Passing a Property to a function and setting the value to be retained

Question

I have two properties setup as ViewControllers that each use different NIB file. (Male and Female Models, will function the same but are setup visually different.) I want to have one function to create the ViewController based on the NIB Name and ViewController I pass in.

What's happening is the ViewController property is not being retained. If I add the actual property name within the function and set it, the viewController is set and retains the ViewController. Here is what I have in the .m file (Only showing what is needed to get help on.) I've kept in the two comment lines that I tried to do determine where the problem was.

@synthesize femaleModelViewController;
@synthesize maleModelViewController;


    - (void) loadModelViewControllerWithModelType:(NSString*) model ModelView:(ModelViewController *)modelViewController {
        ModelViewController *viewController = [[ModelViewController alloc] initWithNibName:model bundle:nil];
    //  [self setFemaleModelViewController:viewController];  // I don't want to set the property here, I want to be able to pass it as an argument.
        modelViewController = viewController;
    //  [modelViewController retain]; // I even tried to retain it do see if would but it doesn't.
        [viewController release];
    }

    - (void)viewDidLoad {
        [super viewDidLoad];
        [self loadModelViewControllerWithModelType:@"FemaleModel" ModelView:femaleModelViewController];
        [self loadModelViewControllerWithModelType:@"MaleModel" ModelView:maleModelViewController];


}

In the .h file my Properties are setup like so:

@property (nonatomic, retain) ModelViewController *femaleModelViewController;
@property (nonatomic, retain) ModelViewController *maleModelViewController;

Answer 1

Are you trying to assign a new ModelViewController to maleModelViewController and femaleModelViewController? If so, you're going about it the wrong way.

Frankly, I'd do away with the loadModelViewControllerWithModelType:modelView: method altogether. All you would need to do in viewDidLoad is this:

maleModelViewController = [[ModelViewController alloc] initWithNibName:@"MaleModel"];
femaleModelViewController = [[ModelViewController alloc] initWithNibName:@"FemaleModel"];

(This assumes that maleModelViewController and femaleModelViewController are the instance variables backing the properties of the same name.)

When you pass in maleModelViewController and femaleModelViewController, you're not passing a reference to those variables, you're passing their values. Since they haven't been initialized, all you're doing is passing in nil. To do what you're trying to do, you'd need to pass a pointer to the variables (i.e. declare the parameter as ModelViewController **, pass it in as &maleModelViewController and &femaleModelViewController and assign it using *modelViewController = viewController. If you're used to using pass-by-reference friendly languages like C# or Java, you should read up on how it works in C. (The rules are the same in Objective-C as in C).

HOWEVER, that is still complete overkill for what you're trying to do here.

Also, your code would still not work because you turn around and release viewController. This would cause it to be immediately deallocated, since the only reference you had to it came from when you alloced it. You would be assigning a dead reference that would crash your program as soon as you tried to use it.