Moving Forward

Trudging through object-oriented forest leads to some interesting results. The beauty of a strongly-typed language must also be it’s biggest downfall. In VB.NET in order to implement a polymorphic design pattern on a sensor class I had to learn the magic of DirectCasting an object. See the example below:

 
Public Class Form1
    Dim WithEvents oBaseClass As BaseClass
    Private Sub Form1_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
        oBaseClass = New ExtendedClass
        oBaseClass.Test() 'This doesn't work because the object was type casted.    
    End Sub
 
    Private Sub TestEventHdlr() Handles oBaseClass.TestEvent
        MsgBox("Event Fired")
    End Sub
End Class
 
Public Class BaseClass
    Public Event TestEvent()
End Class
 
Public Class ExtendedClass
    Inherits BaseClass
    Public Sub Test()
        MsgBox("Test")
    End Sub
End Class


Surprisingly this does not work!

The issue lies in direct-casting. In order to use extended functions inside an object one must direct cast it, like this:

Public Class Form1
Dim WithEvents oBaseClass As BaseClass 'Early bound'