VB.Net Tutorial/Class Module/MustOverride

MustOverride method

<source lang="vbnet">Option Strict On

Imports System

MustInherit Public Class Control
   Public Sub New(top As Integer, left As Integer)
      Me.top = top
      Me.left = left
   End Sub
   Public MustOverride Sub DrawControl( )
   Protected top As Integer
   Protected left As Integer
End Class 
Public Class Label
   Inherits Control
   Public Sub New(top As Integer, left As Integer, contents As String)
      MyBase.New(top, left) 
      listBoxContents = contents
   End Sub
   Public Overrides Sub DrawControl( )
      Console.WriteLine("Writing string to the listbox: {0}", listBoxContents)
   End Sub 
   Private listBoxContents As String 
End Class
Public Class Button
   Inherits Control
   Public Sub New(top As Integer, left As Integer)
      MyBase.New(top, left)
   End Sub
   Public Overrides Sub DrawControl( )
      Console.WriteLine("Drawing a button at {0}, {1}" + ControlChars.Lf, top, left)
   End Sub 
End Class
Public Class Tester
   Shared Sub Main( )
      Dim winArray(3) As Control
      winArray(0) = New Label(1, 2, "A")
      winArray(1) = New Label(3, 4, "B")
      winArray(2) = New Button(5, 6)
      Dim i As Integer
      For i = 0 To 2
         winArray(i).DrawControl( )
      Next i
   End Sub "Main
End Class "Tester</source>

Writing string to the listbox: A
Writing string to the listbox: B
Drawing a button at 5, 6

MustOverrides MustInherit

<source lang="vbnet">public class MustOverrideMustInherit

  public Shared Sub Main
       Dim Emp1 As New Employee()
       Emp1.Name = "B"
       Console.WriteLine(GetName(Emp1))
       Dim Cus1 As New Customer()
       Cus1.Name = "T"
       Console.WriteLine(GetName(Cus1))
  End Sub
   Public Shared Function GetName(ByVal p As Person) As String
       Return p.Name
   End Function

End class Public MustInherit Class Person

   Public MustOverride Property Name() As String

End Class Public Class Employee

   Inherits Person
   Private m_Name
   Public Overrides Property Name() As String
       Get
           Return m_Name
       End Get
       Set(ByVal Value As String)
           m_Name = Value
       End Set
   End Property

End Class

Public Class Customer

   Inherits Person
   Private m_Name
   Public Overrides Property Name() As String
       Get
           Return m_Name
       End Get
       Set(ByVal Value As String)
           m_Name = Value
       End Set
   End Property

End Class</source>

B
T