Strange Crash when dismissing view controller, auto-layout to blame?

Question

I am experiencing a very strange crash, here is the backtrace.

* thread #1: tid = 0x2403, 0x3379516c CoreFoundation`CFHash + 8, stop reason = EXC_BREAKPOINT (code=EXC_ARM_BREAKPOINT, subcode=0xdefe)
    frame #0: 0x3379516c CoreFoundation`CFHash + 8
    frame #1: 0x33797a9c CoreFoundation`CFBasicHashRemoveValue + 1408
    frame #2: 0x337974ee CoreFoundation`CFDictionaryRemoveValue + 166
    frame #3: 0x3420988e Foundation`-[NSISEngine removeConstraintWithMarker:] + 562
    frame #4: 0x34211dbe Foundation`-[NSLayoutConstraint _removeFromEngine:] + 230
    frame #5: 0x35a954ec UIKit`-[UIView(UIConstraintBasedLayout) _layoutEngine_willRemoveLayoutConstraint:] + 44
    frame #6: 0x358488fc UIKit`__48-[UIScrollView _setAutomaticContentConstraints:]_block_invoke_0 + 148
    frame #7: 0x34208882 Foundation`-[NSISEngine withAutomaticOptimizationDisabled:] + 166
    frame #8: 0x35848838 UIKit`-[UIScrollView _setAutomaticContentConstraints:] + 116
    frame #9: 0x35848e6c UIKit`-[UIScrollView _rememberDependentConstraint:] + 112
    frame #10: 0x35a9e3ae UIKit`___updateViewDependenciesForConstraint_block_invoke_0 + 30
    frame #11: 0x35a954ba UIKit`_updateViewDependenciesForConstraint + 202
    frame #12: 0x35a953da UIKit`-[UIView(UIConstraintBasedLayout) _layoutEngine_didAddLayoutConstraint:roundingAdjustment:mutuallyExclusiveConstraints:] + 154
    frame #13: 0x35a95534 UIKit`-[UIView(UIConstraintBasedLayout) _tryToAddConstraintWithoutUpdatingConstraintsArray:roundingAdjustment:mutuallyExclusiveConstraints:] + 36
    frame #14: 0x3567c2e0 UIKit`-[UIView(Internal) _didMoveFromWindow:toWindow:] + 376
    frame #15: 0x356d34fe UIKit`-[UIScrollView _didMoveFromWindow:toWindow:] + 50
    frame #16: 0x3567c5c6 UIKit`-[UIView(Internal) _didMoveFromWindow:toWindow:] + 1118
    frame #17: 0x35676e52 UIKit`-[UIView(Hierarchy) _postMovedFromSuperview:] + 138
    frame #18: 0x3565e7dc UIKit`-[UIView(Internal) _addSubview:positioned:relativeTo:] + 1300
    frame #19: 0x3565e2c2 UIKit`-[UIView(Hierarchy) addSubview:] + 30
    frame #20: 0x356f68e8 UIKit`-[UITransitionView transition:fromView:toView:removeFromView:] + 972
    frame #21: 0x35937618 UIKit`__91-[UIWindowController transition:fromViewController:toViewController:target:didEndSelector:]_block_invoke_0238 + 388
    frame #22: 0x357499b8 UIKit`-[UIWindowController transition:fromViewController:toViewController:target:didEndSelector:] + 4824
    frame #23: 0x357b9814 UIKit`-[UIViewController _dismissViewControllerWithTransition:from:completion:] + 1708
    frame #24: 0x357057c4 UIKit`-[UIViewController dismissViewControllerWithTransition:completion:] + 912
    frame #25: 0x000ccd40 Capture`-[INFTagSearchViewController cancelButtonTouched:](self=0x1f09ed50, _cmd=0x001b9d5f, sender=0x1e0265c0) + 76 at INFTagSearchViewController.m:48
    frame #26: 0x357470c4 UIKit`-[UIApplication sendAction:to:from:forEvent:] + 72
    frame #27: 0x35747076 UIKit`-[UIApplication sendAction:toTarget:fromSender:forEvent:] + 30
    frame #28: 0x35747054 UIKit`-[UIControl sendAction:to:forEvent:] + 44
    frame #29: 0x3574690a UIKit`-[UIControl(Internal) _sendActionsForEvents:withEvent:] + 502
    frame #30: 0x35746e00 UIKit`-[UIControl touchesEnded:withEvent:] + 488
    frame #31: 0x3566f5f0 UIKit`-[UIWindow _sendTouchesForEvent:] + 524
    frame #32: 0x3565c800 UIKit`-[UIApplication sendEvent:] + 380
    frame #33: 0x3565c11a UIKit`_UIApplicationHandleEvent + 6154
    frame #34: 0x373655a2 GraphicsServices`_PurpleEventCallback + 590
    frame #35: 0x373651d2 GraphicsServices`PurpleEventCallback + 34
    frame #36: 0x33829172 CoreFoundation`__CFRUNLOOP_IS_CALLING_OUT_TO_A_SOURCE1_PERFORM_FUNCTION__ + 34
    frame #37: 0x33829116 CoreFoundation`__CFRunLoopDoSource1 + 138
    frame #38: 0x33827f98 CoreFoundation`__CFRunLoopRun + 1384
    frame #39: 0x3379aebc CoreFoundation`CFRunLoopRunSpecific + 356
    frame #40: 0x3379ad48 CoreFoundation`CFRunLoopRunInMode + 104
    frame #41: 0x373642ea GraphicsServices`GSEventRunModal + 74
    frame #42: 0x356b0300 UIKit`UIApplicationMain + 1120
    frame #43: 0x000a297c Capture`main(argc=1, argv=0x2fd60cfc) + 116 at main.m:16
    frame #44: 0x3bb2bb20 libdyld.dylib`start + 4

