export to excel "Non visible" gridview columns, VB basic in ASP.NET

Imports System
Imports System.Data
Imports System.Configuration
Imports System.IO
Imports System.Web
Imports System.Web.Security
Imports System.Web.UI
Imports System.Web.UI.WebControls
Imports System.Web.UI.WebControls.WebParts
Imports System.Web.UI.HtmlControls 
Public Class GridViewExport
    Public Shared Sub Export(ByVal fileName As String, ByVal gv As GridView)
        HttpContext.Current.Response.Clear()
        HttpContext.Current.Response.AddHeader("content-disposition", String.Format("attachment; filename={0}", fileName))
        HttpContext.Current.Response.ContentType = "application/ms-excel"
        Dim sw As StringWriter = New StringWriter
        Dim htw As HtmlTextWriter = New HtmlTextWriter(sw)
        '  Create a form to contain the grid
        Dim table As Table = New Table
        table.GridLines = gv.GridLines
        '  add the header row to the table
        If (Not (gv.HeaderRow) Is Nothing) Then
            GridViewExportUtil.PrepareControlForExport(gv.HeaderRow)
            table.Rows.Add(gv.HeaderRow)
        End If
        '  add each of the data rows to the table
        For Each row As GridViewRow In gv.Rows
            GridViewExportUtil.PrepareControlForExport(row)
            table.Rows.Add(row)
        Next
        '  add the footer row to the table
        If (Not (gv.FooterRow) Is Nothing) Then
            GridViewExportUtil.PrepareControlForExport(gv.FooterRow)
            table.Rows.Add(gv.FooterRow)
        End If
        '  render the table into the htmlwriter
        table.RenderControl(htw)
        '  render the htmlwriter into the response
        HttpContext.Current.Response.Write(sw.ToString)
        HttpContext.Current.Response.End()
    End Sub 
    ' Replace any of the contained controls with literals
    Private Shared Sub PrepareControlForExport(ByVal control As Control)
        Dim i As Integer = 0
        Do While (i < control.Controls.Count)
            Dim current As Control = control.Controls(i)
            If (TypeOf current Is LinkButton) Then
                control.Controls.Remove(current)
                control.Controls.AddAt(i, New LiteralControl(CType(current, LinkButton).Text))
            ElseIf (TypeOf current Is ImageButton) Then
                control.Controls.Remove(current)
                control.Controls.AddAt(i, New LiteralControl(CType(current, ImageButton).AlternateText))
            ElseIf (TypeOf current Is HyperLink) Then
                control.Controls.Remove(current)
                control.Controls.AddAt(i, New LiteralControl(CType(current, HyperLink).Text))
            ElseIf (TypeOf current Is DropDownList) Then
                control.Controls.Remove(current)
                control.Controls.AddAt(i, New LiteralControl(CType(current, DropDownList).SelectedItem.Text))
            ElseIf (TypeOf current Is CheckBox) Then
                control.Controls.Remove(current)
                control.Controls.AddAt(i, New LiteralControl(CType(current, CheckBox).Checked))
               
            End If
            If current.HasControls Then
                GridViewExportUtil.PrepareControlForExport(current)
            End If
            i = (i + 1)
        Loop
    End Sub
End Class
                                              

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Imports System
Imports System.Data
Imports System.Configuration
Imports System.IO
Imports System.Web
Imports System.Web.Security
Imports System.Web.UI
Imports System.Web.UI.WebControls
Imports System.Web.UI.WebControls.WebParts
Imports System.Web.UI.HtmlControls 
Public Class GridViewExportUtil
    Public Shared Sub Export(ByVal fileName As String, ByVal gv As GridView)
        HttpContext.Current.Response.Clear()
        HttpContext.Current.Response.AddHeader("content-disposition", String.Format("attachment; filename={0}", fileName))
        HttpContext.Current.Response.ContentType = "application/ms-excel"
        Dim sw As StringWriter = New StringWriter
        Dim htw As HtmlTextWriter = New HtmlTextWriter(sw)
        'Create a form to contain the grid'
        Dim table As Table = New Table
        table.GridLines = gv.GridLines
        '  add the header row to the table'
        If (Not (gv.HeaderRow) Is Nothing) Then
            GridViewExportUtil.PrepareControlForExport(gv.HeaderRow)
            table.Rows.Add(gv.HeaderRow)
        End If
        '  add each of the data rows to the table
        For Each row As GridViewRow In gv.Rows
            GridViewExportUtil.PrepareControlForExport(row)
            table.Rows.Add(row)
        Next
        '  add the footer row to the table'
        If (Not (gv.FooterRow) Is Nothing) Then
            GridViewExportUtil.PrepareControlForExport(gv.FooterRow)
            table.Rows.Add(gv.FooterRow)
        End If
        '  render the table into the htmlwriter'
        table.RenderControl(htw)
        '  render the htmlwriter into the response'
        HttpContext.Current.Response.Write(sw.ToString)
        HttpContext.Current.Response.End()
    End Sub 
    ' Replace any of the contained controls with literals'
    Private Shared Sub PrepareControlForExport(ByVal control As Control)
        Dim i As Integer = 0
        Do While (i < control.Controls.Count)
            Dim current As Control = control.Controls(i)
            If (TypeOf current Is LinkButton) Then
                control.Controls.Remove(current)
                control.Controls.AddAt(i, New LiteralControl(CType(current, LinkButton).Text))
            ElseIf (TypeOf current Is ImageButton) Then
                control.Controls.Remove(current)
                control.Controls.AddAt(i, New LiteralControl(CType(current, ImageButton).AlternateText))
            ElseIf (TypeOf current Is HyperLink) Then
                control.Controls.Remove(current)
                control.Controls.AddAt(i, New LiteralControl(CType(current, HyperLink).Text))
            ElseIf (TypeOf current Is DropDownList) Then
                control.Controls.Remove(current)
                control.Controls.AddAt(i, New LiteralControl(CType(current, DropDownList).SelectedItem.Text))
            ElseIf (TypeOf current Is CheckBox) Then
                control.Controls.Remove(current)
                control.Controls.AddAt(i, New LiteralControl(CType(current, CheckBox).Checked))
               
            End If
            If current.HasControls Then
                GridViewExportUtil.PrepareControlForExport(current)
            End If
            i = (i + 1)
        Loop
    End Sub
End Class

                                              

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