setting objects to nil when releasing NSArray

Question

When I get a memory warning I am releasing a bunch of objects stored in an NSMutableArray.

[_children release];

I also need to recurse through objects at some point (potentially after a mem warning has happened), so I need to check if the objects are still around, which I do with comparison to nil- which isn't going to work because releasing the array doesn't nil anything.

I can't loop through the array removing objects 1-by-1 and setting to nil because I'm not allowed to modify an array during iteration.

It feels like I'm missing something obvious. I just want to release + nil some values in an array.

Answer 1

Assuming that you aren't retaining the array elements elsewhere, surely by removing an object from the array, or releasing the array itself you are also releasing the element(s). I think that is as much as you need to do.

From the Apple documentation:

each object receives a retain message before its id is added to the array and a release message when it is removed from the array or when the array is deallocated

Answer 2

Sorry, but what you are doing seems pointless to me. You cannot set an object to nil, you can only set the reference to an object to nil, but that has on influence on other references.

NSObject * a = [[NSObject alloc] init];
NSObject * b = a;

[a release];
a = nil;

// b is NOT nil! b still points to the memory location where
// a used to be, which is now not valid anymore and using b
// for anything may crash your application!

If I put "a" into an array and then remove it again from the array, the retain count of "a" is decreased by one. Either it is then still bigger than zero, in which case "a" will not be released or it is zero, in which case it is released. Setting the reference to a to nil after it was released has no influence on other variables still pointing to "a".

So even if NSArray was setting the reference to "a" to nil after removing it to the array and releasing it (because its ref count got zero), it will have no affect on an instance variable still pointing to "a".

I'm not really sure what you are trying to do and it is certainly possible, but you are on a totally wrong track here.