Question

Callbacks from native C++ to CLI\C++

Asked by: adam_pedley

I have Native C++ code with a callback function of

typedef void (*InquiryCompleteCallback)(BOOL, short);

and a variable of

InquiryCompleteCallback            inquiryComplete;

Now from managed CLI\C++ code I can access this class by
Native::CSomeClass* someClass= new Native::CSomeClass;

Now how to I manage to get the call back into the manage code

I have been trying things like
someClass->inquiryComplete =  &ManagedClass::OnInquiryComplete;

but I get the error
error C3374: can't take address of 'ManagedClass::OnInquiryComplete' unless creating delegate instance

Could anyone please help.
Thanks

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Asked On
2007-10-29 at 05:56:59ID22924134
Tags

delegate

,

native

,

error

,

c

,

cli

Topics

C++ Programming Language

,

Microsoft Visual C++

Participating Experts
2
Points
500
Comments
4

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Answers

 

by: evilrixPosted on 2007-10-29 at 07:31:14ID: 20169672

 

by: evilrixPosted on 2007-10-29 at 07:42:17ID: 20169770

Follow the link to the example and read it -- it's pretty simple and well (sort of) explained!

 

by: itsmeandnobodyelsePosted on 2007-10-29 at 12:43:30ID: 20172629

In unmanaged C++ you can define a static function to use for a call back:

class Unmanaged
{
public:
     static void MyCallback(BOOL, short);
     
     ...
};

In managed C++ it is the __delegate specifier which makes a 'globally' defined function a valid callback function (see the link evilrix supplied).

In both cases you have the problem to call non-static or non-global functions from within the callback function. You normally do that by using one of the arguments that is passed to callback. If the callback was properly defined you can pass some kind of id when registeruing the callback function. That id was passed as an argument when the callback function was called. You then can retrieve the 'instance' of  a class (managed or unmanaged) by using that id, e. g. by calling a static 'retrieve' function where you pass the id.

class Managed
{
      static ManagedArray allobjects;    // holds all instances of Managed
      ...
public:
      ...
      static Managed& retrieve(int id)
      {
            return allobjects.get(id);
      }
};

I hope the above code will compile in a managed class (I have no experience with managed code). If not the concept should be valid nevertheless even if managed code requires a different syntax.

Regards, Alex

 

by: adam_pedleyPosted on 2007-10-30 at 00:05:47ID: 20175116

Thanks for your responses, I had already figured out the concept of callbacks it was the syntax that I couldn't get right, but I eventually figured it out.

someClass->inquiryComplete = &InquiryCompleteCallback(ManagedClass::OnInquiryComplete); //OnInquiryComplete;

and the OnInquiryComplete has to be static

I did a quick writeup of my solution at http://www.dotnetcore.com/tutorial.aspx?id=39 for anyone who stumbles upon this and wants to know more.

Thanks

20120131-EE-VQP-002

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