Question

This is a basic question, and I’m not really sure what to search for to see if its been asked before.

In a lot of examples, I’ve seen property assignments handled like this:

NSArray *tempArray = [/*some code to get array*/];
self.propertyArray = tempArray;
[tempArray release];

Why not just do:

self.propertyArray = [/*some code to get array*/];

What’s the difference between the two?

Answer 1

This answer is assuming your not using ARC.

The first code snippet, is the way Apple recommends initializing a property as long as you are doing this in any method besides init. You’ll notice Apple code snippets do this a lot. It makes it much easier to manage your memory, and in my opinion it makes it easier to read.

NSArray *tempArray = [[NSArray alloc] initWith....]
self.propertyArray = tempArray;
[tempArray release];

The second code snippet you have could potential lead to a memory leak depending how you set up the NSArray.

This would be a leak. The propertyArray would have an retain count of 2. After you release the instance variable in dealloc, you still have a retain count of 1. That is a leak.

self.propertyArray = [[NSArray alloc] initWith...];

This would be okay, because they both are being autoreleased, which would give you a retain count of 1. As, long as you release the instance variable in dealloc.

// Class Method so autoreleased
self.propertyArray = [NSArray arrayWith....];

// Explicitly declaring autorelease
self.propertyArray = [[[NSArray alloc] initWith.....] autorelease];

It’s simply just a matter of preference. I prefer the first way, I think it is easier to to read and follow.

Edit (with ARC):

All these methods would be acceptable with the exception of the release statement and autorelease statement.

[tempArray release];

ARC automatically takes care of the memory management for you, so you do not have to explicitly release them. This is the benefit of ARC, you can create as many objects as you want without the headache of trying to figure out where to release them.

Also, your property would be different. You must either use strong or weak, and not retain. In this case strong would be the solution.

@property (nonatomic, strong) NSArray *tempArray;