objective c - Release a singleton property - iphone

Question

I have a singleton class that has an mutableDictionary. I initialise the dictionary in my root viewController. later on I would like to empty the dictionary and release the memory. Even though the retain count is 1 the release causes a crash:
-[CFDictionary release]: message sent to deallocated instance
is it possible to release a singleton property?
Thanks

Answer 1

First I'll reiterate what has been said a ton of times on here: Don't call -retainCount!! It is an implementation detail.
See: StackOverflow | when to use retainCount for an excellent recount of why you don't use retainCount.
Beyond that, I'd recommend looking into more information about some of the invariants to shoot for in writing singletons. Dave DeLong has a great recap of how (and more importantly why he does singletons) a certain way. The article includes links to other developers and their outlooks. I'd recommend familiarizing yourself with those tenets and then re-evaluating you implementation.
Finally, just to say it one more time:
Please everyone go to http://bugreport.apple.com and request that -retainCount be deprecated. The more people that ask for it, the better.

Answer 2

You should not be releasing other objects' properties. Allow the singleton to manage the dictionary itself and your design will be simpler.
As for the problem where Cocoa says you're overreleasing even though "the retain count is 1", there is only one good piece of advice you'll ever get about retain counts:
Don't look at them!
They are deceptive and an object's actual memory management is affected by all sorts of forces that the retain count cannot tell you about.
In this case, you're checking the retain count to see if the object still exists. But there is no such thing as an object with a retain count of 0 — when you release an object with a retain count of 1, it's deallocated. Any result you get back from a deallocated object is garbage, so you'll never be able to ask an object for its retain count and get back 0 — objects with a retain count of 0 literally do not exist.

Answer 3

Any object that is allocated can be released later. Sounds like you're over-releasing. Check your properties and all references to the object to make sure you're not over-releasing it. If the dictionary is inside the singleton class, the singleton class should be in charge of releasing it, not the customer viewcontroller.

Answer 4

Agree with the comments re retainCount. Just don't do it.
Initialize the dictionary in the singleton
Add/remove objects from the dictionary as needed in other classes
The overhead of an empty dictionary is trivial, I wouldn't worry about releasing it when empty
Use [dictionary removeAllObjects] to remove everything when needed
If the dictionary is storing objects you want to release in the event of a memory warning, have the singleton observe UIApplicationDidReceiveMemoryWarningNotification and have it remove all it's objects there.
If you really want your implementation to release the entire dictionary I would override the synthesized getter and add singleton methods to interact with the dictionary as follows:
in MySingleton.m:
- (NSMutableDictionary *)myDictionary
{
if (!_myDictionary) {
_myDictionary = [[NSMutableDictionary alloc] init];
}
return _myDictionary;
}
- (void)setObject:(id)object inMyDictionaryForKey:(NSString *)key
{
[self.myDictionary setObject:object forKey:key];
}
- (void)removeObjectInMyDictionaryForKey:(NSString *)key
{
[self.myDictionary removeObjectForKey:key];
if ([self.myDictionary count] == 0) {
self.myDictionary = nil;
}
}
- (void)removeAllObjectsFromMyDictionary
{
self.myDictionary = nil;
}