VB.NET class inherits a base class and implements an interface issue (works in C#)

Question

I am trying to create a class in VB.NET which inherits a base abstract class and also implements an interface. The interface declares a string property called Description. T

Answer 1

This is a strange issue and it clearly shows a difference between the C# and VB.NET compilers. I would suggest that you do implement the interface on the abstract base class as this will make the VB.NET compiler happy and at execution time your child class will still have metadata indicating that it does in fact implement IFoo.

Is there a specific reason that the child class must be the one to declare that it implements the interface?

Answer 2

One way or the other, you must specify the implementation details of the IFoo interface.

What about this simple option?

Public Class MyFoo
    Inherits FooBase
    Implements IFoo
    Overloads Property Description() As String Implements IFoo.Description
        Get
            Return MyBase.Description
        End Get
        Set(ByVal value As String)
            MyBase.Description = value
        End Set
    End Property
End Class

Answer 3

VB requires that the implementing property declare the implementation. This is because of what I actually consider a nice feature of VB that I sometimes miss in C# -- that you can rename the member that implements the interface member.

Thus the only way to make this work without implementing IFoo.Description in FooBase is to declare Description Overridable and then define MyFoo as:

Public Class MyFoo
    Inherits FooBase
    Implements IFoo

    Public Overrides Property Description() As String Implements IFoo.Description
        Get
            Return MyBase.Description
        End Get
        Set(ByVal value As String)
            MyBase.Description = value
        End Set
    End Property
End Class

Answer 4

Sorry if I'm late to the party, and apologies too if this functionality has only been introduced in .NET 4, but the following is possible (now)

Public Interface IFoo
    Property Description() As String
End Interface

Public MustInherit Class FooBase
    Implements IFoo

    Public MustOverride Property Description As String Implements IFoo.Description
End Class

Public Class MyFoo
    Inherits FooBase

    Private _description As String

    Public Overrides Property Description As String
        Get
            Return _description
        End Get
        Set(value As String)
            _description = value
        End Set
    End Property
End Class

Answer 5

VB.NET does not support implicit implementation. I also ran into this issue and had a lot of trouble.

When you work with generated classes (entities etc.) where you have to explicitly declare Implements IFoo, it makes it impossible at all.

Therefore I submitted a connection to Microsoft and I hope you'll vote and next version of VB they will improve the compiler to be more clever.

Answer 6

I can't comment on M.A. Hanin's answer because of my rep, but I would recommend one small tweak to avoid compiler warnings about hiding base methods, assuming you don't want to or can't override override the property in the base class.

Public Class MyFoo
    Inherits FooBase
    Implements IFoo
    Private Property IFoo_Description() As String Implements IFoo.Description
        Get
            Return Me.Description
        End Get
        Set(ByVal value As String)
            Me.Description = value
        End Set
    End Property
End Class