Objective C objects as instance variables in C++ classes

Question

I'm attempting to modify a C++ class in such a way that an Objective C object is one of its instance variables.

In essence, this question is like the reverse of this: C++ classes as instance variables of an Objective-C class

The header file MyCPPClass.h looks like this:

namespace my_namespace{

    class MyCPPClass: public my_namespace::OperationHandler {
     public:
         void someFunc();

     private:
         void otherFunc();
    };
}

And the MyCPPClass.mm file looks like this:

#include "MyCPPClass.h"
#import <Foundation/Foundation.h>

void my_namespace:: MyCPPClass:: someFunc() {
    NSLog(@"I can run ObjC here! Yahoo!");

    NSURLRequest *request = [NSURLRequest requestWithURL:[NSURL URLWithString:@"download_url_goes_here"]];
    NSURLSessionDataTask *task = [[NSURLSession sharedSession] dataTaskWithRequest:request completionHandler:^(NSData * _Nullable data, NSURLResponse * _Nullable response, NSError * _Nullable error) {
   // handle the data
   }];

}

void my_namespace:: MyCPPClass:: otherFunc() {
    NSLog(@"I can run ObjC here! Yahoo!");
}

The issue here is that I need to store a reference to an object created in someFunc() and then use it in otherFunc(). This object is an instance of NSURLSessionTask. My background in C++ is very limited :(. What is the least intrusive way to do this?

Community · Accepted Answer · 2017-05-23 11:44:15Z

1

I believe you can store it as a void*, according to this Pass an Objective-C object to a function as a void * pointer

So your header would become:

namespace my_namespace{

    class MyCPPClass: public my_namespace::OperationHandler {
        public:
            void someFunc();

        private:
            void otherFunc();
            void *mySessionTask;
    };
}

If you want to send a message to it you first cast it back to what it is supposed to be:

[(NSURLSessionTask*)mySessionTask someMessageWithArg: foo]

edited May 23, 2017 at 11:44

CommunityBot

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answered Jun 24, 2016 at 15:48

guysherman

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1 Comment

newacct Over a year ago

But then you lose the memory management of the variable which is based on the type.

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