CODEWITHSUNDEEP
objective-ccocoadesign-patterns
janeh
janeh

Reputation: 3804

Application design - Who should own a singleton object

In my document-based application, I have an AppController that deals with opening Prefs, the About panel, etc. I also have a singleton class; since it's basically a global object that gets passed around, who should own it? An object that uses it or my AppController? Some articles I read say that you should have one "central" place - like a Delegate, others say that it's bad design, and that only an object that uses class X should own class X. What's your take?

Upvotes: 0

Views: 113

Answers (3)

kothvandir
kothvandir

Reputation: 2161

You shouldn't use a singleton as a way to define a global object, the singleton pattern is intented to provide a way to assure an unique instance in one context. But the problem is that if you don't use a dependency injection framework and implement it through java, the static method used to implement the pattern lets all application classes access freely to the singlenton. So its a way to start destroying your own module/application design (if you don't control it correctly).

Take a look at this posts before you decide to use or not the singleton pattern (both against and pro):

Upvotes: -1

Whit
Whit

Reputation: 31

Nothing really owns the singleton because it is stored in a static variable like this:

static Globals *sharedGlobals = nil;

@implementation Globals

+ (Globals *) sharedGlobals {
    if (!sharedGlobals) sharedGlobals = [[Globals alloc] init];
    return sharedGlobals;
}

The first time the sharedGlobals method gets called, the singleton will be created by whichever class called it. It doesn't really matter who calls it first.

Upvotes: 2

Mil0R3
Mil0R3

Reputation: 3956

I think the singleton object is just existed in memory after alloced first time, it should not be owned by any object.

Upvotes: 0

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