Can my singleton be improved?

Question

I am somewhat new to iOS 5 singletons and am using a singleton as documented here:

Something like this:

MyManager.h

#import <Foundation/Foundation.h>
@interface MyManager : NSObject

//Data for section 1
@property(nonatomic,copy) NSString * section1a;
@property(nonatomic, assign) NSUInteger section1b;


//Data for section 2
@property(nonatomic,copy) NSString * section2a;
@property(nonatomic, assign) NSUInteger section2b;

+ (id)sharedInstance;
@end

MyManager.m

@implementation MyManager
@synthesize section1a, section1b, section2a; , section2b;

+ (id)sharedInstance
{
    static dispatch_once_t pred = 0;
    __strong static id _sharedObject = nil;
    dispatch_once(&pred, ^{
        _sharedObject = [[self alloc] init]; // or some other init method
    });
    return _sharedObject;
}
@end

So I use it as follows:

MyManager * myManager = [MyManager sharedInstance];
myManager.data = self.data

Is this how you generally use the singleton? Am I missing anything? Sorry for the basic questions I just want to make sure I am doing it right.

Thanks

I'm not sure which differences do you mean in iOS 5 or other version. But I think you missing declare this in .m file: static MyManager *_sharedObject = nil; — Matrosov Oleksandr, Jul 19 '12 at 15:45
just for your sake, you would implement these two methods in your singleton class (besides the `+sharedInstance` method) `+allocWithZone:` and `+copyWithZone:`, and you can add a `static MyManager *_sharedObject;` member for your class as well. :) — holex, Jul 19 '12 at 15:51

score 1 · Answer 1 · edited May 23 '17 at 12:27

1

This is not a singleton because you can create multiple instances of this class with alloc/init methods. A right answer is here

edited May 23 '17 at 12:27

Community

1
1

answered Jul 19 '12 at 15:45

iSofTom

1,718
11
15

1

Well, this works, but a determined person will use the runtime methods like `class_createInstance` – Richard J. Ross III Jul 19 '12 at 15:49

score 1 · Accepted Answer · answered Jul 19 '12 at 15:55

1

You're doing it right. This is (currently :) the way to go and works fine with ARC enabled, multiple threads etc.

It isn't strictly a singleton, as you can alloc more instances of the class, but I don't think that's relevant in your case.

answered Jul 19 '12 at 15:55

Andreas Ley

9,109
1
47
57

can you help edit my code a bit so that it acts like a true singleton? – Strong Like Bull Jul 19 '12 at 16:34
I would actually advise against it, as there is almost never a reason to do so. The code you've posted works fine as it is. A "real" singleton would mean fiddling around with manual memory management - something that I'm glad I rarely have to do these days. :) – Andreas Ley Jul 19 '12 at 16:40

score 0 · Answer 3 · answered Jul 19 '12 at 15:46

0

I usually make my singleton as such (suppose we are making a singleton for Manager):

static (Manager *) instance;

+ (Manager *) getInstance
{
    if(!instance) instance = [[Manager alloc] init];
    return instance;
}

This is a very basic singleton (it doesn't take into account multithreading or other advanced features) but this is the basic format.

answered Jul 19 '12 at 15:46

Nosrettap

10,940
23
85
140

1

Bad idea, multithreaded code will make this fail faster than pulling the plug on your desktop. – Richard J. Ross III Jul 19 '12 at 15:47
I agree that multithreading code will make this fail; however, he never states that he wants a thread-safe singleton. I was just showing him the bare bones version – Nosrettap Jul 19 '12 at 15:49
@Nosrettap the whole point of a singleton is one instance. If multiple instances can be allocated, then this is not a singleton! – Richard J. Ross III Jul 19 '12 at 15:50
1

@RichardJ.RossIII If the program does not access this with multiple threads, then there will only be one instance. – Nosrettap Jul 19 '12 at 15:56

score 0 · Answer 4 · edited May 23 '17 at 11:55

0

Refer to this: Singleton in iOS 5? You should override allowWithZone to prevent rogue code from creating a new instance.

edited May 23 '17 at 11:55

Community

1
1

answered Jul 31 '12 at 19:53

Καrτhικ

3,833
2
29
42

Can my singleton be improved?

4 Answers4