Question

I am new to Objective-C and still don’t completely grasp the memory management. I have an NSMutableArray of pointers…

NSMutableArray *itemArray;

throughout my program, I add items to it.

//start loop    
MyItem *x = [[MyItem alloc] init];
[itemArray addObject:x];
//end loop

There comes a point when I want to toss all items in the array and re-populate it. Do I just loop through the whole array and send a release message to every object in the array as my intuition tells me, and then removeAllObjects, or does removeAllObjects take care of decrementing all the reference counts? Is the following correct?

//start loop
[[itemArray objectAtIndex:i] release];
//end loop
[itemArray removeAllObjects];

Answer 1

The real problem you have is this:

//start loop    
MyItem *x = [[MyItem alloc] init];
[itemArray addObject:x];
//end loop

You’re allocating an object (so you have ownership), then sticking it in the array and never releasing it. You should do this:

//start loop    
MyItem *x = [[MyItem alloc] init];
[itemArray addObject:x];
[x release];
//end loop

or this:

//start loop    
MyItem *x = [[[MyItem alloc] init] autorelease];
[itemArray addObject:x];
//end loop

Once you add it to the array, the array will take ownership by retaining the object, so you don’t have to keep it retained yourself. And when you call -removeAllObjects, the array will release them as appropriate. Basically, once you hand it off to the array, you don’t have to worry about it.

<Obligatory ARC plug>

You should start getting used to using ARC, where you won’t have to worry about releasing the object at all, because the compiler will do it for you.