You will notice frame 25 is the only call my code makes, and it is cancelButtonTouched which looks like.

- (IBAction)cancelButtonTouched:(id)sender {
    [self dismissViewControllerAnimated:YES completion:nil];
}

I am at a loss as to what is going on, I've never had an issue like this before, based on the system calls it appears to be an auto-layout issue. I verified that viewWillApper is called on the presenting view controller before the crash occurs, so I assume it is an issuing during layout of the presenting view.

Any ideas on how to narrow this issue down to a specific layout contstraint? Or any other ideas?

This is reproduceable on some devices, where as on others it rarely if ever happens. So it is intermittent.

Update

Screenshot of breakpoint.

Update 2

So it is definitely an issue with dismissing to the presentingViewController, dismissing two levels deep ([self.presentingViewController.presentingViewController dismissViewControllerAnimated:YES completion:nil]) works fine, but obviously not the desired result, I only want to go back 1 level. This further leads me to believe there is an issue "re-laying" out the view.

Answer 1

I seem to remember something like this, though not sure it was the exact same thing. In my case, it was caused by calling addSubview: (or insertSubview:...) with a view which already was a subview. While normally I think UIView deals with that, with auto layout it seems that it's possible for some associated information to be added elsewhere twice, and there can be a crash when trying to clean out that associated information. In my case, the solution was to ensure that I only added subviews once, and this crash (or my similar one anyways) went away.

Answer 2

Based on idea of Carl Lindberg I prepared and used the following iOS category and I have no crash anymore:

UIView+AddSubviewWithRemovingFromParent.h

#import <UIKit/UIKit.h>

@interface UIView (AddSubviewWithRemovingFromParent)

- (void)addSubviewWithRemovingFromParent:(UIView *)view;

@end

UIView+AddSubviewWithRemovingFromParent.m

#import "UIView+AddSubviewWithRemovingFromParent.h"

@implementation UIView (AddSubviewWithRemovingFromParent)

- (void)addSubviewWithRemovingFromParent:(UIView *)view {
    if (view.superview != nil) {
        [view removeFromSuperview];
    }
    [self addSubview:view];
}

@end

now you can use the addSubviewWithRemovingFromParent method to add the subView instead of addSubview method like this:

UITableViewCell *cell = [[UITableViewCell alloc] init];
[cell.contentView addSubviewWithRemovingFromParent:<viewToAdd>];

To sum it up:

1. find all references of addSubView in your controllers where the app is crashing
2. import the category UIView+AddSubviewWithRemovingFromParent.h
3. use method addSubviewWithRemovingFromParent instead of addSubView