Can't add button on navigation bar

I have UItable with items. I have navigation bar etc. On one item in table "Category" I pust another UITable like this:

CategoryTableViewController *b = [[CategoryTableViewController alloc]init];
        [self.navigationController pushViewController:b animated:YES];
        [b release];

Now I want to add "ADD" button in navigation bar and I add UINavigationBarItem in *.xib conn开发者_如何学运维ect it to outlets and add it like this in viewDidLoad:

self.navigationItem.rightBarButtonItem = self.addButton;

And this does not work (addButton is null), but when I put the same code for adding button in my first UITable it works fine and "ADD" button is added.

What could be the problem here?

In the ViewController that should show the button in the navigation bar type in the viewDidLoad() method:

self.addToolbarButton = [[[UIBarButtonItem alloc]           
initWithTitle:@"Add", nil)
    style:UIBarButtonSystemItemAdd 
    target:self
    action:@selector (add)] autorelease];
self.navigationItem.leftBarButtonItem = addToolbarButton;

That will add a "add" styled button to the left in the navigation bar which calls the selector method:

-(void) add {...}

in the same class when it is tapped. In this method in the same class you can specify your add logic. If this method should be placed in a different class, set the target to that.

That is the programatical way to solve this. The method "-(void) add" is what your Outlet has been in the .xib approach.

For your .xib approach you should verify that the Outlet property for the navigationBarButton is set to retain.

self.addButton is NULL, thus make sure its not NULL. Create a button from code.

UIBarButtonItem *button = [[UIBarButtonItem alloc] initWithBarButtonSystemItem:UIBarButtonSystemItemDone target:self action:@selector(doneMeasuring:)];

is [super viewDidLoad]; the first call in your viewDidLoad method?

If not try to put it at the very beginning of viewDidLoad.