CODEWITHSUNDEEP
iosobjective-cuitableviewautolayoutnslayoutconstraint
JamEngulfer
JamEngulfer

Reputation: 747

NSLayoutConstraint errors only when switching view controllers

I'm getting some very weird behaviour from one of my view controllers.

I'm navigating to the same controller (with different instances of it) from two different UITableViews in different tabs.

When it gets displayed from a tap on a UITableViewCell, everything is fine and no errors display. If I have the controller open and I navigate away from it by selecting another tab, then navigating back to it through pressing the original tab, I get a large amount of NSLayoutConstraint errors.

I don't actually have any constraints in my cell and I don't have any UI elements on the cell's content view in the Storyboard, as I'm adding all of them programmatically. I'm not defining any constraints in the code either.

The full error is here, as it's too large to reasonably paste into SO.

An excerpt is as follows:

2015-04-11 16:49:23.889 TradingPost[6982:60b] Unable to simultaneously satisfy constraints.
Probably at least one of the constraints in the following list is one you don't want. Try this: (1) look at each constraint and try to figure out which you don't expect; (2) find the code that added the unwanted constraint or constraints and fix it. (Note: If you're seeing NSAutoresizingMaskLayoutConstraints that you don't understand, refer to the documentation for the UIView property translatesAutoresizingMaskIntoConstraints) 
(
"<NSLayoutConstraint:0x155e5250 H:[UILabel:0x155d8150(158)]>",
"<NSLayoutConstraint:0x155ed9e0 H:|-(8)-[UILabel:0x155d8150]   (Names: '|':UITableViewCellContentView:0x155d4a80 )>",
"<NSLayoutConstraint:0x155eda30 H:[UILabel:0x155d8150]-(47)-[UIView:0x155e01a0]>",
"<NSLayoutConstraint:0x155f1bc0 UIView:0x155e01a0.trailing == UITableViewCellContentView:0x155d4a80.trailing - 8>",
"<NSAutoresizingMaskLayoutConstraint:0x156b7640 h=--& v=--& H:[UITableViewCellContentView:0x155d4a80(0)]>"
)

Will attempt to recover by breaking constraint 
<NSLayoutConstraint:0x155e5250 H:[UILabel:0x155d8150(158)]>

Break on objc_exception_throw to catch this in the debugger.
The methods in the UIConstraintBasedLayoutDebugging category on UIView listed in <UIKit/UIView.h> may also be helpful.

Addition: Upon further investigation, I find I'm still getting errors, even when I remove all UI generating code from the controller and all constraints from the Storyboard. At this point I'm suspecting witchcraft.

Upvotes: 0

Views: 59

Answers (2)

JamEngulfer
JamEngulfer

Reputation: 747

I found that another view, attached to the one that I thought was causing the trouble, was the actual cause of the problem.

All it needed was a reset of the constraints to fix it, I just completely forgot about it when I encountered this problem.

Upvotes: 0

Caleb
Caleb

Reputation: 124997

Even if you don't create any constraints explicitly, the auto layout system can create them from the autoresizingMask mask associated with each view. You can try setting translatesAutoresizingMaskIntoConstraints to NO. However, if you're using auto layout and size classes to create an interface that adapts to various screen sizes, you'll probably need to embrace constraints. In that case, you might be better off setting the relevant constraints explicitly in your code.

Upvotes: 2

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