'Unable to create description in descriptionForLayoutAttribute_layoutItem_coefficient. Something is nil'

Question

First, I got 3 different UIViews to replace the detail view in Split View Controller on iPad storyboard

It runs on well on iOS8 iPad. But when I load one of the detail views, the app crashes when running in iOS7 and iOS 6 Simulator.

I only assume it is because of Auto layout on my Storyboard.

Does anyone know how to fix it?

2014-09-25 04:15:19.705 PSTappsperance[48327:60b] Pad AppDelegate ########
2014-09-25 04:15:27.869 PSTappsperance[48327:60b] *** Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: 'Unable to create description in descriptionForLayoutAttribute_layoutItem_coefficient. Something is nil'
*** First throw call stack:
(
0   CoreFoundation                      0x0000000110a5c495 __exceptionPreprocess + 165
1   libobjc.A.dylib                     0x00000001107af99e objc_exception_throw + 43
2   CoreFoundation                      0x0000000110a5c2ad +[NSException raise:format:] + 205
3   Foundation                          0x00000001104ec548 descriptionForLayoutAttribute_layoutItem_coefficient + 145
4   Foundation                          0x00000001104ec3bc -[NSLayoutConstraint equationDescription] + 216
5   Foundation                          0x00000001104ec831 -[NSLayoutConstraint description] + 297
6   CoreFoundation                      0x0000000110a1d1b9 -[NSArray descriptionWithLocale:indent:] + 345
7   Foundation                          0x000000011037e14e _NSDescriptionWithLocaleFunc + 64
8   CoreFoundation                      0x00000001109e1244 __CFStringAppendFormatCore + 7252
9   CoreFoundation                      0x0000000110a1f913 _CFStringCreateWithFormatAndArgumentsAux + 115
10  CoreFoundation                      0x0000000110a7fa5b _CFLogvEx + 123
11  Foundation                          0x00000001103ae276 NSLogv + 79
12  Foundation                          0x00000001103ae20a NSLog + 148
13  UIKit                               0x000000010f927097 -[UIView(UIConstraintBasedLayout_EngineDelegate) engine:willBreakConstraint:dueToMutuallyExclusiveConstraints:] + 62
14  Foundation                          0x00000001104e32ac -[NSISEngine handleUnsatisfiableRowWithHead:body:usingInfeasibilityHandlingBehavior:mutuallyExclusiveConstraints:] + 521
15  Foundation                          0x00000001104e49b1 -[NSISEngine tryUsingArtificialVariableToAddConstraintWithMarker:rowBody:usingInfeasibilityHandlingBehavior:mutuallyExclusiveConstraints:] + 353
16  Foundation                          0x000000011039c26b -[NSISEngine tryToAddConstraintWithMarker:expression:integralizationAdjustment:mutuallyExclusiveConstraints:] + 663
17  Foundation                          0x00000001104ed180 -[NSLayoutConstraint _addLoweredExpression:toEngine:integralizationAdjustment:lastLoweredConstantWasRounded:mutuallyExclusiveConstraints:] + 275
18  Foundation                          0x00000001103981b0 -[NSLayoutConstraint _addToEngine:integralizationAdjustment:mutuallyExclusiveConstraints:] + 204
19  UIKit                               0x000000010f923f41 __57-[UIView(AdditionalLayoutSupport) _switchToLayoutEngine:]_block_invoke_2 + 413
20  Foundation                          0x00000001104e529a -[NSISEngine withBehaviors:performModifications:] + 119
21  UIKit                               0x000000010f923d7d __57-[UIView(AdditionalLayoutSupport) _switchToLayoutEngine:]_block_invoke + 401
22  UIKit                               0x000000010f923bc3 -[UIView(AdditionalLayoutSupport) _switchToLayoutEngine:] + 197
23  UIKit                               0x000000010f923e57 __57-[UIView(AdditionalLayoutSupport) _switchToLayoutEngine:]_block_invoke_2 + 179
24  Foundation                          0x00000001104e529a -[NSISEngine withBehaviors:performModifications:] + 119
25  UIKit                               0x000000010f923d7d __57-[UIView(AdditionalLayoutSupport) _switchToLayoutEngine:]_block_invoke + 401
26  UIKit                               0x000000010f923bc3 -[UIView(AdditionalLayoutSupport) _switchToLayoutEngine:] + 197
27  UIKit                               0x000000010f3ab975 __45-[UIView(Hierarchy) _postMovedFromSuperview:]_block_invoke + 95
28  Foundation                          0x00000001104e529a -[NSISEngine withBehaviors:performModifications:] + 119
29  UIKit                               0x000000010f3ab889 -[UIView(Hierarchy) _postMovedFromSuperview:] + 321
30  UIKit                               0x000000010f3b52ac -[UIView(Internal) _addSubview:positioned:relativeTo:] + 1508
31  UIKit                               0x000000010f632778 -[UINavigationTransitionView transition:fromView:toView:] + 454
32  UIKit                               0x000000010f6325b0 -[UINavigationTransitionView transition:toView:] + 25
33  UIKit                               0x000000010f46f4d7 -[UINavigationController _startTransition:fromViewController:toViewController:] + 2893
34  UIKit                               0x000000010f46f787 -[UINavigationController _startDeferredTransitionIfNeeded:] + 547
35  UIKit                               0x000000010f470238 -[UINavigationController __viewWillLayoutSubviews] + 43
36  UIKit                               0x000000010f58a895 -[UILayoutContainerView layoutSubviews] + 202
37  UIKit                               0x000000010f3b7993 -[UIView(CALayerDelegate) layoutSublayersOfLayer:] + 354
38  QuartzCore                          0x000000011427c802 -[CALayer layoutSublayers] + 151
39  QuartzCore                          0x0000000114271369 _ZN2CA5Layer16layout_if_neededEPNS_11TransactionE + 363
40  QuartzCore                          0x00000001142711ea _ZN2CA5Layer28layout_and_display_if_neededEPNS_11TransactionE + 24
41  QuartzCore                          0x00000001141e4fb8 _ZN2CA7Context18commit_transactionEPNS_11TransactionE + 252
42  QuartzCore                          0x00000001141e6030 _ZN2CA11Transaction6commitEv + 394
43  QuartzCore                          0x00000001141e669d _ZN2CA11Transaction17observer_callbackEP19__CFRunLoopObservermPv + 89
44  CoreFoundation                      0x0000000110a27dc7 __CFRUNLOOP_IS_CALLING_OUT_TO_AN_OBSERVER_CALLBACK_FUNCTION__ + 23
45  CoreFoundation                      0x0000000110a27d37 __CFRunLoopDoObservers + 391
46  CoreFoundation                      0x0000000110a07522 __CFRunLoopRun + 946
47  CoreFoundation                      0x0000000110a06d83 CFRunLoopRunSpecific + 467
48  GraphicsServices                    0x0000000112dbdf04 GSEventRunModal + 161
49  UIKit                               0x000000010f357e33 UIApplicationMain + 1010
50  PSTappsperance                      0x000000010f092653 main + 115
51  libdyld.dylib                       0x00000001114b05fd start + 1
52  ???                                 0x0000000000000001 0x0 + 1
)libc++abi.dylib: terminating with uncaught exception of type NSException

