Question

In my app, the singleton class (SharedData) allocates memory for a NSMutableArray:

[self sharedMutableArray] = [[NSMutableArray alloc] init];

Class A populates the this sharedMutableArray:

NSObject *obj = [NSObject alloc] init];
[sharedMutableArray  addObject];
obj = nil;

Class B does this – and that’s my question:

NSMutableArray *tmpArray = sharedMutableArray;
       ... uses the tmpArray locally
[tmpArray removeAllObjects];
tmpArray = nil;

This is an inherited code and my hunch is that this is a NO-NO. Can some one confirm that assigning nil to tmpArray will release memory for sharedMutableArray also…. I guess the author wanted to release tmpArray only…

Answer 1

Assigning nil to tmpArray only sets your pointer to the object to nil. It does not affect the object itself (or its lifecycle) at all. In this case, setting the objects you’ve created to nil does nothing, since their variable declaration is in local scope – if you want the objects to be deallocated from memory you need to send them release before setting the pointer to the object to nil.

However, sending removeAllObjects is affecting your original sharedArray, because you didn’t copy the array, you simply set a new pointer to point to the ‘singleton’. You probably want this:

NSMutableArray *tmpArray = [NSMutableArray arrayWithArray:sharedMutableArray];

You won’t need to use removeAllObjects in the above case because it will be autorelease’d. I suggest you read this.