How do I hide/show the right button in the Navigation Bar

I need to hide the right button in the Navigation Bar, then unhide it after the user selects some options.

Unfortunately, the following doesn't work:

NO GOOD: self.navigationItem.rightBarButtonItem.hidden = YES;  // FOO CODE

Is there a way?

Hide the button by setting the reference to nil, however if you want to restore it later, you'll need to hang onto a copy of it so you can reassign it.

UIBarButtonItem *oldButton = self.navigationItem.rightBarButtonItem;
[oldButton retain];
self.navigationItem.rightBarButtonItem = nil;

//... later
self.navigationItem.rightBarButtonItem = oldButton;
[oldButton release];

Personally, in my apps I make my nav buttons into @properties, so that I can trash & recreate them at will, so something like:

//mycontroller.h
UIBarButtonItem *rightNavButton;
@property (nonatomic, retain) UIBarButtonItem *rightNavButton;

//mycontroller.m
@synthesize rightNavButton;
- (UIBarButtonItem *)rightNavButton {
    if (!rightNavButton) {
        rightNavButton = [[UIBarButtonItem alloc] init];
        //configure the button here
    }
    return rightNavButton;
}

//later, in your code to show/hide the button:
self.navigationItem.rightBarButtonItem = self.rightNavButton;

For Swift 3

if let button = self.navigationItem.rightBarButtonItem {
                    button.isEnabled = false
                    button.tintColor = UIColor.clear
                }`

Show:

[self.navigationItem.rightBarButtonItem.customView setAlpha:1.0];

Hide:

[self.navigationItem.rightBarButtonItem.customView setAlpha:0.0];

You can even animate its showing/hiding

[UIView animateWithDuration:0.2 animations:^{
        [self.navigationItem.rightBarButtonItem.customView setAlpha:1.0];

    }];

Set reference to nil:

current_controller_in_navcontroller.navigationItem.rightBarButtonItem =  nil;

Also be sure to call this in the controller currently shown by the navController, not for the navController itself.

Here's Matt's solution updated for Storyboards & ARC. Remember, IBOutlets are __weak by default, so you need to change that to strong for it not to be released too early.

@interface MAGTableViewController () <UITextFieldDelegate>

@property (strong, nonatomic) IBOutlet UIBarButtonItem *rightBarButton;

@end

@implementation MAGTableViewController

- (void)viewDidLoad
{
    [super viewDidLoad];

    [self.navigationItem setRightBarButtonItem:nil];
}

- (IBAction)rightBarButtonItemTapped:(id)sender
{
    [self.view endEditing:YES];
}

- (void)textFieldDidBeginEditing:(UITextField *)textField
{
    [self.navigationItem setRightBarButtonItem:self.rightBarButton];
}

- (void)textFieldDidEndEditing:(UITextField *)textField
{
    [self.navigationItem setRightBarButtonItem:nil];
}

@end