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From: roozbeh on 10 Apr 2008 04:45
Hi,

i am not that good at c++ interfaces and classes,so...

Here is my situation:
for some apis windows wants me to give him a pointer to an interface.
(ie implement him an interface)
i have another dll that implements this interface and i can get it via
a function.
is it possible that i use that interface and reimplement one of its
functions and send back my new interface to windows?so i can benefit
from what has already implemented in that dll and also use my own?

I somehow managed to do this,but maybe because i dont know the proper
way when freeing interfaces i get errors.
(i simply call other interface functions in my interface)
For uknown reason the interface refcount i get for the first time from
dll is 6.
should i also call addref,queary and release of main interface when i
do it for myself?

thanks
From: SvenC on 10 Apr 2008 05:02
Hi roozbeh,

> Here is my situation:
> for some apis windows wants me to give him a pointer to an interface.
> (ie implement him an interface)
> i have another dll that implements this interface and i can get it via
> a function.
> ...
> I somehow managed to do this,but maybe because i dont know the proper
> way when freeing interfaces i get errors.
> (i simply call other interface functions in my interface)
> For uknown reason the interface refcount i get for the first time from
> dll is 6.
> should i also call addref,queary and release of main interface when i
> do it for myself?

Do not count on the return value of Addref/Release to assume when you
have to call AddRef/Release. Just follow the rules: when you create a
COM object you get an interface which is already addreffed for you, so
you must call Release once when you are finished. For any additional
QueryInterface or AddRef call you will need to call an additional Release.

So in your case: create the helper object which implements the interface
once in your object and when release it when your object is released.

If that dll is really giving you a special function to get an interface
pointer then you might get an interface pointer to an already created
object which is referenced by multiple users. So that might be the
reason why you get a ref count of 6.

More important: is anything not working as you expect?

--
SvenC
From: Alexander Nickolov on 11 Apr 2008 14:30
In COM this is called containment/delegation and it's certainly
possible. You implement all methods of the interface in question
on your object and for those you are not interested in you simply
delegate the calls to another object, while the ones you are interested
in you hanlde yourself and then possibly delegate if appropriate.

It begs the question, however, do you really need to delegate to
another object? For example for COM events it makes no sense -
simply do nothing for the events you don't care about (e.g. return
S_OK without any processing).

--
=====================================
Alexander Nickolov
Microsoft MVP [VC], MCSD
email: agnickolov(a)mvps.org
MVP VC FAQ: http://vcfaq.mvps.org
=====================================

"roozbeh" <roozbehid(a)gmail.com> wrote in message
news:0bb343e6-9717-455e-a667-a0e4306d4efd(a)2g2000hsn.googlegroups.com...
> Hi,
>
> i am not that good at c++ interfaces and classes,so...
>
> Here is my situation:
> for some apis windows wants me to give him a pointer to an interface.
> (ie implement him an interface)
> i have another dll that implements this interface and i can get it via
> a function.
> is it possible that i use that interface and reimplement one of its
> functions and send back my new interface to windows?so i can benefit
> from what has already implemented in that dll and also use my own?
>
> I somehow managed to do this,but maybe because i dont know the proper
> way when freeing interfaces i get errors.
> (i simply call other interface functions in my interface)
> For uknown reason the interface refcount i get for the first time from
> dll is 6.
> should i also call addref,queary and release of main interface when i
> do it for myself?
>
> thanks


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