Public Sub AllesMarkieren(ByVal sender As Object, ByVal e As _
  System.Windows.Forms.KeyEventArgs)
 
    If e.Control Then
        Select Case e.KeyCode
            Case Keys.A
                sender.selectall()
        End Select
    End If
 
End Sub

AddHandler Textfeld1.KeyDown, AddressOf AllesMarkieren
AddHandler Textfeld2.KeyDown, AddressOf AllesMarkieren