如何在目标c中以编程方式添加约束 [英] How to add Constraint programmatically in objective c

问题描述

我想以编程方式添加约束，我使用下面的代码添加TOP和LEFT约束.

I want to add constraint programmatically and I use below code to add TOP and LEFT constraint.

NSLayoutConstraint *top = [NSLayoutConstraint constraintWithItem:label1
                                                       attribute:NSLayoutAttributeTop
                                                       relatedBy:NSLayoutRelationEqual
                                                          toItem:self.view
                                                       attribute:NSLayoutAttributeTop
                                                      multiplier:1
                                                        constant:110];


NSLayoutConstraint *left = [NSLayoutConstraint constraintWithItem:label1
                                                        attribute:NSLayoutAttributeLeading
                                                        relatedBy:NSLayoutRelationEqual
                                                           toItem:self.view
                                                        attribute:NSLayoutAttributeLeading
                                                       multiplier:1
                                                         constant:10];

lable1已添加到我的视图控制器中.当我在

lable1 is added in my view controller. When I add this two constraint in the view like

[self.view addConstraint:top];
[self.view addConstraint:left];

它给出了错误，约束不影响标签.

It gives the error in the consol and constraint does not affect the lable.

2016-02-09 19:36:59.824 testinMRC[99160:313382] 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:0x7fa5c8738610 V:|-(110)-[UILabel:0x7fa5c8626940'Label']   (Names: '|':UIView:0x7fa5c86267b0 )>",
    "<NSIBPrototypingLayoutConstraint:0x7fa5c8628a70 'IB auto generated at build time for view with fixed frame' V:|-(88)-[UILabel:0x7fa5c8626940'Label']   (Names: '|':UIView:0x7fa5c86267b0 )>"
)

Will attempt to recover by breaking constraint 
<NSLayoutConstraint:0x7fa5c8738610 V:|-(110)-[UILabel:0x7fa5c8626940'Label']   (Names: '|':UIView:0x7fa5c86267b0 )>

Make a symbolic breakpoint at UIViewAlertForUnsatisfiableConstraints to catch this in the debugger.
The methods in the UIConstraintBasedLayoutDebugging category on UIView listed in <UIKit/UIView.h> may also be helpful.
2016-02-09 19:36:59.889 testinMRC[99160:313382] 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:0x7fa5c87334b0 H:|-(10)-[UILabel:0x7fa5c8626940'Label']   (Names: '|':UIView:0x7fa5c86267b0 )>",
    "<NSIBPrototypingLayoutConstraint:0x7fa5c86285c0 'IB auto generated at build time for view with fixed frame' H:|-(188)-[UILabel:0x7fa5c8626940'Label'](LTR)   (Names: '|':UIView:0x7fa5c86267b0 )>"
)

Will attempt to recover by breaking constraint 
<NSLayoutConstraint:0x7fa5c87334b0 H:|-(10)-[UILabel:0x7fa5c8626940'Label']   (Names: '|':UIView:0x7fa5c86267b0 )>

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

有人可以告诉我为什么会出现此错误吗? 帮我缩短解决方案

Can anyone tell me why this error come? Help me to short out the solution

推荐答案

在您的情况下，错误明确指出您的视图约束冲突.可能是因为您尝试向Interface Builder中已包含约束的视图添加约束.即使您没有明确设置任何约束，IB也会在检测到某些约束缺失时为您提供约束.

In your case error clearly states that you have conflicting constraints for your view. Probably because you a trying to add constraints to the view that already has some from Interface Builder. Even if you didn't set up any constrains explicitly IB does provide them for you when it detects that some are missing.

在您提到的注释中，我看到您想以编程方式完成所有工作.在这种情况下，请看一段代码:

I see in comments you've mentioned that you want to do everything programmatically.In that case take a look at piece of code:

- (void)viewDidLoad {
    [super viewDidLoad];

    UIView *view = [UIView new];
    view.backgroundColor = [UIColor redColor];

    [view setTranslatesAutoresizingMaskIntoConstraints:NO];

    [self.view addSubview:view];

    NSLayoutConstraint *left = [NSLayoutConstraint constraintWithItem:view attribute:NSLayoutAttributeLeft relatedBy:NSLayoutRelationEqual toItem:self.view attribute:NSLayoutAttributeLeft multiplier:1 constant:100];
    NSLayoutConstraint *top = [NSLayoutConstraint constraintWithItem:view attribute:NSLayoutAttributeTop relatedBy:NSLayoutRelationEqual toItem:self.view attribute:NSLayoutAttributeTop multiplier:1 constant:100];

    NSLayoutConstraint *height = [NSLayoutConstraint constraintWithItem:view attribute:NSLayoutAttributeHeight relatedBy:NSLayoutRelationEqual toItem:nil attribute:NSLayoutAttributeNotAnAttribute multiplier:1 constant:50];
    NSLayoutConstraint *width = [NSLayoutConstraint constraintWithItem:view attribute:NSLayoutAttributeWidth relatedBy:NSLayoutRelationEqual toItem:nil attribute:NSLayoutAttributeNotAnAttribute multiplier:1 constant:50];

    [self.view addConstraints:@[left, top]];
    [view addConstraints:@[height, width]];

}

这很不言自明.如您所见，我必须在视图中添加宽度和高度约束，因为仅左和上并不能完全描述其位置.

It's pretty self-explanatory. As you can see I had to add width and height constraints to the view, because only left and top doesn't fully describe it's position.

结果:

我鼓励您尝试使用Visual Format Language.用更少的代码可以达到相同的结果.这段代码导致了完全相同的结果:

I encourage you to try out Visual Format Language. Same result can be achieved with much less code. This code leads to the very same result:

NSArray *horizontal = [NSLayoutConstraint constraintsWithVisualFormat:@"|-100-[view(50)]" options:0 metrics:nil views:@{@"view" : view}];
NSArray *vertical = [NSLayoutConstraint constraintsWithVisualFormat:@"V:|-100-[view(50)]" options:0 metrics:nil views:@{@"view" : view}];

[self.view addConstraints:vertical];
[self.view addConstraints:horizontal];

让我知道这是否有帮助.干杯.

Let me know if this helped. Cheers.

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