一.方法
NSLayoutConstraint *constraint = [NSLayoutConstraint constraintWithItem:<#(id)#> attribute:<#(NSLayoutAttribute)#> relatedBy:<#(NSLayoutRelation)#> toItem:<#(id)#> attribute:<#(NSLayoutAttribute)#> multiplier:<#(CGFloat)#> constant:<#(CGFloat)#>]
Item:要约束的控件
attribute:要约束的控件约束的类型(做怎样的约束)
relatedBy:与参照控件之间的关系
toItem:参照的控件
attribute:参照的控件约束的类型(做怎样的约束)
multiplier:约束的控件和参照的控件关系倍数
constant:常量
最后两个参数计算关系:
view1.property1 =(view2.property2 * multiplier)+ constant
二.Autolayout的常见警告和错误
1.警告![](https://images0.cnblogs.com/blog2015/490811/201508/230009386283276.png)
![](https://images0.cnblogs.com/blog2015/490811/201508/230009386283276.png)
控件的frame不匹配所添加的约束, 比如:约束控件的宽度为150, 而控件现在的宽度是160
2.错误![](https://images0.cnblogs.com/blog2015/490811/201508/230009523315129.png)
![](https://images0.cnblogs.com/blog2015/490811/201508/230009523315129.png)
缺乏必要的约束, 比如:只约束了宽度和高度, 没有约束具体的位置
两个约束冲突,比如:1个约束控件的宽度为150, 1个约束控件的宽度为160
三.例子
1.代码实现:
ViewController.m
![](https://images.cnblogs.com/OutliningIndicators/ContractedBlock.gif)
1 #import "ViewController.h" 2 3 @interface ViewController () 4 5 @end 6 7 @implementation ViewController 8 9 - (void)viewDidLoad { 10 [super viewDidLoad]; 11 //创建添加blueview 12 UIView *blueView=[[UIView alloc] init]; 13 blueView.backgroundColor = [UIColor blueColor]; 14 blueView.translatesAutoresizingMaskIntoConstraints = NO;//禁止Autoresizing 15 [self.view addSubview:blueView]; 16 17 //创建添加redView 18 UIView *redView=[[UIView alloc] init]; 19 redView.backgroundColor = [UIColor redColor]; 20 redView.translatesAutoresizingMaskIntoConstraints = NO; 21 [self.view addSubview:redView]; 22 23 // 1.0父View左边 约束 blueView左边 30 24 NSLayoutConstraint *blueLeftCon=[NSLayoutConstraint constraintWithItem:blueView attribute:NSLayoutAttributeLeft relatedBy:NSLayoutRelationEqual toItem:self.view attribute:NSLayoutAttributeLeft multiplier:1.0 constant:30.0]; 25 [self.view addConstraint:blueLeftCon]; 26 27 // 1.1父View顶部 约束 blueView顶部 30 28 NSLayoutConstraint *blueTopCon=[NSLayoutConstraint constraintWithItem:blueView attribute:NSLayoutAttributeTop relatedBy:NSLayoutRelationEqual toItem:self.view attribute:NSLayoutAttributeTop multiplier:1.0 constant:30.0 ]; 29 [self.view addConstraint:blueTopCon]; 30 31 // 1.2父View右边 约束 blueView右边 30 32 NSLayoutConstraint *blueRightCon= [NSLayoutConstraint constraintWithItem:blueView attribute:NSLayoutAttributeRight relatedBy:NSLayoutRelationEqual toItem:self.view attribute:NSLayoutAttributeRight multiplier:1.0 constant:-30 ]; 33 [self.view addConstraint:blueRightCon]; 34 35 // 1.3 blueView 相当于 高度设置成50 36 NSLayoutConstraint *blueHeightCon=[NSLayoutConstraint constraintWithItem:blueView attribute:NSLayoutAttributeHeight relatedBy:NSLayoutRelationEqual toItem:nil attribute:0 multiplier:0 constant:50]; 37 [blueView addConstraint:blueHeightCon]; 38 39 //2.0 redView 顶部 和 blueView 底部 间距20 40 NSLayoutConstraint *redTopCon=[NSLayoutConstraint constraintWithItem:redView attribute:NSLayoutAttributeTop relatedBy:NSLayoutRelationEqual toItem:blueView attribute:NSLayoutAttributeBottom multiplier:1.0 constant:20]; 41 [self.view addConstraint:redTopCon]; 42 43 //2.1 redView 左边 和 blueView 水平中心线对齐 44 NSLayoutConstraint *redLeftCon=[NSLayoutConstraint constraintWithItem:redView attribute:NSLayoutAttributeLeft relatedBy:NSLayoutRelationEqual toItem:blueView attribute:NSLayoutAttributeCenterX multiplier:1.0 constant:0]; 45 [self.view addConstraint:redLeftCon]; 46 47 //2.2 redView 右边 参照 blueView 右边对齐 48 NSLayoutConstraint *redRightCon = [NSLayoutConstraint constraintWithItem:redView attribute:NSLayoutAttributeRight relatedBy:NSLayoutRelationEqual toItem:blueView attribute:NSLayoutAttributeRight multiplier:1.0 constant:0]; 49 [self.view addConstraint:redRightCon]; 50 51 //2.3 redView 高度 参照 blueView 高度相等 52 NSLayoutConstraint *redHeightCon=[NSLayoutConstraint constraintWithItem:redView attribute:NSLayoutAttributeHeight relatedBy:NSLayoutRelationEqual toItem:blueView attribute:NSLayoutAttributeHeight multiplier:1.0 constant:0]; 53 [self.view addConstraint:redHeightCon]; 54 55 } 56 57 @end
2.storyboard实现:
效果: