My base class has properties that are used by a subclass. where should Release be called? In the original base class or the class that inherits it?
A:
I'm pretty new to Objective-C, so I'm also curious what the best answer is here. I would think that you should set the property to nil in the parent class -dealloc, where the property is synthesized. If you're retaining it in the subclass for some reason, you should also release it in the subclass, but setting the property to nil in the superclass shouldn't have any negative side effects.
pix0r
2009-06-23 05:43:50
Apple documents that you should not use property setters in init/dealloc, so you should not be setting the property to nil, but simply calling [ivar release]. If you also need to set the ivar to nil, then you are doing something wrong which should be corrected (eg removing timers/observations/deffered method calls).
Peter N Lewis
2009-06-23 07:42:36
Good to know, thanks.
pix0r
2009-06-23 21:55:15
+4
A:
I would say that each class manages it's own properties. So subclass class should release it's properties and base class releases it's own.
Once subclass is released it will not access base class properties, it technically does not exists anymore. Standard way of writing dealloc is:
- (void)dealloc
{
// release my stuff, after this line
// I don't exist and do not need to access any of my properties
[super dealloc];
}
stefanB
2009-06-23 05:51:59
Agreed. This is always my rule in OO programming, regardless of the language. Properties are ownership-based like Objective-C memory management — the two are almost always one and the same, since properties are essentially a nice way of accessing instance variables. Always release ivars in the class that declares them, never in any of its subclasses (if it has any). It's essentially the same pattern of matching retain and release calls.
Quinn Taylor
2009-06-23 08:12:19
+2
A:
If the properties are only used by the subclass, they should be defined in the subclass (not the parent class) and the subclass should release them within it's -(void)dealloc function. You'd have something like this:
- (void)dealloc
{
[username release];
[password release];
[super dealloc];
}
Note that we don't call dealloc on the properties! We just call "release" which signifies that we no longer will be using them and the system can clean them up (providing nobody else is using them).
Ben Gotow
2009-06-23 05:52:28
A:
In a given block, the number of calls to retain, copy, alloc should be balanced by calls to release, autorelease. If you retain something in the subclass, release it in the subclass, and if in the base class...
I'm paraphrasing that from memory from an article on stepwise.
Walker Argendeli
2009-06-23 06:11:43
Never paraphrase the memory mangement rules. Simply reference them directly: <http://developer.apple.com/documentation/Cocoa/Conceptual/MemoryMgmt/Articles/mmRules.html>. The rules are only a dozen sentences, they do not need to be paraphrased.
Peter N Lewis
2009-06-23 07:47:17
A:
Short answer: In the base class.
Long answer: Objects are "owned" by other objects. To own an object, you have to allocate or retain it (with retain, alloc, new, or copy). The owner is responsible for disposing of the memory with a release or autorelease. There should be one release/autorelease for every allocation/retain.
It is Cocoa convention that only methods that begin with "new" and "copy" return objects that have been allocated/copied/retained but are not owned by the method's receiver. The owner is then the object that called the "new" or "copy" function.
Tom Dalling
2009-06-23 06:41:50