Changing SaveFileDialog behaviour with filters - vb.net

Question

I have to export, under pressure of a button, some data in different extensions. To do this, I provided a SaveFileDialog, but depending on the filter (and so the output file extension), I have to write data with a different process:
if I have to export it as .txt or .csv, I have to use writer
otherwise if I have to export it as .xlsx, .xls or .ods I have to use NPOI
I provided the code both for writer and NPOI and they work singularly. If I try to put them together, .txt and .csv works, but for .xlsx, it exports a corrupted file.
This is the code I'm using:
Private Sub Button2_Click(sender As Object, e As EventArgs) Handles Button2.Click
SaveFileDialog1.Filter = "TXT Files (*.txt*)|*.txt|CSV Files (*.csv*)|*.csv|Excel 2010 Workbook (*.xlsx*)|*.xlsx|Excel 2000 Workbook (*.xls*)|*.xls|OpenOffice Spreadsheet (*.ods*)|*.ods"
SaveFileDialog1.CheckFileExists = False
Dim t As Integer
t = CInt(Form10.Label13.Text)
If SaveFileDialog1.ShowDialog() = DialogResult.OK Then
If SaveFileDialog1.Filter = "TXT Files (*.txt*)|*.txt|CSV Files (*.csv*)|*.csv|" Then
Using writer = New StreamWriter(SaveFileDialog1.FileName)
For Each o As Object In Form10.ListBox2.Items
writer.WriteLine(o)
Next
End Using
End If
End If
If SaveFileDialog1.Filter = "Excel 2010 Workbook (*.xlsx*)|*.xlsx|Excel 2000 Workbook (*.xls*)|*.xls|OpenOffice Spreadsheet (*.ods*)|*.ods|" Then
Dim fs As New FileStream(SaveFileDialog1.FileName, FileMode.Create, FileAccess.Write)
Dim workbook As IWorkbook = New XSSFWorkbook()
Dim worksheet As ISheet = workbook.CreateSheet()
Dim ich As ICreationHelper = workbook.GetCreationHelper()
Dim rows As New List(Of IRow)
Dim rowz As IRow = worksheet.CreateRow(0)
rowz.CreateCell(0).SetCellValue(ich.CreateRichTextString("Time [s]"))
rowz.CreateCell(1).SetCellValue(ich.CreateRichTextString("HRR [kW]"))
For i As Integer = 1 To t
Dim row As IRow = worksheet.CreateRow(i)
row.CreateCell(0).SetCellValue(CDbl(Form10.ListBox1.Items(i)))
row.CreateCell(1).SetCellValue(CDbl(Form10.ListBox2.Items(i)))
rows.Add(row)
Next i
workbook.Write(fs)
fs.Close()
End If
End If
End Sub
I'd like to know if the "if loop" is set properly for filters. Thanks all are gonna answer me. Best regards.

Answer 1

Just get the file path selected by the user and check its extension, e.g.
Select Case Path.GetExtension(SaveFileDialog1.FileName)
Case ".txt", ".csv"
'...
Case ".xlsx", ".xls", ".ods"
'...
End Select