Private Sub Text1_DblClick()
Dim GibtsSchon As Boolean
 
For N = 0 To List1.ListCount - 1
  If Trim(Text1.SelText) = Trim(List1.List(N)) Then
    GibtsSchon = True
    Exit For
  End If
Next
 
If GibtsSchon = False Then
  List1.AddItem Trim(Text1.SelText)
End If
End Sub