继承VB中的接口-从C＃移植代码

Question

So, I'm working with a library (Coderr, for anyone familiar with it), that's written in C#, and so are their examples. My project is of course in VB, and I'm a bit confused on implementing a template of their example classes.

An example of one of their existing classes is here .

I've attempted to port it by hand, and failed, so used Telerik's C# to VB converter. It outputs code that looks pretty good, and with only one tweak, the class itself works great. Except the inherits clause.

The code I've got it to now:

Namespace codeRR.Client.AspNet.CurrentUserContext    
    Public Class CurrentUserContext
        Inherits IContextInfoProvider

        Public Function Collect(ByVal context As IErrorReporterContext) As ContextCollectionDTO
            Dim CurrentUser As CurrentUser = CType(HttpContext.Current.Session("CurrentUser"), CurrentUser)
            If CurrentUser Is Nothing Then Return Nothing
            Dim converter = New ObjectToContextCollectionConverter()
            Dim collection = converter.Convert(Name, CurrentUser)
            Return If(collection.Properties.Count = 0, Nothing, collection)
        End Function

        Public ReadOnly Property Name As String
            Get
                Return "CurrentUser"
            End Get
        End Property
    End Class
End Namespace

So very similar to the example code, but returning my custom object instead, basically. The Inherits line fails with:

Classes can only inherit from other classes.

Which does make sense, since IContextInfoProvider is an Interface. I'm just stuck on how I actually use it in VB. I need to plug the class into a function that accepts an object of type IContextInfoProvider .

Answer 1

The error gives you a good indication of what the problem is. While a Class can inherit from another Class it can't inherit from an Interface.

Inheritance implies deriving some actual implementation of behaviour which a Class contains, as well as its 'signature' whereas an Interface simply defines its 'signature' with an expectation of the implementation of suitable behaviour in the implementing Class, hence it can only be implemented.

So,

Public Class CurrentUserContext
    Inherits IContextInfoProvider

should be

Public Class CurrentUserContext
    Implements IContextInfoProvider

Answer 2

Classes can inherit from other classes or they can implement interfaces. Interfaces traditionally start with an upper-case I , such as IContextInfoProvider .

In C#, a class can implement an interface or inherit from another class using the same syntax:

// Implement an interface
public class CurrentUserContext : IContextInfoProvider

// Inherit from a class
public class CurrentUserContext : MyContextBaseClass

In VB.Net, however, a class that implements an interface or a class that inherits from another class takes on two different syntax's:

' Implement an interface
Public Class CurrentUserContext
    Implements IContextInfoProvider

' Inherit from a class
Public Class CurrentUserContext
    Inherits MyContextBaseClass

In your case, you should be using Implements instead of Inherits since you are implementing an interface and not inheriting from a class.

I hope this clears things up!