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.