禁用自动版式时，“无法同时满足约束条件”

Question

I have disabled Auto Layout in the interface builder for a specific view:

But I get this error in the console, when I load the ViewController for the xib file:

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)

I am working with frames in this view and I usually don't get any Auto Layout errors when I have disabled it in the Interface Builder. This is the constraints that seems to break:

(
    "<NSLayoutConstraint:0x170f5cd0 V:[UIView:0x1709e560]-(0)-[UITableView:0x162e2200]>",
    "<NSAutoresizingMaskLayoutConstraint:0x17185130 h=--& v=--& UIView:0x1709e560.midY == + 48>",
    "<NSAutoresizingMaskLayoutConstraint:0x157e29a0 h=--& v=--& V:[UIView:0x1709e560(96)]>",
    "<NSAutoresizingMaskLayoutConstraint:0x171c2670 h=--& v=--& TableHeaderView:0x1705d1c0.midY == + 72.5>",
    "<NSAutoresizingMaskLayoutConstraint:0x171cb510 h=--& v=--& V:[TableHeaderView:0x1705d1c0(145)]>",
    "<NSAutoresizingMaskLayoutConstraint:0x1573fca0 h=-&- v=-&- UITableView:0x162e2200.midY == UIView:0x17505080.midY + 72.5>",
    "<NSAutoresizingMaskLayoutConstraint:0x1573fcd0 h=-&- v=-&- UITableView:0x162e2200.height == UIView:0x17505080.height - 145>",
    "<NSAutoresizingMaskLayoutConstraint:0x171e4450 h=-&- v=-&- 'UIView-Encapsulated-Layout-Top' V:|-(0)-[UIView:0x17505080]   (Names: '|':UIViewControllerWrapperView:0x17034d00 )>"
)

Will attempt to recover by breaking constraint 
<NSLayoutConstraint:0x16c9ad30 V:[UIView:0x16cc2a00]-(0)-[UITableView:0x15249400]>

Correct me if I am wrong, but I only thought I would be getting this error if Auto Layout was enabled?

To me it seems like it thinks I have setup a constraint between the UIView and the UITableView , but I havn't! Auto Layout is disabled in the Interface Builder and I do not set any constraints in the code.

I have tried setting translatesAutoresizingMaskIntoConstraints to NO , but my frames are not respected when I do this.

It seems to me, like the view is working with Auto Layout. I have tried to delete the file and construct it again, but I still get the same error.

Why am I getting this error when Auto Layout is disabled in the xib file?

EDIT:

It turns out that I had made a mistake when I was searching for constraints. I found this line in my code:

NSDictionary* views = @{@"searchHeaderView": self.searchHeader.view, @"tableView": self.tableView};
[self.view addConstraints:[NSLayoutConstraint constraintsWithVisualFormat:@"V:[searchHeaderView]-(==0)-[tableView]" options:0 metrics:nil views:views]];

I think that explains it :-P

Answer 1

Something weird is going on, because if you look closely, the memory addresses of at the 'will break' constraint and views attached to it are not in the array, so these are different instances.

Regardless, the unwelcome Auto Layout behavior is consistent with your suspicion: If one constraint gets added to the view hierarchy, AutoLayout "turns back on" at least for for that part of it and you get a mess of autoresizingmask constraints.

So this is a debugging issue. Some commands methods you can use in the debugger:

po [[UIWindow keyWindow] recursiveDescription]

Gives you a complete outline of the view hierarchy, with UIView descriptions, which include frames.

po [[UIWindow keyWindow] _autolayoutTrace]

This is private API but that's not an issue during development and especially not debugging. This actually works best if you follow the suggestion and add a symbolic breakpoint at UIViewAlertForUnsatisfiableConstraints (the breakpoints navigator, at the bottom). Best of luck.

Answer 2

I am pretty sure that if you do not want to use AutoLayout then you need to set translatesAutoresizingMaskIntoConstraints to YES rather than NO .

This then ensures that constraints are created for you which reflect the position drawn in interface builder without you having to add constraints. Perhaps you have some constraints assigned which clash with those it thinks it needs to autogenerate? I would remove any constraints, if you can find any. If there are none to delete, can you post the list it says are clashing?