Question

Why do I get a crash "Terminating app due to uncaught exception 'NSRangeException', reason: '*** -[__NSArrayM objectAtIndex:]: index 2 beyond bounds [0 .. 1]" after setting rightBarButtonItem?

In my app, I have three buttons on the right hand side, one of which should alternate with the systemEditButton. So I set the buttons up withrightBarButtonItems (note the “s”) and then change the right-hand one using rightBarButtonItem when appropriate.

With 5.0, Apple lets you set multiple items in the leftBarButtonItems and rightBarButtonItems of a NavigationBar. It also says you can change the outer one with leftBarButtonItem and rightBarButtonItem respectively (“The first item in the array can also be set using the rightBarButtonItem property”).

Works fine the first time, but then it crashes when I put back the original button. Even worse, it doesn’t object when I set it, it crashes later during the animation of UINavigationBar layoutSubViews. Checking rightBarButtonItems after setting rightBarButtonItems shows it correctly updated the array, but it crashes during layout.

Answer 1

Well, I’ve confirmed this with a test program (see below), and submitted a bug-report to Apple. The workaround is to read the Items array and hand it back a new one with the zeroth element updated.

//
//  ViewController.m
//  testBarButton
//
//  Created by Hugh Mackworth on 3/4/12.
//  Copyright (c) 2012 PineTree Software. All rights reserved.
//
#import "ViewController.h"
//#import <UIKit/UIKit.h>
//
//@interface ViewController : UIViewController {
//    
//@private
//    UIBarButtonItem * itemA;
//}
//
//@property (strong, nonatomic) UIBarButtonItem * itemA;
//
//@end

@implementation ViewController

@synthesize itemA;  //@property (strong, nonatomic) UIBarButtonItem * itemA;

-(void) reportButtons {
    NSLog (@"buttons:  %@",self.navigationItem.rightBarButtonItems);
}

-(void) itemA:(id) sender {
    NSLog(@"itemA hit");
   [self reportButtons];
}

-(void) itemB:(id) sender {
    NSLog(@"itemB hit");
    self.navigationItem.rightBarButtonItem = self.itemA;
    [self reportButtons];
}

-(void) itemC:(id) sender {
    NSLog(@"itemC hit");
    self.navigationItem.rightBarButtonItem = self.editButtonItem;
    [self reportButtons];
}

-(void) loadView {
    self.view = [[UIView alloc] initWithFrame: [[UIScreen mainScreen] bounds]];
    self.itemA = [[UIBarButtonItem alloc] initWithTitle:NSLocalizedString(@"Alternative Edit",@"")
                                                              style:UIBarButtonItemStyleBordered
                                                             target:self
                                                             action:@selector(itemA:)]; 
    UIBarButtonItem *itemB = [[UIBarButtonItem alloc] initWithTitle:NSLocalizedString(@"B-Hit Second",@"")
                                                              style:UIBarButtonItemStyleBordered
                                                             target:self
                                                             action:@selector(itemB:)]; //fix with itemB2:
    UIBarButtonItem *itemC = [[UIBarButtonItem alloc] initWithTitle:NSLocalizedString(@"C-Hit First",@"")
                                                              style:UIBarButtonItemStyleBordered
                                                             target:self
                                                             action:@selector(itemC:)]; //fix with itemC2:
    NSArray *rightItems = [NSArray arrayWithObjects: 
                           self.itemA,
                           itemB,
                           itemC,
                           nil];
    self.navigationItem.rightBarButtonItems = rightItems;
    [self reportButtons];                       

}

-(void) swapRightItem: (UIBarButtonItem *) newRightItem {
    NSMutableArray * newRightItems = [self.navigationItem.rightBarButtonItems mutableCopy];
    [newRightItems replaceObjectAtIndex:0 withObject: newRightItem];
    self.navigationItem.rightBarButtonItems = newRightItems;
    [self reportButtons];
}

-(void) itemB2:(id) sender {
    NSLog(@"itemB2 hit");
    [self swapRightItem:self.itemA];
}

-(void) itemC2:(id) sender {
    NSLog(@"itemC2 hit");
    [self swapRightItem:self.editButtonItem];
}

@end

//APP DELEGATE:
/*
 - (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions
{
    self.window = [[UIWindow alloc] initWithFrame:[[UIScreen mainScreen] bounds]];
    // Override point for customization after application launch.
    UIViewController * viewController = [[ViewController alloc] init];
    UINavigationController *watchNavController= [[UINavigationController alloc] initWithRootViewController:viewController ];

    self.window.rootViewController = watchNavController;
    [self.window makeKeyAndVisible];
    return YES;
}
*/