How to disable a UINavigationBarItem?

I'm trying to disable a button that I add to my navigation cont开发者_JS百科roller bar. Here is how I added it:

UIBarButtonItem *addButton = [[UIBarButtonItem alloc] initWithTitle:@"Add" style:UIBarButtonItemStylePlain target:self action:@selector(addNew)];          
self.navigationItem.rightBarButtonItem = addButton;
[addButton release];

What is the best way to enable/disable items like these? I've tried this code:

addButton.disabled = YES;

but it doesn't work of course. Any help would be appreciated. Thanks.

Edit: Should be addButton.enabled = YES;

Oops

If you define addButton in your header, and @synthesize it, then you will be able to use addButton.enabled = NO;, there is no "disabled" setter.

.h

@interface MyViewController {
    UIBarButtonItem *addButton;
}
@property(nonatomic,retain) UIBarButtonItem *addButton;
@end

.m

@implementation MyViewController
@synthesize addButton;

-(void)viewDidLoad{
    addButton = [[UIBarButtonItem alloc] initWithTitle:@"Add" style:UIBarButtonItemStylePlain target:self action:@selector(addNew)];          
    self.navigationItem.rightBarButtonItem = addButton;
    [addButton release];
}
-(void)DoSomething{
    addButton.enabled = NO;
}