Question

Trying to modify title in a UINavigationItem

// this modify the title
self.navigationItem.title    = @"Any title";
// this does not
navigationItem.title    = @"Any title";

Why?

Answer 1

navigationItem is not the object it’s using. self.navigationItem is a readonly property created on demand when using a UIViewController with a UINavigationController. You can certainly create custom UINavigationItem but thats often frowned upon in a standard UINavigationController setup, and you shouldn’t need to.

As for self.title, its merely a shortcut to self.navigationItem.title. The reason for the shortcut is it can be used elsewhere in other containment types if necessary including you own custom containers.

If you deconstruct what is happening. it is likely that this is happening, loading your title if you access a navigationItem, which a basic UINavigationController would:

- (UINavigationItem)navigationItem
{
    if (!_navigationItem) {
        _navigationItem = [[UINavigationItem alloc] initWithTitle:self.title];
    }

    return _navigationItem;
}

You can read more on what Apple has to say about it here: http://developer.apple.com/library/ios/#documentation/uikit/reference/UIViewController_Class/Reference/Reference.html#//apple_ref/occ/instp/UIViewController/navigationItem