CODEWITHSUNDEEP
c#vb.netinterfacecom-interop
Stefan Steiger
Stefan Steiger

Reputation: 82186

VB.net interface won't compile, why?

Question: I'm trying out to convert this here: http://support.microsoft.com/kb/828736 to VB.net

I got it to work in C#, and it should work without problems in VB.net, the only problem is the managed class won't compile, i get this error:
Error Class "ManagedClass" has to implement "Function Add(Number1 As Integer, Number2 As Integer) As Integer" for the ICalculator-Interface

Why? I see one function declared, and one implemented, and that with the same arguments... What's wrong ?

 Imports System
 Imports System.Collections.Generic
 Imports System.Text

Namespace TestLibrary2
' Interface declaration.
Public Interface ICalculator
    Function Add(ByVal Number1 As Integer, ByVal Number2 As Integer) As Integer
End Interface



' Interface implementation.
Public Class ManagedClass
    Implements ICalculator
    Public Function Add(ByVal Number1 As Integer, ByVal Number2 As Integer) As Integer
        Return Number1 + Number2
    End Function
End Class


End Namespace

Upvotes: 1

Views: 372

Answers (2)

Damien_The_Unbeliever
Damien_The_Unbeliever

Reputation: 239704

In VB.Net, you have to be explicit about your interface implementation - this allows more flexibility than C# (because you can name your functions whatever you like), but is a little more work.

Public Function Add(ByVal Number1 As Integer, ByVal Number2 As Integer) As Integer Implements ICalculator.Add
    Return Number1 + Number2
End Function

As both M.A. Hanin and myself have mentioned - it lets you pick the names, but neither of us mentioned yet why you might want to do this. One example would be if you're implementing two interfaces that both define the same method name. And you want to expose both of these methods as public methods on your class. In C#, you'd have to create at least one "wrapper" function that calls another to achieve this.

Upvotes: 5

rerun
rerun

Reputation: 25505

you just need to tell it that the class that has a function with exactly the same name and definition is really what you want to handle the interface function.

  Public Function Add(ByVal Number1 As Integer, ByVal Number2 As Integer) As Integer Implements ICalculator.Add
        Return Number1 + Number2
    End Function

Upvotes: 2

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