[SOLVED] iPhone SDK : UIBarButtonItem not refreshing after Memory warning

I'm facing a very strange behavior of UIBarButtonItem.

I have been able to reproduce the bug in a test app whose code has been pasted below.

On my first view I have a label displaying a GUID, a button to go to an empty second view, and a UIBarButtonItem. If I click it its color changes from green to red and vice versa and the GUID updates.

Here is how to reproduce it:

go to the second view
raise a memory warning (in the Simulator Hardware menu, but works the same with a real memory warning on the device)
go back to the first one
click the UIBarButtonItem

The UIBarButtonItem is not refreshing even if it was before and logs show everything seems correct.

ViewController.h

#import <UIKit/UIKit.h>

@interface ViewController : UIViewController {
    @private
    BOOL _isGreenNotRed;
}

@property (weak, nonatomic) IBOutlet UIBarButtonItem *aButton;
@property (weak, nonatomic) IBOutlet UILabel *aGUID;
@end

ViewController.m

#import "ViewController.h"
#import "AFHTTPClient.h"
#import "AFHTTPRequestOperation.h"

@interface ViewController ()
- (NSString *)generateUUID;
- (void)refreshView;
@end

@implementation ViewController
@synthesize aButton;
@synthesize aGUID;

- (NSString *)generateUUID
{
    CFUUIDRef theUUID = CFUUIDCreate(NULL);
    CFStringRef string = CFUUIDCreateString(NULL, theUUID);
    CFRelease(theUUID);
    return (__bridge_transfer NSString *)string;
}

-(void)refreshView {
    NSLog(@"Refreshing first view");

    if(self->_isGreenNotRed) {
        [self.aButton setTintColor:[UIColor colorWithRed:0. green:0.8 blue:0. alpha:1.]];
        NSLog(@"Button should be green");
    }
    else {
        [self.aButton setTintColor:[UIColor colorWithRed:0.8 green:0. blue:0. alpha:1.]];
        NSLog(@"Button should be red");
    }

    self->_isGreenNotRed = !self->_isGreenNotRed;

    NSString *guid = [self generateUUID];

    [self.aGUID setText:guid];
    NSLog(@"GUID should be %@", guid);
}

- (IBAction)aButtonClick:(id)sender {
    [self refreshView];
}

#pragma mark - View lifecycle

- (void)viewDidLoad
{
    [super viewDidLoad];
    // Do any additional setup after loading the view, typically from a nib.
    self->_isGreenNotRed = YES;
    [self refreshView];
}

- (void)viewDidUnload
{
    [self setAButton:nil];
    [self setAGUID:nil];
    [super viewDidUnload];
    // Release any retained subviews of the main view.
}

- (BOOL)shouldAutorotateToInterfaceOrientation:(UIInterfaceOrientation)interfaceOrientation
{
    if ([[UIDevice currentDevice] userInterfaceIdiom] == UIUserInterfaceIdiomPhone) {
        return (interfaceOrientation != UIInterfaceOrientationPortraitUpsideDown);
    } else {
        return YES;
    }
}

-(void)prepareForSegue:(UIStoryboardSegue *)segue sender:(id)sender {
    NSLog(@"Going to second view");
}

@end

And the storyboard :

storyboard

It affects Simulator 5.0 and 5.1, and Device on 5.1.1

EDIT : by logging the value of self.aButton I saw it became nil after the memory warning, due to the weak keyword. But how can I reassign it ? Shouldn't the SDK do it by itself ? And why is aGUID still available ?

EDIT : here is a log. we can see aButton becomes nil.

2012-07-19 14:39:14.716 test[934:f803] Refreshing first view
2012-07-19 14:39:14.718 test[934:f803] Button <UIBarButtonItem: 0x68b89d0> should be green
2012-07-19 14:39:14.719 test[934:f803] GUID label <UILabel: 0x6dbe580; frame = (49 291; 222 48); text = '08960AFD-F98A-4FBA-9A6E-C...'; clipsToBounds = YES; opaque = NO; autoresize = RM+BM; userInteractionEnabled = NO; layer = <CALayer: 0x6dbe5f0>> should be 08960AFD-F98A-4FBA-9A6E-C548E753F259
2012-07-19 14:39:18.690 test[934:f803] Refreshing first view
2012-07-19 14:39:18.692 test[934:f803] Button <UIBarButtonItem: 0x68b89d0> should be red
2012-07-19 14:39:18.692 test[934:f803] GUID label <UILabel: 0x6dbe580; frame = (49 291; 222 48); text = 'EBB41B52-46D1-4CAE-BF0E-B...'; clipsToBounds = YES; opaque = NO; autoresize = RM+BM; userInteractionEnabled = NO; layer = <CALayer: 0x6dbe5f0>> should be EBB41B52-46D1-4CAE-BF0E-B0679BC1F0EE
2012-07-19 14:39:19.946 test[934:f803] Refreshing first view
2012-07-19 14:39:19.949 test[934:f803] Button <UIBarButtonItem: 0x68b89d0> should be green
2012-07-19 14:39:19.949 test[934:f803] GUID label <UILabel: 0x6dbe580; frame = (49 291; 222 48); text = '8E802026-E825-4219-9CCA-5...'; clipsToBounds = YES; opaque = NO; autoresize = RM+BM; userInteractionEnabled = NO; layer = <CALayer: 0x6dbe5f0>> should be 8E802026-E825-4219-9CCA-5106BF65BDA0
2012-07-19 14:39:33.353 test[934:f803] Going to second view
2012-07-19 14:39:40.811 test[934:f803] Received memory warning.
2012-07-19 14:39:43.471 test[934:f803] Refreshing first view
2012-07-19 14:39:43.472 test[934:f803] Button (null) should be green
2012-07-19 14:39:43.473 test[934:f803] GUID label <UILabel: 0x6896570; frame = (49 291; 222 48); text = '3D4933A8-908B-4570-BD55-6...'; clipsToBounds = YES; opaque = NO; autoresize = RM+BM; userInteractionEnabled = NO; layer = <CALayer: 0x68b0130>> should be 3D4933A8-908B-4570-BD55-68C298F6E621
2012-07-19 14:39:48.649 test[934:f803] Refreshing first view
2012-07-19 14:39:48.650 test[934:f803] Button (null) should be red
2012-07-19 14:39:48.651 test[934:f803] GUID label <UILabel: 0x6896570; frame = (49 291; 222 48); text = '9CDCF065-12C2-4F16-9464-A...'; clipsToBounds = YES; opaque = NO; autoresize = RM+BM; userInteractionEnabled = NO; layer = <CALayer: 0x68b0130>> should be 9CDCF065-12C2-4F16-9464-A5CE202BE7CA