ios - UIStackView "Unable to simultaneously satisfy constraints" on "squished" hidden views

Question

When my UIStackView "rows" are squished, they throw AutoLayout warnings. However, they display fine and nothing else is wrong besides these sorts of loggings:

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) (

So, I'm not sure how to fix this yet, but it doesn't seem to break anything besides just being annoying.

Does anyone know how to solve it? Interestingly, the layout constraints are tagged quite often with 'UISV-hiding', indicating that perhaps it should ignore the height minimums for subviews or something in this instance?

Answer 1

You get this issue because when setting a subview from within UIStackView to hidden, it will first constrain its height to zero in order to animate it out.

I was getting the following error:

2015-10-01 11:45:13.732 <redacted>[64455:6368084] 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:0x7f7f5be18c80 V:[UISegmentedControl:0x7f7f5bec4180]-(8)-|   (Names: '|':UIView:0x7f7f5be69d30 )>",
    "<NSLayoutConstraint:0x7f7f5be508d0 V:|-(8)-[UISegmentedControl:0x7f7f5bec4180]   (Names: '|':UIView:0x7f7f5be69d30 )>",
    "<NSLayoutConstraint:0x7f7f5bdfbda0 'UISV-hiding' V:[UIView:0x7f7f5be69d30(0)]>"
)

Will attempt to recover by breaking constraint 
<NSLayoutConstraint:0x7f7f5be18c80 V:[UISegmentedControl:0x7f7f5bec4180]-(8)-|   (Names: '|':UIView:0x7f7f5be69d30 )>

Make a symbolic breakpoint at UIViewAlertForUnsatisfiableConstraints to catch this in the debugger.
The methods in the UIConstraintBasedLayoutDebugging category on UIView listed in <UIKit/UIView.h> may also be helpful.

What I was trying to do, was to place a UIView within my UIStackView that contained a UISegmentedControl inset by 8pts on each edge.

When I set it to hidden, it would try to constrain the container view to a zero height but because i have a set of constraints from top to bottom, there was a conflict.

To resolve the issue, I changed my 8pt top an bottom constraints priority from 1000 to 999 so the UISV-hiding constraint can then take priority if needed.