CODEWITHSUNDEEP
iphoneobjective-cmemory-leaks
user176891
user176891

Reputation:

Objective C memory leak issue

The Leaks instrument tells me that I have a leak in this code fragment. Why is this so?

This code fragment is in viewDidLoad().

UINavigationItem *navItem=[self navigationItem];

UIBarButtonItem *addFeed = [[UIBarButtonItem alloc] initWithBarButtonSystemItem:UIBarButtonSystemItemAdd target:self action:@selector(addFeed)];
[navItem setRightBarButtonItem:addFeed]; // leaks says that 128 bytes leaked
[addFeed release];

UIBarButtonItem *reload = [[UIBarButtonItem alloc] initWithBarButtonSystemItem:UIBarButtonSystemItemRefresh  target:self action:@selector(reload)];
[navItem setLeftBarButtonItem:reload]; // leaks says that 128 bytes leaked here too !
[reload release];
[navItem release];

Upvotes: 2

Views: 985

Answers (6)

Nick
Nick

Reputation: 19664

 [navItem setRightBarButtonItem:addFeed];

 [navItem setLeftBarButtonItem:reload];

You are creating copies of the objects in these accessors. These accessors are incrementing the retainCount by 1. Your accessors should release each object and then immediately retain them.

Example:

- (void) setTitle: (NSString*) newTitle {
    if (title != newTitle) {
        [title release];
        title = [newTitle retain]; // Or copy, depending on your needs.
    }

Take a look at the techniques here: Memory Management Programming

I believe that's what's up. So take a hard look at those two accessors.

Upvotes: 0

pxl
pxl

Reputation: 1297

if you're still getting the leak message and can't track down the bug, you can try using the static analyzer included in the latest and greatest Xcode (version 3.2)

Build > Build and Analyze

it'll use LLVM-Clang to statically analyze your code in a pretty way.

http://developer.apple.com/mac/library/featuredarticles/StaticAnalysis/index.html

UPDATE:

in your code snippet:

UINavigationItem *navItem=[self navigationItem];

UIBarButtonItem *addFeed = [[UIBarButtonItem alloc] initWithBarButtonSystemItem:UIBarButtonSystemItemAdd target:self action:@selector(addFeed)];
[navItem setRightBarButtonItem:addFeed]; // leaks says that 128 bytes leaked
[addFeed release];

your leak is probably coming from setting the new rightBarButtonItem without releasing the old one.

this is what i think is happening:

1) get a handle to the navigationItem (has right bar button A)

2) create a new UIBarButton Item (making right bar button B)

3) setRightBarButtonItem to button B

now where's Button A? it should have been released by navItem when you set the new button. so you could have forgotten to release the button when you set it the first time, or you've got it retained somewhere else.

Upvotes: 2

Valerii Hiora
Valerii Hiora

Reputation: 1552

It seems that you're not releasing the view controller with custom viewDidLoad method.

Upvotes: 0

nall
nall

Reputation: 16139

Do you have NSZombieEnabled? This causes objects not to be retained by the NSZombie instances and you'll see "leaks" when running the Leaks tool.

Upvotes: 0

Adam Rosenfield
Adam Rosenfield

Reputation: 400274

The leaks instrument only tells you where the leaked memory was allocated; it can't tell you where the memory should have been released but wasn't since there's no possible way for it to know that. Your leak is occurring elsewhere.

This code is mostly fine, except you should not be releasing navItem at the end. You are not an owner of it, since you didn't create it with a method named alloc, new, or copy in its name, so you should not release it.

Upvotes: 3

Dave DeLong
Dave DeLong

Reputation: 243156

You should not be releasing navItem. You did not alloc/retain/new/create it, so you do not release it.

Other than that, your code looks fine. Is that everything in the method?

Upvotes: 6

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