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WPF project and COM objects

Posted on 2015-01-12
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Hi Experts,

I have a WPF application that talks to a CLR class library that calls into C++.  The reverse is proving more difficult.  I've seen the method where you can pass a delegate as function pointer, but I find that too intrusive and need to change my C++ implementation to support it.

So I think my current best option might be to turn a class in my WPF application into a COM server.  I have done so, but since this is a WPF application, there is no dll output.  Clearly I could create another intermediate class library just for this COM object, and then use this class library from my WPF application.  But is there a way to use the exe instead of a dll to register in WIndows?

Also, if I do use an intermediate class library, how do I get this COM object to talk to the rest of the WPF application?  I can't instantiate it in my WPF program and have it CoCreated by the C++ native code that will be creating it as well....  

Thanks,
Mike
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Question by:thready
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jkr earned 500 total points
ID: 40545871
>> The reverse is proving more difficult.

Have you considered just passing windows messages to the WPF app by the C++ layer? Not sure if that is applicable, but you can pass a lot of stuff via the message parameters.
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by:thready
ID: 40545880
I did not think of that.  That's a much simpler idea!  I can keep this out of the cross platform c++ and inside of the class library as well...

I'm still curious about how one is supposed to CoCreate a class and have the class implementation talk to WPF...   It's created by the C++ side, so then it's in-process.  Does this mean that callbacks from the COM class will need to be static?  (I wonder if I'm not making sense here)....
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by:jkr
jkr earned 500 total points
ID: 40545886
You could still pass a C# delgate sink to the class in question upon construction or via an 'InitializeContext()' method after creating it - yet it is still a bit  to vague to say 'just do it'.
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Author Comment

by:thready
ID: 40545900
I don't really understand that method.  It makes sense to me, but how to do it with a .lib...  I don't know...  I'm starting to lose interest in trying to keep all business logic in c++ so that it's reusable everywhere.  Too time consuming- and what does it give me?  Not that much in the end.  I just wish my code base would never have to be touched again... But it seems I keep writing the same kinds of things for new projects.

If I do everything in C#, I'll be much better off.  Just no cross-platform stuff.  Please talk me out of dropping this if you think it's all worth it?  :-)
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Assisted Solution

by:jkr
jkr earned 500 total points
ID: 40545903
If you can do most of the stuff in C#, even the better - yet since you are still vague about your setup, it is hard to give any advice. If e,g, your underlying C++ lib&dll can take a target window handle that receives the messages I mentoined earlier, you could pass structs/classes via the 'lParam' parameter (either by custom messages or by utilizing WM_COPYDATA) that are close to give you the flexibility you might need.
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Author Closing Comment

by:thready
ID: 40545909
I have/had a goal to write all my business logic in pure cross-platform c++, with the idea that c++ was the most common denominator between systems with the best chance for reuse.  However, I don't have much code, but wanted to write everything one last time.  I think I'm not getting that much out of this goal though.  And I do like C# best.  I think in the name of completing projects fast with less headaches, I'll stick to C# for now....   and hopefully not kick myself later on..
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