Question

I have created a singleton class to keep track of my data on my iPhone app. I know singleton’s only need to be instantiated once, but what is the best place to instantiate it? Should this be done in the appDelegate? I want to be able to call this singleton (which contains an NSMutableArray) from a multitude of classes so that I can have access to the array.

Here is my Class I wrote:

#import "WorkoutManager.h"

static WorkoutManager *workoutManagerInstance;

@implementation WorkoutManager
@synthesize workouts;

+(WorkoutManager*)sharedInstance {
    if(!workoutManagerInstance) {
        workoutManagerInstance = [[WorkoutManager alloc] init];
    }
    return workoutManagerInstance;
}

-(id)init {
    self = [super init];
    if (self) {
        workouts = [[NSMutableArray alloc] init];
    }
    return self;
}

@end

Answer 1

In almost all cases, the point of a singleton is you don’t care who first instantiates it. Whoever is the first to call [Something sharedSomething] will be the creator. You want to use the pattern given in ” How do I implement an Objective-C singleton that is compatible with ARC? ” It’ll ensure the singleton is created only one time.