Public Function GetFileMonthCounter(ByVal folder As String, _
     Optional ByVal Searchpattern As String = "*.*") As List(Of String)
 
   Dim FileMonthCounter As _
            New Collections.Generic.SortedDictionary(Of Date, Integer)
 
   With FileMonthCounter
 
      For Each fi As IO.FileInfo In _
         New IO.DirectoryInfo(folder).GetFiles(Searchpattern)
 
         'Das Erstellungsdatum auf den ersten Tag des Monats setzen
         Dim dt As New Date(fi.CreationTime.Year, fi.CreationTime.Month, 1)
         If .ContainsKey(dt) Then
            .Item(dt) += 1
         Else
            .Add(dt, 1)
         End If
      Next fi
 
   End With
 
   Dim fdc As New List(Of String), freq As String, dtf as string
 
   For Each item As KeyValuePair(Of Date, Integer) In FileMonthCounter
      dtf = Format(item.Key, "Y")
      freq = item.Value.ToString
      freq = New String(" "c, (4 - freq.Length) * 2) & freq
      fdc.Add(freq & " - " & dtf)
   Next item
 
   Return fdc
End Function