CODEWITHSUNDEEP
vb.netinheritancepropertiesexpand
j__
j__

Reputation: 63

VB.NET - Extend property in child class

Maybe somebody can help me out please, i can imagine it is a common need: I have a base and a child class. The base class has a property named "hello". Now I need to add extended functionality in the property Set of the child - How can I achive that?

A code sample for further explanation:

Base Class:

Public MustInherit Class Base

    Private pHello as String = ""

    Public Property Hello As String
        Get
            Return pHello
        End Get
        Set(ByVal value As String)
                pHello = value
                'DoSomethingInBaseClass()
                MsgBox "BaseClass calling!" 'Just for testing
        End Set
    End Property

End Class

Child Class

Public Class Child
    Inherits Base

    Public Property Hello As String
        Get
            Return MyBase.Hello
        End Get
        Set(ByVal value As String)
                'DoSomethingInCHILDClass()
                MsgBox "ChildClass calling!" 'Just for testing
        End Set
    End Property

End Class

Property Set in Main

Public Class Main

    Public Sub DoIt()
        Dim InstChild as new Child
        InstChild.Hello = "test"
    End Sub

End Class

Basically what i want is, when setting the property, that I first get the Child MessageBox and then the Base MessageBox.

Sure I need to add a keyword in the Property definition(s). I played around with Shadows and Overrides, but either I get only the Child or only the Base Message.

Is there a way to get both?

Thank you very much!

Upvotes: 2

Views: 1507

Answers (2)

Vytas Bradunas
Vytas Bradunas

Reputation: 676

I recommend doing the work in an overridable function. This way you can have the child class do its work then call MyBase.overriddenFunction().

For example:

Base Class

Public MustInherit Class Base

    Private pHello as String = ""

    Public Property Hello As String
        Get
            Return pHello
        End Get
        Set(ByVal value As String)
                pHello = value
                doSomething()
                MsgBox "BaseClass calling!" 'Just for testing
        End Set
    End Property

    Private Overridable Sub doSomething()
        'Do base class stuff
    End Sub

End Class

Child Class

Public Class Child
    Inherits Base

    Public Property Hello As String
        Get
            Return MyBase.Hello
        End Get
        Set(ByVal value As String)
                doSomething()
                MsgBox "ChildClass calling!" 'Just for testing
        End Set
    End Property

    Private Overrides Sub doSomething()
        'Do child class stuff
        MyBase.doSomething()
    End Sub

End Class

Upvotes: 1

Gino
Gino

Reputation: 176

The problem is in the child class. Instead of returning myBase.hello just return Me.hello.
because at first me.hello of the child class will be equal to the hello of the base class. So when you override the property, at the base class it will remain the same, and it will only change on the child class.
so in order to get both of you should call: Base.Hello.get() and Child.Hello.get()

Upvotes: 0

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