Dim overzeichnis As String = "....."
 
Dim oextender As New List(Of String)
 
oextender.AddRange({"*.txt", "*.xls", "*.xlsx"})
oextender.Add("*.csv")
 
For Each oFile As String In My.Computer.FileSystem.GetFiles(
overzeichnis, FileIO.SearchOption.SearchAllSubDirectories, oextender.ToArray)
 
   'Stop
Next

Dim ox() As String = {}  'Array ohne Elemente
ox = ox.Append("*.txt").ToArray