iphone - Alternative to Singleton in Objective-C for better application design

Question

It seems a lot of Objective-C code is using Singleton nowadays.

While a lot of people complaining about Singleton, e.g. Google (Where Have All the Singletons Gone?), their fellow engineers also use it anyway: http://code.google.com/mobile/analytics/docs/iphone/

I know we had some answers in Stack Overflow already but they are not totally specific to Objective-C as a dynamic language: Objective C has categories, while many other languages do not.

So what is your opinion? Do you still use Singleton? If so, how do you make your app more testable?

Updated: I think we need to use codes as example for more concrete discussion, so much discussions on SO are theory based without a single line of code

Let's use the Google Analytics iOS SDK as an example:

// Initialization
[[GANTracker sharedTracker] startTrackerWithAccountID:@"UA-0000000-1"
                                        dispatchPeriod:kGANDispatchPeriodSec
                                              delegate:nil];
// Track page view
[[GANTracker sharedTracker] trackPageview:@"/app_entry_point"
                                   withError:&error];

The beauty of the above code is once you have initialized using the method "startTrackerWithAccountID", you can run method "trackPageview" throughout out your apps without passing through configurations.

If you think Singleton is bad, can you improve the above code?

Much thanked for your input, have a happy Friday.

Answer 1

This post is likely to be downvote-bait, but I don't really understand why singletons get no love. They're perfectly valid, you just have to understand what they're useful for.

In iOS development, you have one and only one instance of the application you currently are. You're only one application, right? You're not two or zero applications, are you? So the framework provides you with a UIApplication singleton through which to get at application-level os and framework features. It models something appropriately to have that be a singleton.

If you've got data fields of which there can and should be only one, and you need to get to them from all over the place in your app, there's totally nothing wrong with modeling that as a singleton too. Creating a singleton as a globals bucket is probably a misuse of the pattern, and I think that's probably what most people object to about them. But if you're modeling something that has "singleness" to it, a singleton might well be the way to go.

Some developers seem to have a fundamental disgust for singletons, but when actually asked why, they mumble something about globals and namespaces and aesthetics. Which I guess I can understand, if you've really resolved once and for all that Singletons are an anti-pattern and to be abhorred in all cases. But you're not thinking anymore, at that point. And the framework design disagrees with you.