Is it bad form to synchronize NSUserDefaults in -(void)dealloc?

I load from NSUserDefaults in my object's init method. Can I save to NSUserDefaults in my object's dealloc method?

Something exactly like:

-(void)dealloc {
    NSUserDefaults *userDefaults = [NSUserDefaults standardUserDefaults];
    [userDefaults setObject:self.filenamesArray forKey:self.defaultsKey];
    [userDefaults synchronize];
    self.filenamesArray = nil;
    self.defaultsKey = nil开发者_开发问答;
    [super dealloc];
}

good, bad, ok? if it's not good, where would be better.

Edit:

Thanks for the detailed responses. All those things make sense. Another reason I discovered why this is a bad place to save to user defaults, is that dealloc is only called when an object deallocates nicely. If my app is killed, this code never runs. Similarly, if the app is pushed into the background (iOS 4) this doesn't run. I've also removed the explicit [userDefaults synchronize] call. It makes me a little nervous, but I put my trust in apple on this one. :)

It's bad because by the time -dealloc is called, other objects have given up interest in it. This can have lots of different implications.

The better place to set user defaults is the very moment a setting changes. That way it's persisted right away and the app can be killed with no worries about a setting not being persisted because parts of your object graph might already have gone away.

Synchronizing the user defaults in -dealloc is no different than anywhere else. This is because, crazy though it may seem, -dealloc is not in any way magical, and unlike, say, C++ destructors, -dealloc is actually exactly a typical method. You could be slightly more worried about passing self.filenamesArray to userDefualts, because thats actually something that may be held past the actual deallocation, but I trust that the user defaults retains it.

As to when you should [userDefaults synchronize];, people vary, and I personally disagree with @Joshua -- I never explicitly -synchronize, but rather let NSUserDefaults take care of it. Unless I am very much mistaken, it fires automatically when the app closes, as well as periodically otherwise. As it knows when it has been updated, and it needs to write the entire plist file at once, I think that I would rather let Apple's algos handle when its time to write the defaults, since it is takes non-trivial time (because it writes to the file system).

(Note that none of the last paragraph applies if you have special circumstances surrounding your user defaults, such as another application reading/writing them)