UIAlertView crashes when button tapped: how to solve?

Question

I have a class that I instance to show an alert view like this:

- (void)showAlert
{       
  UIAlertView *alertView = [[UIAlertView alloc] initWithTitle:@"Do you want to try again?"
                                                        message:nil
                                                       delegate:self
                                              cancelButtonTitle:@"Yes"
                                              otherButtonTitles:@"No", nil];

  [alertView show];
}

}

I need self to be the delegate because I need alertView:didDismissWithButtonIndex: to be called to perform some actions when the user taps the alert view's button. This usually works well, but from time to time, I get this crash:

SIGSEGV
UIKit-[UIAlertView(Private) modalItem:shouldDismissForButtonAtIndex:]

I guess this is because the delegate, for any reason, was released, right? Or is this because what was released was the alert view? How could I solve this? I need the alert view to have a delegate, and I've reading several related posts and I couldn't find an answer that fits my scenario.

I'm testing in iOS 7.0, I don`t know if that could have to do with the issue.

Thanks in advance

Please check if you are calling the alertview in the main thread? — Rose, Apr 02 '14 at 11:45
I always create the object that shows the alert view within a view controller. It is a strong property. Can I assume it is always called in the main thread, then? Unfortunately I don't know how to cause this crash intentionally — AppsDev, Apr 02 '14 at 11:53
@Gabriel.Massana if I check `[NSThread isMainThread]` before showing the alert view, will I prevent the app from reaching this crash? — AppsDev, Apr 02 '14 at 11:55
@AppsDev `[NSThread isMainThread]` is only to check if you are in the main thread. IS to check @Rose comment. — Gabriel.Massana, Apr 02 '14 at 11:57
please check dispatch_sync(dispatch_get_main_queue(), ^{ alertView show] }); — Rose, Apr 02 '14 at 12:15
@Rose I'm using TestFlight and the crash report says it is the `Primary Thread Thread 0` — AppsDev, Apr 02 '14 at 12:40

score 3 · Answer 1 · answered Apr 02 '14 at 11:46

It seems that you tap alert when its delegate is released:

delegate:self

It happens because UIAlertView delegate property is of assign type (not weak!). So your delegate potentially can point to released object.

Solution:

in dealloc method you need to clear delegate for your alertView

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

But before you need to make iVar _alertView and use it for your alertViews

- (void)showAlert
{       
     _alertView = ...;

     [_alertView show];
}

score 0 · Answer 2 · answered Apr 02 '14 at 13:24

0

Update your code as follows:

- (void)showAlert {       
  UIAlertView *alertView = [[UIAlertView alloc] initWithTitle:@"Do you want to try again?"
                                                        message:nil
                                                       delegate:self
                                              cancelButtonTitle:@"Yes"
                                              otherButtonTitles:@"No", nil];

  [alertView show];
}

Its due to you are missing the nil for otherButtonTitles part.

Missing sentinel in method dispatch warning will be shown if you didn't add nil.

answered Apr 02 '14 at 13:24

Sujith Thankachan

3,508
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Thanks, my fault... I actually have `nil` added but it seems I removed it from the code I pasted here, sorry. I'm going to edit it. – AppsDev Apr 02 '14 at 13:40
Is that still crashing? – Sujith Thankachan Apr 03 '14 at 03:47

score 0 · Answer 3 · answered Aug 20 '14 at 08:14

That's because the alertView's delegate object released while clicking the button. I think it's a bug of SDK:

@property(nonatomic,assign) id /*<UIAlertViewDelegate>*/ delegate;    // weak reference

should be:

@property(nonatomic, weak) id /*<UIAlertViewDelegate>*/ delegate;    // weak reference

To fix the issue:

add a weak delegate for UIAlertView using association.
swizzle the init, setDelegate: delegate methods, set alertView delegate to self, set step 1 weak delegate with the param delegate.
implement all delegate methods, deliver the methods using the weak delegate.

UIAlertView crashes when button tapped: how to solve?

3 Answers3