is it possible to return an array of object Interface's rather than an object?

Question

I have an interface that describes an specialized list in my application...

Public Interface IAlphabeticListItem

    Property StartingLetter() As String
    Property DetailsList() As Generic.List(Of DetailsData)

End Interface

Multiple objects implement this interface, but I want to return them in a webservice not as the underlying object, but as the interface.

<WebMethod()> _
Public Function GetCategoryList(...) As Generic.List(Of IAlphabeticListItem)

    ...

End Function

Sadly, this causes an exception

Cannot serialize interface IAlphabeticListItem.

Exception Details: System.NotSupportedException: Cannot serialize interface IAlphabeticListItem.

Is there a way to make an interface serializable, or am I going to have to convert each of my objects into a concrete class implementing the interface, and then return that class?

Answer 1

Yes and no. You cannot directly expose the generic class for XML serialization because it's not supported. You can however expose a non-generic interface on the same collection and serialize that. This blog goes into great detail on how to make this work

http://srtsolutions.com/blogs/billwagner/archive/2006/11/20/xml-serialization-and-generic-interfaces.aspx

Answer 2

I don't have time to test it right now, but in C# you can extend interfaces, so I suppose you can do that in VB.NET.

Just make IAlphabeticListItem extend ISerializable