Objective C - sample Singleton implementation

Question

*I definitely need a break... cause was simple - array was not allocated... Thanks for help. Because of that embarrassing mistake, I flagged my post in order to delete i

Answer 1

This is an error that can be avoided by some disziplined convention which is to always use curly brackets followed by if and else.

+(PeopleDatabase *)getInstance {
    @synchronized(self)
    {
        if (instance == nil)
            NSLog(@"initializing");
            instance = [[[self alloc] init] retain];
            NSLog(@"Address: %p", instance);
    }
    return(instance);
}

If instance is nil then the very next statement and only that is executed. And that is the nslog and not the allocation. Then instance is allocated anyway, regardless wether it was used before or not. This will provide you with a new singleton on each call. BTW that causes a leak.

+(PeopleDatabase *)getInstance {
    @synchronized(self)
    {
        if (instance == nil) {
            NSLog(@"initializing");
            instance = [[[self alloc] init] retain];
            NSLog(@"Address: %p", instance);
        }
    }
    return(instance);
}

But this error came in while debugging. It may confuse you but does not solve your original problem. Please add an alloc and init and retain for _arrayOfPeople as well.

-(id)init{
    if(self = [super init]) {
        Person* person = [[[Person alloc] initWithName:@"John" sname:@"Derovsky" descr:@"Some kind of description" iconName:@"johnphoto.png" title:Prof] retain];

        _arrayOfPeople = [[[NSMutableArray alloc] init] retain]; //dont forget the release
        [_arrayOfPeople addObject:person];
        NSLog(@"array count = %d", [_arrayOfPeople count]); // <== array count = 1 !!!  
        [person release];
    }
    return self;
}

In your code _arrayOfPeople is nil and addObject is sent to nil which does not cause an abort but does not do anything either. Then count is sent to nil wich returns 0/nil.