app crash

2015-01-17 17:42:48.391 trash[4034:504194] The view hierarchy is not prepared for the constraint: <NSLayoutConstraint:0x7fb24d815a40 UIView:0x7fb24b7077e0.right == UIScrollView:0x7fb24b7092a0.right>
	When added to a view, the constraint's items must be descendants of that view (or the view itself). This will crash if the constraint needs to be resolved before the view hierarchy is assembled. Break on -[UIView _viewHierarchyUnpreparedForConstraint:] to debug.
2015-01-17 17:42:48.392 trash[4034:504194] *** Assertion failure in -[UIView _layoutEngine_didAddLayoutConstraint:roundingAdjustment:mutuallyExclusiveConstraints:], /SourceCache/UIKit_Sim/UIKit-3318.16.14/NSLayoutConstraint_UIKitAdditions.m:560
2015-01-17 17:42:48.394 trash[4034:504194] *** Terminating app due to uncaught exception 'NSInternalInconsistencyException', reason: 'Impossible to set up layout with view hierarchy unprepared for constraint.'
*** First throw call stack:
(
	0   CoreFoundation                      0x000000010e53cf35 __exceptionPreprocess + 165
	1   libobjc.A.dylib                     0x000000010e1d5bb7 objc_exception_throw + 45
	2   CoreFoundation                      0x000000010e53cd9a +[NSException raise:format:arguments:] + 106
	3   Foundation                          0x000000010ddf25df -[NSAssertionHandler handleFailureInMethod:object:file:lineNumber:description:] + 195
	4   UIKit                               0x000000010efa3cf2 __120-[UIView(UIConstraintBasedLayout) _layoutEngine_didAddLayoutConstraint:roundingAdjustment:mutuallyExclusiveConstraints:]_block_invoke_2 + 177
	5   UIKit                               0x000000010efa3bf0 -[UIView(UIConstraintBasedLayout) _layoutEngine_didAddLayoutConstraint:roundingAdjustment:mutuallyExclusiveConstraints:] + 386
	6   UIKit                               0x000000010efa3ea4 -[UIView(UIConstraintBasedLayout) _tryToAddConstraintWithoutUpdatingConstraintsArray:roundingAdjustment:mutuallyExclusiveConstraints:] + 30
	7   UIKit                               0x000000010efa3fcc -[UIView(UIConstraintBasedLayout) _tryToAddConstraint:roundingAdjustment:mutuallyExclusiveConstraints:] + 243
	8   UIKit                               0x000000010efa430b __50-[UIView(UIConstraintBasedLayout) addConstraints:]_block_invoke + 188
	9   Foundation                          0x000000010dd7bd6e -[NSISEngine withBehaviors:performModifications:] + 155
	10  UIKit                               0x000000010efa4240 -[UIView(UIConstraintBasedLayout) addConstraints:] + 263
	11  trash                               0x000000010dca7ac0 -[ViewController viewDidLoad] + 1616
	12  UIKit                               0x000000010ea4ea90 -[UIViewController loadViewIfRequired] + 738
	13  UIKit                               0x000000010ea4ec8e -[UIViewController view] + 27
	14  UIKit                               0x000000010e96dca9 -[UIWindow addRootViewControllerViewIfPossible] + 58
	15  UIKit                               0x000000010e96e041 -[UIWindow _setHidden:forced:] + 247
	16  UIKit                               0x000000010e97a72c -[UIWindow makeKeyAndVisible] + 42
	17  UIKit                               0x000000010e925061 -[UIApplication _callInitializationDelegatesForMainScene:transitionContext:] + 2628
	18  UIKit                               0x000000010e927d2c -[UIApplication _runWithMainScene:transitionContext:completion:] + 1350
	19  UIKit                               0x000000010e926bf2 -[UIApplication workspaceDidEndTransaction:] + 179
	20  FrontBoardServices                  0x00000001110e52a3 __31-[FBSSerialQueue performAsync:]_block_invoke + 16
	21  CoreFoundation                      0x000000010e47253c __CFRUNLOOP_IS_CALLING_OUT_TO_A_BLOCK__ + 12
	22  CoreFoundation                      0x000000010e468285 __CFRunLoopDoBlocks + 341
	23  CoreFoundation                      0x000000010e468045 __CFRunLoopRun + 2389
	24  CoreFoundation                      0x000000010e467486 CFRunLoopRunSpecific + 470
	25  UIKit                               0x000000010e926669 -[UIApplication _run] + 413
	26  UIKit                               0x000000010e929420 UIApplicationMain + 1282
	27  trash                               0x000000010dca88a3 main + 115
	28  libdyld.dylib                       0x0000000110acc145 start + 1
	29  ???                                 0x0000000000000001 0x0 + 1
)
libc++abi.dylib: terminating with uncaught exception of type NSException
(lldb)