Export GridView to Excel Sheet in ASP.Net

Hi pdepirro,

I have modified your code please check.

HTML

<div>
    <asp:GridView ID="gvwTestMaint" runat="server" CssClass="table table-condensed table-bordered"
        AllowSorting="False" CellPadding="4" ForeColor="#333333" GridLines="None" AutoGenerateColumns="False"
        DataKeyNames="TDES_ID" HeaderStyle-HorizontalAlign="Center" AllowPaging="False">
        <AlternatingRowStyle BackColor="White" />
        <Columns>
            <asp:TemplateField>
                <ItemTemplate>
                    <asp:LinkButton ID="lnkBtn" runat="server" CommandArgument='<%# gvwTestMaint.Rows.Count.ToString() %>'
                        Text="Edit">Edit</asp:LinkButton>
                </ItemTemplate>
            </asp:TemplateField>
            <asp:BoundField DataField="TDES_ID" HeaderText="ID" SortExpression="TDES_ID" ItemStyle-Width="5%" />
            <asp:BoundField DataField="TDES_SYSTEM" HeaderText="System" ReadOnly="True" SortExpression="TDES_DESC"
                ItemStyle-Width="8%"></asp:BoundField>
            <asp:BoundField DataField="TDES_DESC" HeaderText="Description" ReadOnly="True" SortExpression="TDES_DESC"
                ItemStyle-Width="30%"></asp:BoundField>
            <asp:BoundField DataField="TDES_DETAIL" HeaderText="Detail" ReadOnly="True" SortExpression="TDES_DETAIL"
                ItemStyle-Width="40%"></asp:BoundField>
            <asp:BoundField DataField="TDES_CREATED_BY" HeaderText="Created By" ReadOnly="True"
                SortExpression="TDES_CREATED_BY"></asp:BoundField>
        </Columns>
        <EditRowStyle BackColor="#2461BF" />
        <FooterStyle BackColor="#507CD1" Font-Bold="True" ForeColor="White" />
        <HeaderStyle BackColor="#507CD1" Font-Bold="True" ForeColor="White" />
        <RowStyle BackColor="#EFF3FB" />
        <SelectedRowStyle BackColor="#D1DDF1" Font-Bold="True" ForeColor="#333333" />
        <SortedAscendingCellStyle BackColor="#F5F7FB" />
        <SortedAscendingHeaderStyle BackColor="#6D95E1" />
        <SortedDescendingCellStyle BackColor="#E9EBEF" />
        <SortedDescendingHeaderStyle BackColor="#4870BE" />
    </asp:GridView>
</div>
<asp:Button ID="btnExport" Text="ExportExcel" runat="server" OnClick="btnExport_Click" />
</form>

VB.NET

Protected Sub Page_Load(sender As Object, e As EventArgs)
    If Not IsPostBack Then
        Me.GetDataItem()
    End If
End Sub

Private Sub GetDataItem()
    Dim dt As New DataTable()
    dt.Columns.Add("TDES_ID", GetType(Integer))
    dt.Columns.Add("TDES_SYSTEM", GetType(String))
    dt.Columns.Add("TDES_DESC", GetType(String))
    dt.Columns.Add("TDES_DETAIL", GetType(String))
    dt.Columns.Add("TDES_CREATED_BY", GetType(DateTime))
    dt.Rows.Add(1, "TEST", "TEST", "TEST", DateTime.Now)
    dt.Rows.Add(2, "TEST", "TEST", "TEST", DateTime.Now)
    dt.Rows.Add(3, "TEST", "TEST", "TEST", DateTime.Now)
    dt.Rows.Add(4, "TEST", "TEST", "TEST", DateTime.Now)
    dt.Rows.Add(5, "TEST", "TEST", "TEST", DateTime.Now)
    gvwTestMaint.DataSource = dt
    gvwTestMaint.DataBind()
End Sub

Protected Sub btnExport_Click(sender As Object, e As EventArgs)
    Response.Clear()
    Response.Buffer = True
    Response.AddHeader("content-disposition", "attachment;filename=GridViewExport.xls")
    Response.Charset = ""
    Response.ContentType = "application/vnd.ms-excel"
    Using sw As New StringWriter()
        Dim hw As New HtmlTextWriter(sw)
        gvwTestMaint.AllowPaging = False
        Me.GetDataItem()
        gvwTestMaint.HeaderRow.BackColor = Color.White
        For Each cell As TableCell In gvwTestMaint.HeaderRow.Cells
            cell.BackColor = gvwTestMaint.HeaderStyle.BackColor
        Next
        For Each row As GridViewRow In gvwTestMaint.Rows
            row.BackColor = Color.White
            For Each cell As TableCell In row.Cells
                If row.RowIndex Mod 2 = 0 Then
                    cell.BackColor = gvwTestMaint.AlternatingRowStyle.BackColor
                Else
                    cell.BackColor = gvwTestMaint.RowStyle.BackColor
                End If
                cell.CssClass = "textmode"
            Next
        Next

        gvwTestMaint.RenderControl(hw)

        'style to format numbers to string
        Dim style As String = "<style> .textmode { } </style>"
        Response.Write(style)
        Response.Output.Write(sw.ToString())
        Response.Flush()
        Response.[End]()
    End Using
End Sub
Public Overrides Sub VerifyRenderingInServerForm(control As Control)
    ' Verifies that the control is rendered

End Sub

Screenshot

I hope works for you.