ios - AutoLayout, Unable to simultaneously satisfy constraints

Question

Just started learning iOS AutoLayout, Interface builder very straight forward, but when I try to archive the same thing on the code

    [self.view addConstraints:[NSLayoutConstraint constraintsWithVisualFormat:@"H:|-(==2)-[_nextKeyboardButton]-(==2)-[_numPadButton]-(==2)-[_spaceButton]-(==2)-[_returnButton]-(==2)-|" options:0 metrics:0 views:NSDictionaryOfVariableBindings(_nextKeyboardButton,_numPadButton,_spaceButton,_returnButton)]];

it raises an exception,

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:0x6000000966c0 H:|-(2)-[UIButton:0x7fe4f1d1c760'Next']   (Names: '|':UIInputView:0x7fe4f1f04d00 )>",
 "<NSLayoutConstraint:0x600000096710 H:[UIButton:0x7fe4f1d1c760'Next']-(2)-[UIButton:0x7fe4f1d1d1d0'123']>",
 "<NSLayoutConstraint:0x600000096760 H:[UIButton:0x7fe4f1d1d1d0'123']-(2)-[UIButton:0x7fe4f1d1d6f0'Space']>",
 "<NSLayoutConstraint:0x6000000967b0 H:[UIButton:0x7fe4f1d1d6f0'Space']-(2)-[UIButton:0x7fe4f1d1d8d0'Return']>",
 "<NSLayoutConstraint:0x600000096800 H:[UIButton:0x7fe4f1d1d8d0'Return']-(2)-|   (Names: '|':UIInputView:0x7fe4f1f04d00 )>",
 "<NSLayoutConstraint:0x600000096e40 'UIView-Encapsulated-Layout-Width' H:[UIInputView:0x7fe4f1f04d00(0)]>"
 )

Will attempt to recover by breaking constraint
<NSLayoutConstraint:0x6000000967b0 H:[UIButton:0x7fe4f1d1d6f0'Space']-(2)-[UIButton:0x7fe4f1d1d8d0'Return']>

All 4 buttons .translatesAutoresizingMaskIntoConstraints = NO;

I wonder what is wrong ? help is really appreciated :)

FYI: I work on iOS8 SDK

Answer 1

The easiest way how to find unsatisfiable constraints:

• set unique identifier for every constraint in your view:

• create simple extension for NSLayoutConstraint:

SWIFT:

extension NSLayoutConstraint {

    override public var description: String {
        let id = identifier ?? ""
        return "id: (id), constant: (constant)" //you may print whatever you want here
    }
}

OBJECTIVE-C

@interface NSLayoutConstraint (Description)

@end

@implementation NSLayoutConstraint (Description)

-(NSString *)description {
    return [NSString stringWithFormat:@"id: %@, constant: %f", self.identifier, self.constant];
}

@end

• build it once again, and now you have more readable output for you:

• once you got your id you can simple tap it in your Find Navigator:

• and quickly find it:

HOW TO SIMPLE FIX THAT CASE?

• try to change priority to 999 for broken constraint.

See the related answer here: Unable to simultaneously satisfy constraints, will attempt to recover by breaking constraint