Class Konto
    Private m_Kontonr As String
    Private m_Kontostand As Decimal
    Private m_Dispo As Decimal
    Public Event DispoGrenze(ByVal sender As Object, ByRef Abbrechen As Boolean)
    ReadOnly Property Kontonr() As String
        Get
            Return m_Kontonr
        End Get
    End Property
    ReadOnly Property Kontostand() As Decimal
        Get
            Return m_Kontostand
        End Get
    End Property
    ReadOnly Property Dispo As Decimal
        Get
            Return m_Dispo
        End Get
    End Property
 
    Public Sub New(ByVal Kontonr As String, ByVal Kontostand As Decimal, ByVal _
      Dispo As Decimal)
        m_Kontonr = Kontonr
        m_Kontostand = Kontostand
        m_Dispo = Dispo
    End Sub
 
    Sub Buchung(ByVal Betrag As Decimal)
        If Betrag + m_Kontostand >= m_Dispo Then
            m_Kontostand = Betrag + Kontostand
        Else
            Dim Abbrechen As Boolean = True
            RaiseEvent DispoGrenze(Me, Abbrechen)
            If Abbrechen = False Then
                m_Kontostand = Betrag + Kontostand
            End If
        End If
    End Sub
 
    Sub Ausgabe()
        Dim s As String = _
            "Kontonr: " & Kontonr & ", Kontostand: " & Kontostand & "," & _
            "Disporahmen: " & Dispo
        WriteLine(s)
    End Sub
End Class
 
Class Test
    Shared WithEvents k As Konto
    Shared Sub Main()
        k = New Konto(123, 2000, -3000)
        k.Ausgabe()
        WriteLine()
        k.Buchung(-3000)
        k.Ausgabe()
        WriteLine()
        k.Buchung(-3000)
        k.Ausgabe()
    End Sub
 
    Private Shared Sub k_DispoGrenze(ByVal sender As Object, ByRef Abbrechen As _
      Boolean) Handles k.DispoGrenze
        Dim s As String = _
            "Der gewünschte Betrag kann nicht abgehoben werden," _
            & " da der Dispositionsrahmen überschritten wurde." _
            & vbCrLf & vbCrLf _
            & " Sie können noch " & CType(sender, Konto).Kontostand & "" & _
            "abheben." _
            & vbCrLf _
            & "Betrag abheben (Ja), Abbruch (Nein)."
 
        Dim Antwort As DialogResult
 
        Antwort = MessageBox.Show(s, "Buchung", MessageBoxButtons.YesNo, _
                                  MessageBoxIcon.Error, _
                                  MessageBoxDefaultButton.Button2)
 
        If Antwort = DialogResult.OK Then
            Abbrechen = False
        End If
 
    End Sub
End Class