ConstraintsMonitor

A tool to understand constraints warnings, only adding it as a dependency.

Without ConstraintsMonitor:

[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. 
	(Note: If you're seeing NSAutoresizingMaskLayoutConstraints that you don't understand, refer to the documentation for the UIView property translatesAutoresizingMaskIntoConstraints) 
(
    "<NSAutoresizingMaskLayoutConstraint:0x600003220d20 h=--& v=--& ConstraintsMonitor_Example.MyView:0x7fcdaff03e10.height == 896   (active)>",
    "<NSLayoutConstraint:0x600003220a50 UIView:0x7fcdaff031e0.height == 200   (active)>",
    "<NSLayoutConstraint:0x600003220410 V:|-(0)-[UIView:0x7fcdaff031e0]   (active, names: '|':ConstraintsMonitor_Example.MyView:0x7fcdaff03e10 )>",
    "<NSLayoutConstraint:0x600003220aa0 V:[UIView:0x7fcdaff031e0]-(0)-[UIView:0x7fcdaff03fc0]   (active)>",
    "<NSLayoutConstraint:0x600003220b90 UIView:0x7fcdaff03fc0.bottom == ConstraintsMonitor_Example.MyView:0x7fcdaff03e10.bottom   (active)>",
    "<NSLayoutConstraint:0x600003220be0 UIView:0x7fcdaff03fc0.height == 0.2*ConstraintsMonitor_Example.MyView:0x7fcdaff03e10.height   (active)>"
)

Will attempt to recover by breaking constraint 
<NSLayoutConstraint:0x600003220a50 UIView:0x7fcdaff031e0.height == 200   (active)>

With ConstraintsMonitor:

[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. 
	(Note: If you're seeing NSAutoresizingMaskLayoutConstraints that you don't understand, refer to the documentation for the UIView property translatesAutoresizingMaskIntoConstraints) 
(
    "UIViewControllerWrapperView.MyView.height == 896.0 (Did you set translatesAutoresizingMaskIntoConstraints = false?)",
    "MyView.UIView.height == 200.0 ",
    "MyView.UIView.top == UIViewControllerWrapperView.MyView.top (constant: 0.0)",
    "MyView.UIView.top == UIView.bottom (constant: 0.0)",
    "MyView.UIView.bottom == UIViewControllerWrapperView.MyView.bottom (constant: 0.0)",
    "MyView.UIView.height == UIViewControllerWrapperView.MyView.height (multiplier: 0.200)"
)

Will attempt to recover by breaking constraint 
MyView.UIView.height == 200.0 

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?

I was tired of looking for constraints issues and realizing what was really the issue, so I created this mini tool for printing nicer constraints

Installation

CocoaPods:

pod 'ConstraintsMonitor'

Swift Package Manager:

dependencies: [
  .package(url: "https://github.com/FranDepascuali/ConstraintsMonitor.git", from: "1.0.1")
]

Usage

Just by including this lib in your project, you will see nicer constraints warnings

Key Features

Use an identifier for the constraint if supplied.
Use the view identifier or the class name if the view is a subclass of UIView.
Show the parent view, so it's easier to know where to locate the issue.

How does it work?

By overriding the description property of the NSLayoutConstraint involved, we have a nicer way of viewing constraints.

Author

You can check my blog at https://deep-thought.netlify.com/ or @FranDepascuali in twitter.

License

ConstraintsMonitor is available under the MIT license. See the LICENSE file for more info.