iPhone SDK : UIBarButtonItem not refreshing after Memory warning

Question

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 :

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

Answer 1

Is refreshView getting called after the memory warning?

Try removing the code that sets the views to nil in viewDidUnload ? Does it solve the problem?