="Lbl_areach" runat="server" Text='<%# Bind("AREA") %>'></asp:Label>
                                        </ItemTemplate>
                                        <HeaderStyle HorizontalAlign="Center" />
                                        <ItemStyle HorizontalAlign="Center" />
                                    </asp:TemplateField>
                                    <asp:TemplateField HeaderText="responsable">
                                        <ItemTemplate>
                                            <asp:Label ID="Lbl_resp" runat="server" Text='<%# Bind("RESPONSABLE") %>'></asp:Label>
                                        </ItemTemplate>
                                        <HeaderStyle HorizontalAlign="Center" />
                                        <ItemStyle HorizontalAlign="Center" />
                                    </asp:TemplateField>
                                    <asp:TemplateField HeaderText="nota">
                                        <ItemTemplate>
                                            <asp:Label ID="Lbl_note" runat="server" Text='<%# Bind("NOTA") %>'></asp:Label>
                                        </ItemTemplate>
                                        <HeaderStyle HorizontalAlign="Center" />
                                        <ItemStyle HorizontalAlign="Center" />
                                    </asp:TemplateField>
                                    <asp:TemplateField HeaderText="fecha de modificacion">
                                        <ItemTemplate>
                                            <asp:Label ID="Lbl_mod" runat="server" Text='<%# Bind("MODIFY") %>'></asp:Label>
                                        </ItemTemplate>
                                        <HeaderStyle HorizontalAlign="Center" />
                                        <ItemStyle HorizontalAlign="Center" />
                                    </asp:TemplateField>
                                </Columns>
                            </asp:GridView>
                        </div>
                        <div class="modal-footer">
                            <asp:Button ID="Btn_download" runat="server" CssClass="btn btn-success" Text='Guardar' OnClick="Btn_download_Click" />
                        </div>
                    </div>
                </div>
            </div>
        </div>
        <asp:ContentPlaceHolder ID="ContentPlaceHolder2" runat="server">
        </asp:ContentPlaceHolder>
    </form>

all of this, is on a MasterPage and into a form with the runat="server"

Answer 1

The best for me has been to use ClosedXML

https://github.com/closedxml/closedxml

It's very easy and you can add sorting, and filtering built in.

Here's an example from the documentation:

var workbook = new XLWorkbook();
var worksheet = workbook.Worksheets.Add("Sample Sheet");
worksheet.Cell("A1").Value = "Hello World!";
workbook.SaveAs("HelloWorld.xlsx");

Answer 2

private void ExportGridToExcel()  {  
        Response.Clear();  

        //You had a typo on the line below in your code for (filename)

        Response.AddHeader("content-disposition", "attachment;filename=MainReport.xls");  
        Response.ContentType = "File/Data.xls";  
        StringWriter StringWriter = new System.IO.StringWriter();  
        HtmlTextWriter HtmlTextWriter = new HtmlTextWriter(StringWriter);  
        GridEmpData.RenderControl(HtmlTextWriter);  
        Response.Write(StringWriter.ToString());  
        Response.End();  
    }  

Made reference to this website http://www.c-sharpcorner.com/UploadFile/b926a6/gridview-data-export-into-excel-file-format/

Maybe take a look? There is databases there although the answer on how to convert a gridview to an Excel file is there and the code is above.