Objective-C语言——AutoLayout自动布局

#import "ViewController.h"

@interface ViewController ()

@end

@implementation ViewController

- (void)viewDidLoad {
[super
viewDidLoad];

/*
AutoLayout 由来
iOS6之后出现的一种新的布局方式，用于取代原先的 Autoresizing
系统的布局方式

AutoLayer 是指定视图和父视图
或 视图和兄弟视图的关系来布局

在 AutoLayer
当中，我们使用约束来描述视图与视图之间的关系

OC 专门为开发者封装了一个类 NSLayoutConstraint
来帮助开发者描述布局
*/

// [NSLayoutConstraint constraintWithItem:<#(nonnull id)#> attribute:<#(NSLayoutAttribute)#> relatedBy:<#(NSLayoutRelation)#> toItem:<#(nullable id)#> attribute:<#(NSLayoutAttribute)#> multiplier:<#(CGFloat)#> constant:<#(CGFloat)#>];
/*
参数的意义:
Item:约束中两个视图对象
attribute:描述视图的对齐特征
relatedBy：描述两个视图 attribute
关系
multiplier：缩放比例
constant：偏移量

视图1（Item）.属性（attribute）
关系（relatedBy）
视图2（Item）.属性（attribute）*缩放比例（multiplier）
+ 偏移量（constant）

视图1.左边 ==
视图2.左边 * 1 + 0
[NSLayoutConstraint constraintWithItem:视图1 attribute:左边 relatedBy:等于 toItem:视图2
[attribute:左边 multiplier:1 constant:0];

视图1.宽度 == 100
[NSLayoutConstraint constraintWithItem:视图1 attribute:宽度 relatedBy:等于 toItem:
nil attribute:宽度 multiplier:1 constant:100];

*/
UIView *view1 = [UIView
new];
view1.backgroundColor = [UIColor
purpleColor];
//启动 autoLayer
布局
view1.translatesAutoresizingMaskIntoConstraints =
NO;
[self.view
addSubview:view1];
// X轴
NSLayoutConstraint *constraintX = [NSLayoutConstraint
constraintWithItem:view1 attribute:NSLayoutAttributeCenterX
relatedBy:NSLayoutRelationEqual
toItem:self.view
attribute:NSLayoutAttributeCenterX
multiplier:1
constant:0];
[self.view
addConstraint:constraintX];

// Y轴
NSLayoutConstraint *constraintY = [NSLayoutConstraint
constraintWithItem:view1 attribute:NSLayoutAttributeCenterY
relatedBy:NSLayoutRelationEqual
toItem:self.view
attribute:NSLayoutAttributeCenterY
multiplier:1
constant:0];
[self.view
addConstraint:constraintY];

// 宽度
NSLayoutConstraint *constraintWidth = [NSLayoutConstraint
constraintWithItem:view1 attribute:NSLayoutAttributeWidth
relatedBy:NSLayoutRelationEqual
toItem:nil
attribute:NSLayoutAttributeWidth
multiplier:1
constant:100];
[self.view
addConstraint:constraintWidth];
//高度
NSLayoutConstraint *constraintHeight = [NSLayoutConstraint
constraintWithItem:view1 attribute:NSLayoutAttributeHeight
relatedBy:NSLayoutRelationEqual
toItem:nil
attribute:NSLayoutAttributeHeight
multiplier:1
constant:100];

[self.view
addConstraint:constraintHeight];

UIView *view2 = [[UIView
alloc] init];
view2.backgroundColor = [UIColor
yellowColor];

//布局启动
view2.translatesAutoresizingMaskIntoConstraints =
NO;
[self.view
addSubview:view2];

NSLayoutConstraint *constraintX2 = [NSLayoutConstraint
constraintWithItem:view2 attribute:NSLayoutAttributeLeading
relatedBy:NSLayoutRelationEqual
toItem:view1 attribute:NSLayoutAttributeTrailing
multiplier:1
constant:0];
[self.view
addConstraint:constraintX2];

NSLayoutConstraint *constraintY2 = [NSLayoutConstraint
constraintWithItem:view2 attribute:NSLayoutAttributeTop
relatedBy:NSLayoutRelationEqual
toItem:view1 attribute:NSLayoutAttributeBottom
multiplier:1
constant:0];
[self.view
addConstraint:constraintY2];

NSLayoutConstraint *constraintWidth2 = [NSLayoutConstraint
constraintWithItem:view2 attribute:NSLayoutAttributeWidth
relatedBy:NSLayoutRelationEqual
toItem:view1 attribute:NSLayoutAttributeWidth
multiplier:0.5
constant:0];
[self.view
addConstraint:constraintWidth2];

NSLayoutConstraint *constraintHeight2 = [NSLayoutConstraint
constraintWithItem:view2 attribute:NSLayoutAttributeHeight
relatedBy:NSLayoutRelationEqual
toItem:view1 attribute:NSLayoutAttributeHeight
multiplier:1
constant:0];
[self.view
addConstraint:constraintHeight2];

}

- (void)didReceiveMemoryWarning {
[super
didReceiveMemoryWarning];
// Dispose of any resources that can be recreated.
}

@end