AutoLayout，无法同时满足约束

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

Answer 2

I had to struggle with similar problem when I was trying to manually create all the auto layout constraints (in Swift, using Snappy - a Masonry port to Swift) in a view controller that is based on a Storyboard.

For some reason, Xcode generates own default set of auto layout constraints on a NIB at build time. This is why I couldn't add any more manual constraints, because they were conflicting with the automatically added ones.

I resolved this the following way:

• Open up the Storyboard view controller you're handling.

• Select the view controller and select Editor > Resolve Auto Layout Issues > All Views in [ ] View Controller > Add Missing Constraints from the menu:

(This will ensure that no additional build time constraints are created and all the constraints are now visible.)

• Select all the constraints from your view controller:

• Check from the right pane the following check box: Placeholder - Remove at build time :

Now you can add all the auto layout constraints manually in the code.

Answer 3

It may be not so difficult.The message console output says that the UIButton's constraints redefined.It means just like that you put a constraint that restrict the Height and the Width of the button, but needlessly you put another restriction that the button has a Aspect Ratio .In this condition Xcode can't make sure which constraint to follow,so that you can see this debug message in console.

There are two ways Useful for me:

1. Analyse the constraints displayed in the console,and try to delete one or more constraint.

2.If you are using the storyboard or Xib ,Select a constraint ->Show the Attributes Inspector -> change the priority of some Constraints.

---

One more thing...

You can follow the article of Jason Jarrett. Add a symbol breakpoint to make sure which view make the error happen.

Answer 4

In case anyone else runs into this, an easy way to visually check for problems with your constraints is this site (it's really useful!):

http://www.wtfautolayout.com

Here's the Github project in case the site goes down: https://github.com/johnpatrickmorgan/wtfautolayout

Answer 5

According to your question what i've understood that you have created control in nib and you are directly trying to change is constraints from your class.

What you can do here is set constraints in nib for view controller and then bind it with your class and use objects of constraints. Or you can create view programmatically and directly set the constraints.

// You also need to check that whether you need to “translatesAutoresizingMaskIntoConstraints” if “YES - the view's superview looks at the view's autoresizing mask, produces constraints that implement it, and adds those constraints to itself (the superview).” and if “NO - the view's superview does not looks at the view's autoresizing mask, and not produces constraints that implement it.”

I also got same issue and I fixed it as following

     [_nextKeyboardButton setTranslatesAutoresizingMaskIntoConstraints:YES];
    _numPadButton.translatesAutoresizingMaskIntoConstraints = YES;
    [_numPadButton updateConstraints];
    [_nextKeyboardButton updateConstraints];

    NSArray *constraints2 = [NSLayoutConstraint
                             constraintsWithVisualFormat:@"H:|-57-[_nextKeyboardButton(96)]"
                             options:0
                             metrics:nil
                             views:NSDictionaryOfVariableBindings(_nextKeyboardButton)];

    [self.view addConstraints:constraints2];

    NSArray *constraints4 = [NSLayoutConstraint
                             constraintsWithVisualFormat:@"V:|-123-[_nextKeyboardButton(30)]"
                             options:0
                             metrics:nil
                             views:NSDictionaryOfVariableBindings(_nextKeyboardButton)];

    [self.view addConstraints:constraints4];

    NSArray *constraints1 = [NSLayoutConstraint
                             constraintsWithVisualFormat:@"H:|-207-[_numPadButton(58)]"
                             options:0
                             metrics:nil
                             views:NSDictionaryOfVariableBindings(_numPadButton)];

    [self.view addConstraints:constraints1];

    NSArray *constraints3 = [NSLayoutConstraint
                             constraintsWithVisualFormat:@"V:|-123-[_numPadButton(30)]"
                             options:0
                             metrics:nil
                             views:NSDictionaryOfVariableBindings(_numPadButton)];

    [self.view addConstraints:constraints3];

// Create Controls  or view programmatically.

UILabel *label = [UILabel new];
    label.text = @"This is a Label";
    label.font = [UIFont systemFontOfSize:18];
    label.backgroundColor = [UIColor lightGrayColor];
    label.translatesAutoresizingMaskIntoConstraints = NO;
    [self.view addSubview:label];

    NSArray *constraints = [NSLayoutConstraint
                            constraintsWithVisualFormat:@"V:|-offsetTop-[label(100)]"
                            options:0
                            metrics:@{@"offsetTop": @100}
                            views:NSDictionaryOfVariableBindings(label)];
    [self.view addConstraints:constraints];

    UIView *spacer1 = [UIView new];
    spacer1.translatesAutoresizingMaskIntoConstraints = NO;
    [spacer1 setBackgroundColor:[UIColor redColor]];
    [self.view addSubview:spacer1];

    UIView *spacer2 = [UIView new];
    spacer2.translatesAutoresizingMaskIntoConstraints = NO;
    [spacer2 setBackgroundColor:[UIColor greenColor]];
    [self.view addSubview:spacer2];

    NSArray *constraints1 = [NSLayoutConstraint
                            constraintsWithVisualFormat:@"V:|-offsetTop-[spacer1(100)]"
                            options:0
                            metrics:@{@"offsetTop": @100}
                            views:NSDictionaryOfVariableBindings(spacer1)];

    [self.view addConstraints:constraints1];

    NSArray *constraints2 = [NSLayoutConstraint
                             constraintsWithVisualFormat:@"V:|-offsetTop-[spacer2(100)]"
                             options:0
                             metrics:@{@"offsetTop": @100}
                             views:NSDictionaryOfVariableBindings(spacer2)];

    [self.view addConstraints:constraints2];

    [self.view addConstraints:[NSLayoutConstraint
                               constraintsWithVisualFormat:@"H:|[spacer1]-10-[label]-20-[spacer2(==spacer1)]|"
                               options:0
                               metrics:nil
                               views:NSDictionaryOfVariableBindings(label, spacer1, spacer2)]];

So when using AutoLayout, you should never directly set the frame of a view. Constraints are used to do this for you. Normally if you want to set your own constraints in a view, you should override the updateConstraintsmethod of your UIViews. Make sure the content views for the page controller allow for their edges to be resized since they will be sized to fit the page view's frame. Your constraints and view setup will need to account for this, or you you will get unsatisfiable constraint errors.

https://developer.apple.com/library/mac/documentation/userexperience/conceptual/AutolayoutPG/AutoLayoutConcepts/AutoLayoutConcepts.html#//apple_ref/doc/uid/TP40010853-CH14-SW1 You can also refer above link of apple to in-depth study and if you still face issue i'll be try my level best to solve you issue.

Answer 6

我用 NSLayoutConstraint.deactivate(MystackView.constraints) 解决了我的问题