Question

I am creating an iPhone application, a game, and I am trying to understand and embrace the MVC architecture. I am planning to create a model, in this case called HighScoresModel that is responsible for holding all the information about high scores in my game.

1. Where should this model be created? In the AppDelegate? In the first view controller?
2. How should other view controllers access the model in order to pass messages like addScore:withDifficulty:?

Answer 1

I think the best option to to have a class method on HighScoresModel that will access a single, shared instance of the model from any object that needs it.

This is superior to the other options because no controller is responsible for instantiating the model, and the controllers are not unnecessarily coupled to the app delegate either.

As an example:

@interface HighScoresModel : NSObject

+ (HighScoresModel *)sharedHighScoresModel;
...

@end

@implementation HighScoresModel

static HighScoresModel *SharedHighScoresModel;

+ (HighScoresModel *)sharedHighScoresModel
{
    if (!SharedHighScoresModel)
    {
        SharedHighScoresModel = [[HighScoresModel alloc] init];
    }

    return SharedHighScoresModel;
}

...

@end

Hope this helps!