iOS 7 bug or my bug in UIAlertView

I have got the following stack trace while my app crashes on tapping "OK" on a UIAlertView. Is it my fault or a iOS7 bug? I don't know how to fix this.

OS Version:          iOS 7.0 (11A465)
Report Version:      104

Exception Type:  EXC_BAD_ACCESS (SIGSEGV)
Exception Subtype: KERN_INVALID_ADDRESS at 0x00000000
Triggered by Thread:  0

Thread 0 name:  Dispatch queue: com.apple.main-thread
Thread 0 Crashed:
0   libobjc.A.dylib                 0x39d50b36 objc_msgSend + 22
1   UIKit                           0x3212e3da -[UIAlertView(Private) modalItem:shouldDismissForButtonAtIndex:] + 58
2   UIKit                           0x31ed2036 -[_UIModalItemsCoordinator _notifyDelegateModalItem:tappedButtonAtIndex:] + 90
3   UIKit                           0x31ed1f3e -[_UIModalItemAlertContentView tableView:didSelectRowAtIndexPath:] + 890
4   UIKit                           0x31dd7326 -[UITableView _selectRowAtIndexPath:animated:scrollPosition:notifyDelegate:] + 1074
5   UIKit                           0x31e8a24e -[UITableView _userSelectRowAtPendingSelectionIndexPath:] + 210
6   UIKit                           0x31d3a96e _applyBlockToCFArrayCopiedToStack + 314
7   UIKit                           0x31cb246e _afterCACommitHandler + 426
8   CoreFoundation                  0x2f5141d2 __CFRUNLOOP_IS_CALLING_OUT_TO_AN_OBSERVER_CALLBACK_FUNCTION__ + 18
9   CoreFoundation                  0x2f511b74 __CFRunLoopDoObservers + 280
10  CoreFoundation                  0x2f511eb6 __CFRunLoopRun + 726
11  CoreFoundation                  0x2f47cce2 CFRunLoopRunSpecific + 518
12  CoreFoundation                  0x2f47cac6 CFRunLoopRunInMode + 102
13  GraphicsServices                0x3417727e GSEventRunModal + 134
14  UIKit                           0x31d1ea3c UIApplicationMain + 1132
15  MyApp                           0x000d8e5e 0xcb000 + 56926
16  libdyld.dylib                   0x3a25dab4 start + 0

Alert view code

UIAlertView *av = [[UIAlertView alloc] initWithTitle:@"Error"
    message:[NSString stringWithFormat:@"Es ist ein Fehler aufgetreten: %@", [error localizedDescription]]
    delegate:self
    cancelButtonTitle:@"OK"
    otherButtonTitles:nil];
[av show];

and I haven't defined a delegate method.

Solution 1:

Stupid me, I just have to set the alert view's delegate to nil

Solution 2:

Because the delegate of the UIAlertView is an assign property in UIAlertView. I think that it is Apple's fault. It should be a weak pointer in ARC. But it is an assign property so you need to set the any alert view's delegate to nil before destroying the delegate (most of the time a controller class got popped or navigated back). Read the .h file for UIAlertView about the delegate, you can find it is an assign property and someone commented after the declaration saying "//weak reference".

Solution 3:

The best way to avoid problem with UIAlertView while using delegation is to make instance of UIAlertView as iVar for delegate class. And after you should make delegate property of alertView as nil in dealloc of delegate class

@implementation YOUR_CLASS
{
    UIAlertView *_alert;
}

- (void)dealloc
{
    _alert.delegate = nil;
}


- (void)showAlertView
{
    _alert = [[UIAlertView alloc] initWithTitle:title message:message delegate:self cancelButtonTitle:@"OK" otherButtonTitles:nil];
    [alert show];
}

The same approach is good enough for all old classes with assign-type delegates.