We help IT Professionals succeed at work.

IUnkown as param

PastorDwayne asked
Last Modified: 2010-04-16

I need to pass IUnkown as a parameter to a function.  Here is how it is done in C++:

CComObject<CTestImpl> * m_pImpl;
ICallBackItf * pCallBk = 0;

What is the equivalent in C#?

Thanks for your time
Watch Question

You want to pass a callback to C# that calls into COM, is that it ?
You'll need COM interop.

In .NET you'll need the COM type definitions, and then it's just passing back a pointer and assigning it.

Have a look here:




Thanks for your response.  I followed the link, but wasn't able to find any pertinent info.  Here's more details:  I am attempting to access a COM object which has two interfaces.  I add a reference to my C# for this object; I am able to access one of the interfaces, and it's methods.  One of the method parameters is IUnknown of the second interface.  Here is what I thought might work:

CTestImpl m_spInterface1 = new CTestImpl ();
ICallBackItf cb = m_spInterface1  as ICallBackItf;

I thought I could query spInterface1 for the IUnknown of ICallBackItf, but it doesn’t work.
This one is on us!
(Get your first solution completely free - no credit card required)

Gain unlimited access to on-demand training courses with an Experts Exchange subscription.

Get Access
Why Experts Exchange?

Experts Exchange always has the answer, or at the least points me in the correct direction! It is like having another employee that is extremely experienced.

Jim Murphy
Programmer at Smart IT Solutions

When asked, what has been your best career decision?

Deciding to stick with EE.

Mohamed Asif
Technical Department Head

Being involved with EE helped me to grow personally and professionally.

Carl Webster
CTP, Sr Infrastructure Consultant
Empower Your Career
Did You Know?

We've partnered with two important charities to provide clean water and computer science education to those who need it most. READ MORE

Ask ANY Question

Connect with Certified Experts to gain insight and support on specific technology challenges including:

  • Troubleshooting
  • Research
  • Professional Opinions
Unlock the solution to this question.
Join our community and discover your potential

Experts Exchange is the only place where you can interact directly with leading experts in the technology field. Become a member today and access the collective knowledge of thousands of technology experts.

*This site is protected by reCAPTCHA and the Google Privacy Policy and Terms of Service apply.


Please enter a first name

Please enter a last name

8+ characters (letters, numbers, and a symbol)

By clicking, you agree to the Terms of Use and Privacy Policy.