C# exposing class to COM - Generic Collections

Question

We have a small framework written in C# .Net 2.0 that we want to expose to COM.

Problem is, we have some generic classes that would be exposed as the following:

interface IOurClass
{
  ReadonlyCollection<IOurListObject> OurCollection
  {
    get;
  }
}

interface IOurListObject
{
  //Some properties that don't matter
}

What is the best (or recommended way) to expose generic collections to COM? We do not have to support generics, we just need to somehow expose a collection of IOurListObject.

We also would like to avoid having to write a new class for every collection we use, but it may not be possible.

Answer 1

It is not possible to expose generic collections (or any other thing that is 'generic') to COM.

So, I suggest that you create a non-generic property (or method) in your COM-visible interface. This method could return an array of 'IOurListObject' items. In your class, you could implement this method explicitly, so that it does not show up in your intellisense when you refer to the object directly outside COM, for instance.

I hope I make myself a bit clear.

Example:

[ComVisible(true)]
public interface IOurClass
{
    IOurListObject[] OurCollection { get; }
}

public class OurClass : IOurClass
{
    IOurListObject[] IOurClass.OurCollection { get { return OurCollection.ToArray();} }

    public ReadOnlyCollection<IOurListObject> OurCollection { ... }
}

Answer 2

Check out this post. Either use a straight forward array or use an ArrayList. Seems like a step backwards, but generic collections don't play nice with COM.