C++ Callbacks with objective-C, an application to RtMidi - objective-c

Question

I've read several of the previous discussion about the subject but since I'm relatively new to Objective-C, I don't really understand them. (Blocks, selectors, and delegate are very new to me).
Here is the situation:
I'm using those abstract class RtMidi that are written in c++
void MidiInApi :: setCallback( RtMidiIn::RtMidiCallback callback, void *userData )
{
if ( inputData_.usingCallback ) {
errorString_ = "MidiInApi::setCallback: a callback function is already set!";
RtMidi::error( RtError::WARNING, errorString_ );
return;
}
if ( !callback ) {
errorString_ = "RtMidiIn::setCallback: callback function value is invalid!";
RtMidi::error( RtError::WARNING, errorString_ );
return;
}
inputData_.userCallback = (void *) callback;
inputData_.userData = userData;
inputData_.usingCallback = true;
}
I also have a class that Reciever that implements that callback (rtMidiCallback).
And at some point in my main file I need to write something like this
midiIn->setCallback(rtMidiCallback);
This Would be in a c++ context but in Objective-C I have no idea how to do it.
If you have any ideas, pointers I would be glad to discuss about it with you. Thank you very much
Best,
greg.

Answer 1

It's possible to have C++ and Objective-C within the same project and even within the same file (Objective-C++ with file extension .mm). If the code you're using is designed for a C++ callback, it may be easier to provide that and communicate between different object types outside of that mechanism.
// CPPClass.h
#ifndef CPPClass_h
#define CPPClass_h
class CPPClass {
private:
id m_ocObject;
public:
CPPClass(id ocObject);
virtual ~CPPClass();
void verifyCPP();
};
#endif
// OCClass.h
#import <Foundation/Foundation.h>
class CPPClass;
#interface OCClass : NSObject {
CPPClass *cppObject;
}
- (void)ocCallback;
- (void)verifyOC;
#end
// OCClass.mm
#import "OCClass.h"
#import "CPPClass.h"
#include <iostream>
#implementation OCClass
- (id)init {
self = [super init];
if (self) {
cppObject = new CPPClass(self);
}
return self;
}
- (void)dealloc {
delete cppObject;
}
- (void)ocCallback {
NSLog(#"Objective-C called from C++");
}
- (void)verifyOC {
NSLog(#"Objective-C called from Objective-C");
cppObject->verifyCPP();
}
#end
CPPClass::CPPClass(id ocObject) : m_ocObject(ocObject)
{}
CPPClass::~CPPClass() {}
void CPPClass::verifyCPP() {
std::cout << "C++ called from Objective-C" << std::endl;
[m_ocObject ocCallback];
}
To activate this, some other .mm file would have:
#import "OCClass.h"
...
OCClass *test = [[OCClass alloc] init];
[test verifyOC];