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
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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
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blueview12 UIView *blueView=[[UIView alloc] init];13 blueView.backgroundColor = [UIColor blueColor];14 blueView.translatesAutoresizingMaskIntoConstraints = NO;//禁止Autoresizing15 [self.view addSubview:blueView];16 17 //创建添加redView18 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 3024 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 3028 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 3032 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5036 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2040 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
View Code
2.storyboard实现:
效果:
原标题:AutoLayout自动布局,NSLayoutConstraint 视图约束使用
关键词: