AutoLayout自动布局,NSLayoutConstraint 视图约束使用

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

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

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

 #import "ViewController.h"

 @interface ViewController ()

 @end

 @implementation ViewController

 - (void)viewDidLoad {
     [super viewDidLoad];
     //创建添加blueview
     UIView *blueView=[[UIView alloc] init];
     blueView.backgroundColor = [UIColor blueColor];
     blueView.translatesAutoresizingMaskIntoConstraints = NO;//禁止Autoresizing
     [self.view addSubview:blueView];

     //创建添加redView
     UIView *redView=[[UIView alloc] init];
     redView.backgroundColor = [UIColor redColor];
     redView.translatesAutoresizingMaskIntoConstraints = NO;
     [self.view addSubview:redView];

     // 1.0父View左边 约束 blueView左边 30
     NSLayoutConstraint *blueLeftCon=[NSLayoutConstraint constraintWithItem:blueView attribute:NSLayoutAttributeLeft relatedBy:NSLayoutRelationEqual toItem:self.view attribute:NSLayoutAttributeLeft multiplier:1.0 constant:30.0];
     [self.view addConstraint:blueLeftCon];

     // 1.1父View顶部 约束 blueView顶部 30
     NSLayoutConstraint *blueTopCon=[NSLayoutConstraint constraintWithItem:blueView attribute:NSLayoutAttributeTop relatedBy:NSLayoutRelationEqual toItem:self.view attribute:NSLayoutAttributeTop multiplier:1.0 constant:30.0 ];
     [self.view addConstraint:blueTopCon];

      // 1.2父View右边 约束 blueView右边 30
     NSLayoutConstraint *blueRightCon= [NSLayoutConstraint constraintWithItem:blueView attribute:NSLayoutAttributeRight relatedBy:NSLayoutRelationEqual toItem:self.view attribute:NSLayoutAttributeRight multiplier:1.0 constant:- ];
     [self.view addConstraint:blueRightCon];

     // 1.3 blueView 相当于 高度设置成50
     NSLayoutConstraint *blueHeightCon=[NSLayoutConstraint constraintWithItem:blueView attribute:NSLayoutAttributeHeight relatedBy:NSLayoutRelationEqual toItem:nil attribute: multiplier: constant:];
     [blueView addConstraint:blueHeightCon];

     //2.0 redView 顶部 和 blueView 底部 间距20
     NSLayoutConstraint *redTopCon=[NSLayoutConstraint constraintWithItem:redView attribute:NSLayoutAttributeTop relatedBy:NSLayoutRelationEqual toItem:blueView attribute:NSLayoutAttributeBottom multiplier:1.0 constant:];
     [self.view addConstraint:redTopCon];

     //2.1 redView 左边 和 blueView 水平中心线对齐
     NSLayoutConstraint *redLeftCon=[NSLayoutConstraint constraintWithItem:redView attribute:NSLayoutAttributeLeft relatedBy:NSLayoutRelationEqual   toItem:blueView attribute:NSLayoutAttributeCenterX multiplier:1.0 constant:];
     [self.view addConstraint:redLeftCon];

     //2.2 redView 右边 参照 blueView 右边对齐
     NSLayoutConstraint *redRightCon = [NSLayoutConstraint constraintWithItem:redView attribute:NSLayoutAttributeRight relatedBy:NSLayoutRelationEqual toItem:blueView attribute:NSLayoutAttributeRight multiplier:1.0 constant:];
     [self.view addConstraint:redRightCon];

     //2.3 redView 高度 参照 blueView 高度相等
     NSLayoutConstraint *redHeightCon=[NSLayoutConstraint constraintWithItem:redView attribute:NSLayoutAttributeHeight relatedBy:NSLayoutRelationEqual toItem:blueView attribute:NSLayoutAttributeHeight multiplier:1.0 constant:];
     [self.view addConstraint:redHeightCon];

 }

 @end

2.storyboard实现：

效果：