App crashing sometimes when transitioning between views: how to debug constraints? - ios

Question

I perform a transition between views with an animation. It sometimes works, and it also sometimes causes a crash and I don't understand why. I have my code within a #try-#catch block but no exception is retrieved in #catch. I simply get an app crash with a SIGABRT signal and the following log:
2015-09-23 10:03:43.420 My App[1510:528283] The view hierarchy is not prepared for the constraint:
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(UIConstraintBasedLayout) _viewHierarchyUnpreparedForConstraint:] to debug.
2015-09-23 10:03:43.421 My App[1510:528283] *** Assertion failure in -[UIView _layoutEngine_didAddLayoutConstraint:roundingAdjustment:mutuallyExclusiveConstraints:], /BuildRoot/Library/Caches/com.apple.xbs/Sources/UIKit/UIKit-3505.16/NSLayoutConstraint_UIKitAdditions.m:590
I don't understand why it sometimes works and other times it crashes, and I don't understand how can I debug this, please I need help.
Thanks in advance
EDIT:
This is the method that seems to cause the app crashes:
- (void)switchToMainView
{
[UIView transitionWithView:self.view
duration:1.0
options:UIViewAnimationOptionTransitionFlipFromRight
animations:^{
#try {
if ([self.secView superview]) {
[self setMainView];
[self.secView removeFromSuperview];
[self.view addSubview:self.mainView];
[self.view sendSubviewToBack:self.secView];
}
}
#catch (NSException *exception) {
NSLog(#"exception: %#", exception.description);
}
}
completion:^(BOOL finished){
if (finished) {
#try {
[self.view setNeedsUpdateConstraints];
[self setMessage];
}
#catch (NSException *exception) {
NSLog(#"exception: %#", exception.description);
}
}
}];
}
And the setMessage method that is called in the completion block:
- (void)setMessage
{
UIView *messageView = nil;
#try {
messageView = [[[NSBundle mainBundle] loadNibNamed:#"MessageView" owner:nil options:nil] firstObject];
messageView.frame = CGRectMake(0, 0, self.messagesContainerView.frame.size.width, self.messagesContainerView.frame.size.height);
[self.messagesContainerView.subviews makeObjectsPerformSelector: #selector(removeFromSuperview)];
[self.messagesContainerView addSubview:messageView];
}
#catch (NSException *exception) {
NSLog(#"exception: %#", exception.description);
}
}
where self.messagesContainerView is a subview of self.mainView in the first method.
Thanks again
EDIT 2:
This is the last crash information I managed to get:
Date/Time: 2015-09-24 10:01:13 +0000 OS Version: iPhone OS
9.0 (13A344) Report Version: 104
Exception Type: SIGABRT Exception Codes: #0 at 0x34de0d24 Crashed
Thread: 0
Application Specific Information:
*** Terminating app due to uncaught exception 'NSInternalInconsistencyException', reason: 'Impossible to set up
layout with view hierarchy unprepared for constraint.'
Last Exception Backtrace: 0 CoreFoundation
0x22ee786b 0x22df2000 + 1005675 1 libobjc.A.dylib
0x345e6dff 0x345e0000 + 28159 2 CoreFoundation
0x22ee7741 0x22df2000 + 1005377 3 Foundation
0x23c772ab 0x23be0000 + 619179 4 UIKit
0x277ced17 0x26fe7000 + 8289559 5 UIKit
0x270f8b1b 0x26fe7000 + 1121051 6 UIKit
0x270f898d 0x26fe7000 + 1120653 7 UIKit
0x270f88a7 0x26fe7000 + 1120423 8 UIKit
0x277cee6d 0x26fe7000 + 8289901 9 UIKit
0x270f878f 0x26fe7000 + 1120143 10 My App
0x000423c5 0x11000 + 201669 11 UIKit
0x277d479d 0x26fe7000 + 8312733 12 Foundation
0x23c29c81 0x23be0000 + 302209 13 UIKit
0x270fbaa9 0x26fe7000 + 1133225 14 UIKit
0x277d49d9 0x26fe7000 + 8313305 15 UIKit
0x270fc78b 0x26fe7000 + 1136523 16 Foundation
0x23c29c81 0x23be0000 + 302209 17 UIKit
0x270fbaa9 0x26fe7000 + 1133225 18 UIKit
0x270fc487 0x26fe7000 + 1135751 19 UIKit
0x277d4fa5 0x26fe7000 + 8314789 20 UIKit
0x272edfa9 0x26fe7000 + 3174313 21 UIKit
0x26ff56bb 0x26fe7000 + 59067 22 QuartzCore
0x268c167d 0x268b4000 + 54909 23 QuartzCore
0x268bcd79 0x268b4000 + 36217 24 QuartzCore
0x268bcc09 0x268b4000 + 35849 25 QuartzCore
0x268bc129 0x268b4000 + 33065 26 QuartzCore
0x268bbdeb 0x268b4000 + 32235 27 QuartzCore
0x268b55bf 0x268b4000 + 5567 28 CoreFoundation
0x22eaa0f1 0x22df2000 + 753905 29 CoreFoundation
0x22ea83e7 0x22df2000 + 746471 30 CoreFoundation
0x22ea8825 0x22df2000 + 747557 31 CoreFoundation
0x22dfb1e9 0x22df2000 + 37353 32 CoreFoundation
0x22dfafdd 0x22df2000 + 36829 33 GraphicsServices
0x2c09faf9 0x2c096000 + 39673 34 UIKit
0x2706018d 0x26fe7000 + 496013 35 My App
0x000d7d69 0x11000 + 814441 36 libdyld.dylib
0x34d11873 0x34d0f000 + 10355
Thread 0 Crashed: 0 libsystem_kernel.dylib 0x34de0d24
0x34dcc000 + 85284 1 libsystem_c.dylib 0x34d78f51
0x34d2e000 + 307025 2 My App 0x001abebf
0x11000 + 1683135 3 CoreFoundation 0x22ee7ba9
0x22df2000 + 1006505 4 libobjc.A.dylib
0x345e7087 0x345e0000 + 28807 5 libc++abi.dylib
0x33dcce17 0x33db6000 + 93719 6 libc++abi.dylib
0x33dcc8f7 0x33db6000 + 92407 7 libobjc.A.dylib
0x345e6f47 0x345e0000 + 28487 8 CoreFoundation
0x22dfb26f 0x22df2000 + 37487 9 CoreFoundation
0x22dfafdd 0x22df2000 + 36829 10 GraphicsServices
0x2c09faf9 0x2c096000 + 39673 11 UIKit
0x2706018d 0x26fe7000 + 496013 12 My App
0x000d7d69 0x11000 + 814441 13 libdyld.dylib
0x34d11873 0x34d0f000 + 10355

Answer 1

Without seeing your code It's hard to debug the actual problem. The probably causes are:
You are adding a constraint to a view that is not a superview of the constrained class.
You are adding a constraint to a view that has not been added as a subview yet - and so is not in the view hierarchy.
As to fixing it. I managed to create a project which crashes in this way, and correctly found the mistake by adding a symbolic breakpoint as the error suggests:
So try this and see where your problem is coming from.