Question

I have a UITabBarController with two tabs. TAB A is a UIViewController, and TAB B is a UIViewController loaded from a nib.

I’m trying to make it that when i move from TAB B to TAB A, or from TAB B any other tab, I want to reset TAB B to its initial state. I do that by just creating a new one and replacing that in the viewControllers array. The problem is that after I reset the UIViewController I get an error along the lines of “message sent to deallocated instance. It’s usually one of these two errors:

*** -[AddCompetitionViewController isEqual:]: message sent to deallocated instance...
*** -[AddCompetitionViewController retain]: message sent to deallocated instance...

This happens right after I switch from TAB B back to TAB A.

This is the code that I’m using to replace the tab with my attempt to isolate the problem.

- (BOOL)tabBarController:(UITabBarController *)tabBarController shouldSelectViewController:(UIViewController *)viewController
{
    NSLog(@"Should Select: %@", viewController);
    return YES;
}

- (void)tabBarController:(UITabBarController *)tabBarController didSelectViewController:(UIViewController *)viewController
{
    NSLog(@"Did Select: %@", viewController);
    if ([viewController class] != [AddCompetitionViewController class]) {
        AddCompetitionViewController *ACViewController = [[AddCompetitionViewController alloc] initWithNibName:@"AddCompetition" bundle:[NSBundle mainBundle] andDancer:self.currentDancer];
        UITabBarItem *ACitem = [[UITabBarItem alloc] initWithTitle:@"Add Comp." image:[UIImage imageNamed:@"Addcomp.png"] tag:0];
        ACViewController.tabBarItem = ACitem;

        NSMutableArray *arr = [[NSMutableArray alloc] initWithArray:self.viewControllers];
        [arr replaceObjectAtIndex:1 withObject:ACViewController];
        [self setViewControllers:arr];
        NSLog(@"Replaced: %@", [arr objectAtIndex:1]);
    }
}

(I am using ARC)

Using the NSLogs, I’ve been able to determine that When I try to switch back to TAB A, the app is trying to reference the old, original UIViewController, and not the new one. tabBarController:didSelectViewController: is the last thing that is called, I don’t have anything coded that references the UIViewController after the replacement. I’ve also tried adding an exception breakpoint, but that just lists a bunch of hex data, then defaults to application main. Here are my logs:

2012-08-18 16:20:05.479 How's My Feisin'[4780:c07] Should Select: <AddCompetitionViewController: 0x78a5af0>
2012-08-18 16:20:05.489 How's My Feisin'[4780:c07] Did Select: <AddCompetitionViewController: 0x78a5af0>
2012-08-18 16:20:06.885 How's My Feisin'[4780:c07] Should Select: <CompetitionListViewController: 0x78a7550>
2012-08-18 16:20:06.887 How's My Feisin'[4780:c07] Did Select: <CompetitionListViewController: 0x78a7550>
2012-08-18 16:20:06.887 How's My Feisin'[4780:c07] Replaced: <AddCompetitionViewController: 0x6c5d0f0>
2012-08-18 16:20:09.290 How's My Feisin'[4780:c07] *** -[AddCompetitionViewController retain]: message sent to deallocated instance 0x78a5af0

And a backtrace:

* thread #1: tid = 0x1c03, 0x017cddee CoreFoundation`___forwarding___ + 206, stop reason = EXC_BREAKPOINT (code=EXC_I386_BPT, subcode=0x0)
frame #0: 0x017cddee CoreFoundation`___forwarding___ + 206
frame #1: 0x017cdcb2 CoreFoundation`_CF_forwarding_prep_0 + 50
frame #2: 0x0176e2c0 CoreFoundation`CFRetain + 96
frame #3: 0x01798ab9 CoreFoundation`CFArrayApplyFunction + 57
frame #4: 0x0072ffbb UIKit`_afterCACommitHandler + 255
frame #5: 0x0183b99e CoreFoundation`__CFRUNLOOP_IS_CALLING_OUT_TO_AN_OBSERVER_CALLBACK_FUNCTION__ + 30
frame #6: 0x017d2640 CoreFoundation`__CFRunLoopDoObservers + 384
frame #7: 0x0179e4c6 CoreFoundation`__CFRunLoopRun + 1174
frame #8: 0x0179dd84 CoreFoundation`CFRunLoopRunSpecific + 212
frame #9: 0x0179dc9b CoreFoundation`CFRunLoopRunInMode + 123
frame #10: 0x01c447d8 GraphicsServices`GSEventRunModal + 190
frame #11: 0x01c4488a GraphicsServices`GSEventRun + 103
frame #12: 0x0071f626 UIKit`UIApplicationMain + 1163
frame #13: 0x00002595 How's My Feisin'`main + 181 at main.m:16
frame #14: 0x000024d5 How's My Feisin'`start + 53

Any help figuring out this error, or finding a better place to replace the UIViewController would be great!
Thanks!

EDIT: I have found what is causing the issue, but still don’t have a way to fix it. Even though I’ve never seen a UITabBarController animate a view change, It apparently still preforms an animation. I managed to profile the app, and _afterCACommitHandler is preforming an extra release on the object.

EDIT: I’ve figured out a work around, I put another UIViewController between the tabBarController and the UIViewController for TAB B. Then had the new UIViewController reset the old one. It works, but it’s not the right way to do things. And I still don’t know what was causing the extra release.

Answer 1

I created a workaround that encapsulates the UIViewController for TAB B in another UIViewController. This intermediary controller is the delegate for the UITabBarController, and deallocates and recreates the UIViewController I want to reset on a tab change. This prevents a missing ViewController reference in the tab bar controller.

Here is the intermediary class:

.h file

#import <UIKit/UIKit.h>
#import "AddCompetitionViewController.h"
#import "Dancer.h"

@interface AddCompResetViewController : UIViewController <UITabBarControllerDelegate>
{
    BOOL willReset;
}

@property (nonatomic, retain) Dancer *currentDancer;
@property (nonatomic, retain) AddCompetitionViewController *ACViewController;

- (id)initWithDancer:(Dancer *)dancer andTabBarController:(UITabBarController *)aController;
@end

.m file

@implementation AddCompResetViewController
@synthesize currentDancer, ACViewController;

- (id)initWithDancer:(Dancer *)dancer andTabBarController:(UITabBarController* )aController;
{
    if ((self = [super init])) {
        self.currentDancer = dancer;
        //create first instance
        self.ACViewController = [[AddCompetitionViewController alloc] initWithNibName:@"AddCompetition" bundle:[NSBundle mainBundle] andDancer:self.currentDancer];
        self.ACViewController.theTabBarController = aController;
        [self.view addSubview:self.ACViewController.view];
        willReset = NO;
    }
    return self;
}

- (void)tabBarController:(UITabBarController *)tabBarController didSelectViewController:(UIViewController *)viewController
{
    //reset
    if (viewController != self) {
        AddCompetitionViewController *AViewController = [[AddCompetitionViewController alloc] initWithNibName:@"AddCompetition" bundle:[NSBundle mainBundle] andDancer:self.currentDancer];
        [self.ACViewController.view removeFromSuperview];
        self.ACViewController = nil;
        self.ACViewController = AViewController;
        [self.view addSubview:self.ACViewController.view];
        willReset = NO;
    } else if (viewController == self) {
        willReset = YES;
    }
}

- (BOOL)tabBarController:(UITabBarController *)tabBarController shouldSelectViewController:(UIViewController *)viewController
{
    if (viewController.tabBarItem.tag == 4) {
        [self.navigationController popToRootViewControllerAnimated:YES];
        return NO;
    } else {
        return YES;
    }
}