Objective C ViewController with a C++ object as a property has getters and setters that re-initialise it every time it's referenced

Question

I have tried so many combination's of code I don't have a sample to show.

I have a Objective C view controller, and in the interface I declare a C++ class that contains the preferences of what the user wants to have. I do my @property command in the header and @synthesize command at the top of the .mm file.

Then I use the class in the loadView method and it initialises, which is a good thing and I load all the preferences into the class exactly how I want them to go, which is all fine.

Then down in the other methods such as numberOfSectionsInTableView and numberOfRowsInSection, etc, I go to use the class to retrieve the values, and this goes wrong.

The class initialises every time I go to use it. So when want to know how many groups in the preference file, the C++ method I called countGroup, it just reinitialises everything and there is no longer any data in my C++ class.

What I think, is that the @property command has generated the getters and setters in a way that specifically reinitialises classes. This is just a guess but if I'm right how do I over write them or is there some other way of using my C++ class globally through out my view controller.

Note: the C++ class doesn't work if it's referenced as a pointer because it's got loads of nested vectors and stuff, the compiler just throws a wobbly at that.

Answer 1

I had a similar story to you where I tried to use boost shared pointers and weird and crazy stuff kept happening.

Objective-C++ just doesn't work by the same rules as C++. The memory scope rules of C++ classes are not covered by Obj-C++. Things like smart pointers and vectors just won't work properly in Obj-C++.

The way that I got around it was to write a very simple container class:

class MyContainerClass
{
    public:
        boost::shared_ptr<MyClass> mySharedPointer;
        /// etc
};

Then in my Obj-C++ code I'd allocate/free the above the Obj-C++ way:

- (id)init
{
    if (self = [super init])
    {
        myContainer = new MyContainerClass();
        // etc
    }
    return self;
}

and

- (void)dealloc
{
    // etc
    delete myContainer;
    [super dealloc];
}

Then I'd have an accessor like:

- (boost::shared_ptr<MyClass>)mySharedPointer
{
    return myContainer->mySharedPointer;
}

It's an ugly approach but it's the only way I could figure out how to get around this issue.