VB.NET ComboBox selected item not remains effect than 2 times - vb.net

Question

I have a VB windows form application that has 02 ComboBox that provide newname input for a renaming file event. The first combobox provide prefix for new name comprise items (aa, bb, cc,... can add more through keydown button click event), the other combobox provide main name comprise items (XX, YY, ZZ,.. can also add more through keydown button click event). When I select "aa" from the first combobox, "XX" from the other then fire the rename event, the new file name should be "aa - XX", if file "aa - XX" has already existed then add "1" to the last as "aa - XX 1" and so on and if no item selected in prefix combobox the newname just be "XX" and increment. I get the old file name through a system openfiledialog. My code for rename as follows:
Private Sub Button2_Click(sender As Object, e As EventArgs) Handles Button2.Click
Dim var As String, prfix As String
var = ComboBox1.Text
prfix = ComboBox2.Text
If ComboBox2.Text = Nothing Then
If File.Exists(n & "\" & var & extn) = False Then
My.Computer.FileSystem.RenameFile(OpenFD.FileName, var & extn)
Else
Dim i As Integer = 1
Dim newfn As String = var & " " & i & extn
Dim m As String = n & "\" & newfn
While File.Exists(m)
newfn = var & " " & i & extn
m = n & "\" & newfn
i += 1
End While
My.Computer.FileSystem.RenameFile(OpenFD.FileName, newfn)
End If
Else
If File.Exists(n & "\" & prfix & " - " & var & extn) = False Then
My.Computer.FileSystem.RenameFile(OpenFD.FileName, prfix & " - " & var & extn)
Else
Dim j As Integer = 1
Dim newfn1 As String = prfix & " - " & var & " " & j & extn
Dim k As String = n & "\" & newfn1
While File.Exists(k)
newfn1 = var & " " & j & extn
k = n & "\" & newfn1
j += 1
End While
My.Computer.FileSystem.RenameFile(OpenFD.FileName, newfn1)
End If
End If
MessageBox.Show("Select a next file")
End Sub
My code run well 2 times. After I select "aa" and "XX" and leave it to rename, first result is "aa - XX", the second result is "aa - XX 1" but the third result is "XX", the forth is "XX 1" and then incrementing so on while the result should be "aa - XX 2" and next increment. I don't understand why combobox1 still effective but combobox2 as Nothing after no re-selecting the item in both comboboxes (2 times). I'm very new with VB so any advice should be much appreciated. Thanks.

Answer 1

In your lower Else block, you were incorrectly building up the file name.
You build up the first "newfn1" with:
Dim newfn1 As String = prfix & " - " & var & " " & j & extn
But then below, you used:
newfn1 = var & " " & j & extn
Notice the missing prefix and dash parts at the beginning.
Here's the full corrected version:
Dim j As Integer = 1
Dim newfn1 As String = prfix & " - " & var & " " & j & extn
Dim k As String = Path.Combine(n, newfn1)
While File.Exists(k)
j = j + 1
newfn1 = prfix & " - " & var & " " & j & extn
k = Path.Combine(n, newfn1)
End While
My.Computer.FileSystem.RenameFile(OpenFD.FileName, newfn1)

Answer 2

I'm a little confused by your explanation but if I understand correctly this should help,
Private Sub Button2_Click(sender As Object, e As EventArgs) Handles Button2.Click
CreateFile()
End Sub
Private BasePath As String = "" 'TODO
Private Ext As String = "txt"
Private Sub CreateFile()
If ComboBox1.SelectedIndex < 0 OrElse
ComboBox2.SelectedIndex < 0 OrElse
ComboBox1.SelectedItem.ToString = "" OrElse
ComboBox2.SelectedItem.ToString = "" Then
'error message
Exit Sub
End If
Dim fileName As String = String.Format("{0}-{1}.{2}",
ComboBox1.SelectedItem.ToString,
ComboBox2.SelectedItem.ToString,
Ext)
fileName = IO.Path.Combine(BasePath, fileName)
Dim ct As Integer = 1
Do While IO.File.Exists(fileName)
fileName = String.Format("{0}-{1}{3}.{2}",
ComboBox1.SelectedItem.ToString,
ComboBox2.SelectedItem.ToString,
Ext,
ct)
fileName = IO.Path.Combine(BasePath, fileName)
ct += 1
Loop
Dim fs As IO.FileStream = IO.File.Create(fileName)
fs.Close()
fs.Dispose()
End Sub