How to add alive object to NSMutableArray and remove them when they're released?

Question

I have class Item and class List (which has an NSMutableArray).

Every time class Item is instantiated (and destroyed) it posts a notification, which is listened-to b

Answer 1

I haven’t tested this, so comments are welcome.

You could use an NSPointerArray for the list (in a retain property):

self.array = [NSPointerArray pointerArrayWithWeakObjects];

When an Item object is created, it would post a notification that’s listened by your List class. Upon receiving the notification, List adds the object to the pointer array:

[array addPointer:pointerToTheObject];

In this setting, the pointer array doesn’t keep a strong reference to its elements — in particular, it doesn’t retain them. This applies to both garbage-collected and non-garbage-collected builds.

In a garbage-collected build, if an element is garbage collected then the garbage collector automatically assigns NULL to the position in the array where the object was stored.

In a non-garbage-collected build, you’ll need to manually remove the element or assign NULL to the position in the array where it was stored. You can do this by overriding -[Item dealloc] and posting a notification that the object is being deallocated. Your List class, upon receiving the notification, would act upon it.

Note that, since objects are not owned by the pointer array, you must keep a strong reference to (or retain) them if you want to keep them alive.