Re: 'Pseudo' Singleton in Objective C
Re: 'Pseudo' Singleton in Objective C
- Subject: Re: 'Pseudo' Singleton in Objective C
- From: Jens Alfke <email@hidden>
- Date: Thu, 14 Mar 2013 11:38:26 -0700
On Mar 14, 2013, at 11:22 AM, Pax <email@hidden> wrote:
> My issue is that I only want one instance of the Information class to be loaded at a given time (and therefore only one information window on screen at a given time). If the information window is already loaded and it is then reselected from the menu then the existing window needs to be brought to the front - nothing more.
> I have currently resolved it by making my class a singleton - but that's not the right answer because it means that I can't release information window and its class when it gets closed, resulting in a minor leak (only minor because, as a singleton, the instance is only ever loaded once anyway).
IMHO the full belt-and-suspenders implementation of a singleton you’ve chosen — overriding alloc, retain, release, etc. — is overkill. I just implement singletons using a +sharedInstance method that looks like your +singleton. If I’m feeling paranoid I put an assertion into the -init method that the singleton doesn’t yet exist.
An easy way to make a sort of “weak singleton” like what you want, is to (a) make the static singleton pointer variable non-retained, and (b) nil it out in the -dealloc method. That way your singleton object isn’t kept around permanently, and when it goes away it cleans up so that the next request will instantiate a new one. (Of course you do have to ensure that *something* retains your singleton object as long as it needs to stay around, or else it’ll get dealloced very soon after being created and lose its state.
—Jens
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