Lazy Instantiation in iOS

I had a bunch of code like this in the init for my first view controller. Paul Hegerty had mentioned lazy instantiation in his Stanford CS193 courses. And the boilerplate code in the AppDelegate for creating Managed Object Contexts and Persistent Store Coordinator uses it a log. So I understood the concept, but I hadn’t used it for my own globals. After listening to his most recent class, I decided to convert all of my init code to lazy instantiation.

One benefit of lazy instantiation is that you don’t allocate resources until you need to use the object. In my case, a better reason is that I’m not cluttering up my view controller with code that initializes global variables. In the Model, View, Controller design pattern, initialization code really doesn’t belong in the controller. But even more important, since I check for initialization in the class that creates the variable, I can’t forget to initialize the variable.

Old Code

    if (![Globals sharedInstance].showmePict ) {
        [Globals sharedInstance].showmePict = @"Either";
    }
    
    if (![Globals sharedInstance].targetSoundDelay ) {
        [[Globals sharedInstance] resetTargetDelay:TARGET_SOUND_DELAY];
    }
    

    if ( !([Globals sharedInstance].targetSound) ){
#ifdef SHOWME_TARGET_SOUND
        [[Globals sharedInstance] resetTargetSound:SHOWME_TARGET_SOUND];
#endif
    
#ifndef SHOWME_TARGET_SOUND
        [[Globals sharedInstance] resetTargetSound:@""];
#endif
    }

New Code

In the singleton for globals.

- (NSString *)showmePict {
    
    if (!_showmePict ) _showmePict = @"Either";
    return _showmePict;
}

- (NSUInteger)targetSoundDelay {
    
    if ( !_targetSoundDelay ) [self resetTargetDelay:TARGET_SOUND_DELAY];
    return _targetSoundDelay;
}

- (NSString *)targetSound {
    
    if ( !_targetSound ){
    #ifdef SHOWME_TARGET_SOUND
        [self resetTargetSound:SHOWME_TARGET_SOUND];
    #endif
        
    #ifndef SHOWME_TARGET_SOUND
        [self resetTargetSound:@""];
    #endif
    }
    return _targetSound;
}