Abstract (MustInherit) Class

Imports System

Public Class MainClass
    
    Shared Sub Main()
       Dim winArray(3) As Window
       winArray(0) = New ListBox(1, 2, "First List Box")
       winArray(1) = New ListBox(3, 4, "Second List Box")
       winArray(2) = New Button(5, 6)

       Dim i As Integer
       For i = 0 To 2
          winArray(i).DrawWindow(  )
       Next i

    End Sub
End Class



 MustInherit Public Class Window

    Public Sub New(top As Integer, left As Integer)
       Me.top = top
       Me.left = left
    End Sub 'New

    Public MustOverride Sub DrawWindow(  )

    Protected top As Integer
    Protected left As Integer

 End Class 'Window

 Public Class ListBox
    Inherits Window

    Public Sub New(top As Integer, left As Integer, contents As String)
       MyBase.New(top, left) ' call base constructor

       listBoxContents = contents
    End Sub 'New


    Public Overrides Sub DrawWindow(  )
       Console.WriteLine("Writing string to the listbox: {0}", listBoxContents)
    End Sub 'DrawWindow

    Private listBoxContents As String 

 End Class 

 Public Class Button

    Inherits Window

    Public Sub New(top As Integer, left As Integer)
       MyBase.New(top, left)
    End Sub 

    Public Overrides Sub DrawWindow(  )
       Console.WriteLine("Drawing a button at {0}, {1}" + ControlChars.Lf, top, left)
    End Sub

 End Class

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Define Abstract Class and Reference Class by it

Abstract (MustInherit) Class : Abstract Class « Class « VB.Net

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