Protected Overrides Sub OnColumnChanged _
        (e As System.Data.DataColumnChangeEventArgs)
 
        If e.Column.Unique Then
            'Abbruch, falls Wert in UNIQUE-Spalte vorhanden ist
            If Not IsProposedValueUnique(e) Then Exit Sub
        End If
 
        MyBase.OnColumnChanged(e)
 
        '.............
End Sub
 
Private Function IsProposedValueUnique _
        (ByVal e As DataColumnChangeEventArgs) As Boolean
 
        Dim found As Boolean = False
        Dim rowindex As Integer = -1
        Do
            rowindex += 1
            If e.Row IsNot Me.Rows(rowindex) Then
               found = _
               Me.Rows(rowindex)(e.Column.ColumnName).Equals(e.ProposedValue)
            End If
        Loop While Not found And rowindex < Me.Rows.Count - 1
        Return Not found
 
End Function