VB.net 抓取不重複的副檔名

Dim DirInfo As IO.DirectoryInfo
DirInfo = New IO.DirectoryInfo("D:\test")
  For Each file In DirInfo.GetFiles("*.*", IO.SearchOption.TopDirectoryOnly)
'設定抓檔案(*.jpg)限定在此資料夾下不包含子資料夾  
    If ListBox1.Items.Contains(Microsoft.VisualBasic.Right(file.Name, Len(file.Name) - InStr(1, file.Name, "."))) = False Then
       ListBox1.Items.Add(Microsoft.VisualBasic.Right(file.Name, Len(file.Name) - InStr(1, file.Name, ".")))
    End If
  Next file