Answer 1

This crash appears when you run your app with Margins and baselines in constraints on iOS 7.

To find and remove all dummy constraints strings you can do this:

Xcode doesn't highlight all these constraints correctly in Interface Builder, so you can use this solution:

1. Close Xcode
2. Open your storyboard file in your favorite text editor
3. Find all occurrences using the regex: (\w)Margin" and replace all of them with the pattern: \1" (the regex version is the one used in Sublime 2)
4. Find and remove from the storyboard file all the strings using the pattern: .*"baseline".*\n
5. Now save the file and open it in Xcode
6. Fix all appeared misaligns: find all warnings and press _"Update constraints for all views" to save the original position of all the views.
7. Profit!

---

Update: I found that "baseline" constraints causes crashes also, but Xcode doesn't show any warnings about these constrains!

Answer 2

Solved. It was because of Auto Layout constraints.

There were Labels that did not know to determine its width.

But why only works on iOS 8? I pinned two constraints to determine the width in Xcode 6

Trailing Space to: superview
Leading Space to: superview

when pinning constraints, there is an option 'Constraint to Margin', which is checked by default in Xcode 6. And Older versions does not support that.

Answer 3

You are right @Kyle. This is causing due to Auto Layout constraints. @Mazen, In my case too it was "First Baseline Alignment", removed it and worked. Here are some checks to detect/solve the problem.

1. To detect which storyboard causing this error you can perform a quick check. In "File Inspector", Uncheck the "Use Auto Layout" for the selected storyboard. Now, clean and build your application. If still getting the same error means the constraint causing this error is in another storyboard or in code.

2. Once you identify the storyboard, resolve the errors and warnings displayed by storyboard using Add Missing Constraints or other similar options.

3. To filter which constraint causing this error. Remove 3-4 constraints at a time(you can remove more to make it fast) to check if the error resolved. Once error resolved, identify the exact constraint which was causing this error.

4. Regarding "Constraint to Margin". In my case this is checked in few constraints but its not causing any error/warning below iOS8.

5. You can use this link to resolve auto layout issues. Resolving Auto Layout Issues

Hope this will help someone.