Calling Objective-C method from C++ method? [2] - c++

Question

i found a great post Calling Objective-C method from C++ method?
however, i have to 2 questions, which makes me overcoming this issue very problematic :
note that i have made a change to MyObject-C-Interface.h
#ifndef __MYOBJECT_C_INTERFACE_H__
#define __MYOBJECT_C_INTERFACE_H__ 1
struct CWrap {
void * myObjectInstance;
int MyObjectDoSomethingWith (void *parameter) {
//how to call the
//myObjectInstance->MyObjectDoSomethingWith ???
}
}
#endif
1) how can i call a method on a void * myObjectInstance…
i mean, i cannot cast to MyObject or otherwise let the compiler know, what method to call:(
2) how do i actually use it?
in my, lets say code.m that has both the
#import "MyObject.h"
//and
#include "MyObject-C-Interface.h"
i would do?
MyObject tmp = [[MyObject alloc] init];
CWrap _cWrap;
_cWrap.myObjectInstance = (void *)tmp;
//pass the CWrap to a deep C++ nest
myMainCPPCode->addObjectiveCToCWrap(_cWrap);
and than in my deep C++ code simply call
_cWrap.MyObjectDoSomethingWith((void *)somePrameter)
iam missing a link, and thats, how to link the C wraper function to a ObjectiveC function :(
thank you

Answer 1

i mean, i cannot cast to MyObject or otherwise let the compiler know, what method to call
Why not?
Your C++ wrapper class must be in an Objective-C++ file (usually denoted with the .mm) extension. Then, because you even have to declare your private instance variables in the class declaration, you need a private member to hold the Objective-C pointer in the class header. This must be something that a pure C++ compiler can understand so one thing you could do is this:
#ifndef __MYOBJECT_C_INTERFACE_H__
#define __MYOBJECT_C_INTERFACE_H__ 1
#if defined __OBJC__
typedef id MyObjCClass;
#else
typedef void* MyObjCClass;
#endif
struct CWrap {
MyObjCClass myObjectInstance;
int MyObjectDoSomethingWith (void *parameter);
}
Then in the .mm file
#import "ObjCClassHeader.h"
int CWrap::MyObjectDoSomethingWith(void *parameter)
{
return [myObjectInstance doSomethingWith: parameter];
}
__OBJC__ is a predefined macro that is defined when the compiler is compiling Objective-C or Objective-C++