how to export datatable to xls file in vb.net

Imports Microsoft
Imports Microsoft.Office.Interop

''' <summary>
    ''' Write Excel file as given file name with given data.
    ''' </summary>
    ''' <param name="a_sFilename">full file name for create excel file.</param>
    ''' <param name="a_sData">data in dataset to be fill in excel shhet.</param>
    ''' <param name="a_sFileTitle">Title of Excel file.</param>
    ''' <param name="a_sErrorMessage">output parameter contains error message if error occurrs.</param>
    ''' <returns>bool</returns>
    Public Function ExportToExcel(ByVal a_sFilename As String, ByVal a_sData As DataSet, ByVal a_sFileTitle As String, ByRef a_sErrorMessage As String) As Boolean
        a_sErrorMessage = String.Empty
        Dim bRetVal As Boolean = False
        Dim dsDataSet As DataSet = Nothing
        Try
            dsDataSet = a_sData

            Dim xlObject As Excel.Application = Nothing
            Dim xlWB As Excel.Workbook = Nothing
            Dim xlSh As Excel.Worksheet = Nothing
            Dim rg As Excel.Range = Nothing
            Try
                xlObject = New Excel.Application()
                xlObject.AlertBeforeOverwriting = False
                xlObject.DisplayAlerts = False

                ''This Adds a new woorkbook, you could open the workbook from file also
                xlWB = xlObject.Workbooks.Add(Type.Missing)
                xlWB.SaveAs(a_sFilename, 56, Missing.Value, Missing.Value, Missing.Value, Missing.Value, _
                Excel.XlSaveAsAccessMode.xlNoChange, Missing.Value, Missing.Value, Missing.Value, Missing.Value)

                xlSh = DirectCast(xlObject.ActiveWorkbook.ActiveSheet, Excel.Worksheet)

                'Dim sUpperRange As String = "A1"
                'Dim sLastCol As String = "AQ"
                'Dim sLowerRange As String = sLastCol + (dsDataSet.Tables(0).Rows.Count + 1).ToString()

                For j = 0 To dsDataSet.Tables(0).Columns.Count - 1
                    xlSh.Cells(1, j + 1) = _
                        dsDataSet.Tables(0).Columns(j).ToString()
                    xlSh.Cells(1, j + 1).Font.Bold = True
                Next

                For i = 1 To dsDataSet.Tables(0).Rows.Count
                    For j = 0 To dsDataSet.Tables(0).Columns.Count - 1
                        xlSh.Cells(i + 1, j + 1) = _
                            dsDataSet.Tables(0).Rows(i - 1)(j).ToString()
                    Next
                Next
                xlSh.Columns.AutoFit()
                'rg = xlSh.Range(sUpperRange, sLowerRange)
                'rg.Value2 = GetData(dsDataSet.Tables(0))

                'xlSh.Range("A1", sLastCol & "1").Font.Bold = True
                'xlSh.Range("A1", sLastCol & "1").HorizontalAlignment = XlHAlign.xlHAlignCenter
                'xlSh.Range(sUpperRange, sLowerRange).EntireColumn.AutoFit()
               
                If String.IsNullOrEmpty(a_sFileTitle) Then
                    xlObject.Caption = "untitled"
                Else
                    xlObject.Caption = a_sFileTitle
                End If

                xlWB.Save()
                bRetVal = True
            Catch ex As System.Runtime.InteropServices.COMException
                If ex.ErrorCode = -2147221164 Then
                    a_sErrorMessage = "Error in export: Please install Microsoft Office (Excel) to use the Export to Excel feature."
                ElseIf ex.ErrorCode = -2146827284 Then
                    a_sErrorMessage = "Error in export: Excel allows only 65,536 maximum rows in a sheet."
                Else
                    a_sErrorMessage = (("Error in export: " & ex.Message) + Environment.NewLine & " Error: ") + ex.ErrorCode
                End If
            Catch ex As Exception
                a_sErrorMessage = "Error in export: " & ex.Message
            Finally
                Try
                    If xlWB IsNot Nothing Then
                        xlWB.Close(Nothing, Nothing, Nothing)
                    End If
                    xlObject.Workbooks.Close()
                    xlObject.Quit()
                    If rg IsNot Nothing Then
                        Marshal.ReleaseComObject(rg)
                    End If
                    If xlSh IsNot Nothing Then
                        Marshal.ReleaseComObject(xlSh)
                    End If
                    If xlWB IsNot Nothing Then
                        Marshal.ReleaseComObject(xlWB)
                    End If
                    If xlObject IsNot Nothing Then
                        Marshal.ReleaseComObject(xlObject)
                    End If

                Catch
                End Try
                xlSh = Nothing
                xlWB = Nothing
                xlObject = Nothing
                ' force final cleanup!
                GC.Collect()
                GC.WaitForPendingFinalizers()
            End Try
        Catch ex As Exception
            a_sErrorMessage = "Error in export: " & ex.Message
        End Try

        Return bRetVal
    End Function

Public Function GridExport(ByVal DGV As DataGridView) As Boolean
    If DGV.RowCount > 0 Then
        Dim filename As String = Application.StartupPath & "\Export_" + Format(Now, "hhmmss").ToString + ".xls"
        DGV.ClipboardCopyMode = DataGridViewClipboardCopyMode.EnableAlwaysIncludeHeaderText
        DGV.SelectAll()
        IO.File.WriteAllText(filename, DGV.GetClipboardContent().GetText.TrimEnd)
        DGV.ClearSelection()
        Process.Start(filename)
        Return True
    Else
        Return False
    End If
End Function