Passing .NET references through COM objects

[David Vestal]

Suppose a COM object creates a .NET object (call it 'A') through a Com-
Callable Wrapper.

Can the COM object then pass a .NET reference to 'A' to a different .NET
object (call it 'B')? The goal is for 'B' to be able to use 'A' like any
other .NET object.


This is a much simpler way to ask the same question I was asking in my
recent post "Fairly complicated COM/.NET mixing."

 

[Mattias Sjögren]

David,

Can the COM object then pass a .NET reference to 'A' to a different .NET
object (call it 'B')? The goal is for 'B' to be able to use 'A' like any
other .NET object.

Yes



Mattias

 

[David Vestal]

David,


Yes

How?

 

[Mattias Sjögren]

David,

How?

Well it should "just work", no magic needed. I assume you are having
problems with it since you're asking. What's failing?



Mattias

 

[David Vestal]

David,


Well it should "just work", no magic needed. I assume you are having
problems with it since you're asking. What's failing?

It's more that I just don't know what variable type I should use in COM
code to represent a .NET reference.

Suppose my COM object instantiates a CCW-wrapped .NET object that exposes
as a property a System.Collections.Queue.

The COM object provides a getQueue method, which should return the property
exposed by the .NET object. What should the signature of this method be?

class COMObject : IUnknown{
public:
CComPtr<IDotNetObject> dotNetObject;

HRESULT getQueue([out, retval] ?Type? returnValue){
return dotNetObject->get_queueProperty(returnValue);
}
};

Obviously, the code is inexact, but what should I put in place of ?Type?
such that a .NET object could obtain the Queue exposed by IDotNetObject?

 

[Mattias Sjögren]

David,

Mscorlib.tlb contains interfaces for COM visible types in
Mscorlib.dll. If you #import it in your C++ code, you should be able
to use _Queue* as the parameter type.

That said, I personally wouldn't directly expose framework types like
that to COM, but instead write my own wrapper class so I could control
exactly which methods are visisble to the COM clients.



Mattias