Imports System.Console
Imports System.Windows.Forms
 
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 Dispo As Decimal)
        m_Kontonr = Kontonr
        m_Dispo = Dispo
        m_Kontostand = 2000
    End Sub
    Sub Buchung(ByVal Betrag As Decimal)
        If Betrag + Kontostand > m_Dispo Then
            m_Kontostand = Betrag + Kontostand
        Else
            Dim Abbrechen As Boolean = True
            RaiseEvent DispoGrenze(Me, Abbrechen)
            If Abbrechen = False Then
            End If
            m_Kontostand = Math.Max(m_Kontostand + Betrag, m_Dispo)
        End If
    End Sub
 
    Sub Ausgabe()
        Dim s As String = "Kontonr: " & Kontonr & ", " _
                          & "   Kontostand: " & Kontostand.ToString(".00") & _
                          "," _
                          & "   Disporahmen: " & Dispo
        WriteLine(s)
    End Sub
 
End Class
 
Class Test
    Shared WithEvents k As Konto
    Shared Sub Main()
        k = New Konto("123", -3000)
 
        With k
            .Ausgabe()
            WriteLine()
            .Buchung(-8000)
            .Ausgabe()
            WriteLine()
            .Buchung(-12000)
            .Ausgabe()
        End With
 
    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 - CType( _
            sender, Konto).Dispo & " 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