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[LayoutConstraints] Unable to simultaneously satisfy constraints

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Lyn Tee
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[LayoutConstraints] 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. 
(
    "<NSLayoutConstraint:0x600000071d10 UIView:0x1555f3420.height >= 330   (active)>",
    "<NSLayoutConstraint:0x6000000733e0 V:|-(10)-[UILabel:0x1555f30f0]   (active, names: '|':UIView:0x1555f2f40 )>",
    "<NSLayoutConstraint:0x6000000734d0 V:[UILabel:0x1555f30f0]-(24)-[UIView:0x1555f3420]   (active)>",
    "<NSLayoutConstraint:0x600000073520 V:[UIView:0x1555f3420]-(16)-[UIPageControl:0x1555f35d0]   (active)>",
    "<NSLayoutConstraint:0x600000073610 V:[UIPageControl:0x1555f35d0]-(16)-|   (active, names: '|':UIView:0x1555f2f40 )>",
    "<NSLayoutConstraint:0x6000000737a0 V:|-(0)-[UIView:0x1555f2f40]   (active, names: '|':UITableViewCellContentView:0x1555ed190 )>",
    "<NSLayoutConstraint:0x6000000737f0 V:[UIView:0x1555f2f40]-(0)-|   (active, names: '|':UITableViewCellContentView:0x1555ed190 )>",
    "<NSLayoutConstraint:0x600000078460 'UIView-Encapsulated-Layout-Height' UITableViewCellContentView:0x1555ed190.height == 380   (active)>"
)

Will attempt to recover by breaking constraint 
<NSLayoutConstraint:0x600000071d10 UIView:0x1555f3420.height >= 330   (active)>

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

Why does this note appear? My code compiles fine.

  • It appears when Xcode realises there are multiple constraints on a view, and it can't fulfil all of them as instructed

  • Usually, the app compiles and runs fine. Even in the visual debugger, there is no issue

    • I assume this is because Xcode has already resolved the conflict at runtime, so that there no longer is a conflict when you open the visual debugger

How do I fix the conflicts?

Usually, you only need to fix ONE of the conflicts, not all.

  • Most scenarios resolve when you lower the priority of one of the constraints

  • The trick is in figuring out which one you need to lower

  • Once you figure that out, all the other constraint conflicts typically go away

This is how to read the conflicts:

  • V:|-(10)-[UILabel:0x1555f30f0]

    • V: this means Vertical

    • So this constraint means there is a UILabel with a padding of 10 between the top of the label and the topAnchor of its superview

    • 0x1555f30f0: Open the visual debugger, and then down the bottom, paste this into the filter. That will show you the correct UILabel

  • 'UIView-Encapsulated-Layout-Height' UITableViewCellContentView:0x1555ed190.height == 380

    • The view with conflicts uses a UITableView

    • Somewhere in your app, perhaps programmatically, the tableView.estimatedRowHeight has been set to 380

    • You should override this value to the correct number (which will be a larger number).

    • In the example above, Xcode has said the row height can be greater than 380, and that has fixed the issue.

When I've fixed the constraint, why does the note never go away?

When you see constraint conflicts like this, note that the debug console will only show ONE set of conflicting constraints at a time.

  • If you have a view with MULTIPLE constraint issues, the debugger will only complain about ONE. And it's always the same one.

  • Once you FIX this, the NEXT constraint conflict will appear

  • This can drive you mad if you don't realise the new conflict is totally different to the one you just fixed

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