Obj-C, Potential leak of an object allocated on line, UIBarButtonItem alloc - objective-c

Question

I'm getting an analyser leak, however this is the same code i'm using elsewhere without a problem. I know I'm using alloc and therefore I have to release, but I am doing this in dealloc.
What am I doing wrong ?
Header file:
#interface myViewController : UIViewController <UITableViewDataSource,
UITableViewDelegate> {
UIBarButtonItem *addButton;
}
#property (nonatomic, retain) UIBarButtonItem *addButton;
Main file:
#synthesize addButton;
- (void)viewDidLoad {
NSMutableArray* buttons = [[NSMutableArray alloc] initWithCapacity:3];
addButton = [[UIBarButtonItem alloc]
initWithBarButtonSystemItem:UIBarButtonSystemItemAdd
target:self action:#selector(btnNavAddPressed:)];
addButton.style = UIBarButtonItemStyleBordered;
[buttons addObject:addButton];
[tools setItems:buttons animated:NO];
[buttons release];
self.navigationItem.rightBarButtonItem = [[UIBarButtonItem alloc]
initWithCustomView:tools];
addButton.enabled = FALSE;
- (void)dealloc {
[addButton release];

Answer 1

when you use a property and assign to it the attributes you specified determine whether retainCount is incremented if you assign to the property. In your case you specified "retain" which means that the setter function that handles assignment to your property will automatically increment the retain count for the object.
However when you write
addButton = [[UIBarButtonItem alloc]
initWithBarButtonSystemItem:UIBarButtonSystemItemAdd
target:self action:#selector(btnNavAddPressed:)];
you are creating an opject with already retain count == 1 so when you assign it will have retain count 2. the proper way to do this is to create a temp variable and create the object, then assign the temp variable to the property thereafter releasing the temp. variable:
UIBarButtonItem* tmp = [[UIBarButtonItem alloc]
initWithBarButtonSystemItem:UIBarButtonSystemItemAdd
target:self action:#selector(btnNavAddPressed:)];
self.addButton = tmp;
[tmp release];
of course i would recommend a more descriptive name than 'temp' as variable name.

Answer 2

You are not using the setter, the code should be:
self.addButton = [[[UIBarButtonItem alloc]
initWithBarButtonSystemItem:UIBarButtonSystemItemAdd
target:self action:#selector(btnNavAddPressed:)] autorelease];
This type of problem can be avoided by using an ivar that has a different name than the property name. This is accomplished in the #synthesize statement:
#synthesize addButton = _addButton;
This way any omission of self will result in an error message.
Here is a full implementation (except tools is undefined), the property addButton is handles in all places:
#interface myViewController : UIViewController <UITableViewDataSource, UITableViewDelegate> {
}
#property (nonatomic, retain) UIBarButtonItem *addButton;
#end
#implementation myViewController
#synthesize addButton = _addButton;
- (void)viewDidLoad {
NSMutableArray* buttons = [NSMutableArray array];
self.addButton = [[UIBarButtonItem alloc]
initWithBarButtonSystemItem:UIBarButtonSystemItemAdd
target:self action:#selector(btnNavAddPressed:)];
self.addButton.style = UIBarButtonItemStyleBordered;
[buttons addObject:self.addButton];
[tools setItems:buttons animated:NO];
self.navigationItem.rightBarButtonItem = [[[UIBarButtonItem alloc] initWithCustomView:tools] autorelease];
self.addButton.enabled = FALSE;
}
- (void)dealloc {
[_addButton release];
}
#end

Answer 3

Both the above answers are misleading. You don't need to use a setter, it's perfectly fine to assign objects directly to iVars. You do need to release anything you alloc or retain however. The problem you have is here:
self.navigationItem.rightBarButtonItem = [[UIBarButtonItem alloc] initWithCustomView:tools];
This line is alloc'ing a UIBarButtonItem instance and setting it to the rightBarButtonItem property of the navigationItem. That means the navigationItem is retaining the UIBarButtonItem and it is responsible for that retain. You are responsible for releasing it b/c of the alloc and you are not. Change the code to this:
self.navigationItem.rightBarButtonItem = [[[UIBarButtonItem alloc] initWithCustomView:tools] autorelease];
and this leak goes away.

Answer 4

You are not taking advantage of the declared property but I don't see any problem with addButton. The leak seems more in:
self.navigationItem.rightBarButtonItem =
[[UIBarButtonItem alloc] initWithCustomView:tools];
Just add autorelease and the leak will go away.