Masonry是一款轻量级的布局框架，采用方便的链式语法，可以更方便的帮助我们使用纯代码布局
下载地址：https://github.com/SnapKit/Masonry
导入方式：#import "Masonry.h"
约束的三种方法
//添加新约束
- (NSArray *)mas_makeConstraints:(void(NS_NOESCAPE ^)(MASConstraintMaker *make))block;
//更新约束，会覆盖之前的约束
- (NSArray *)mas_updateConstraints:(void(NS_NOESCAPE ^)(MASConstraintMaker *make))block;
//完全移除旧约束，添加新约束
- (NSArray *)mas_remakeConstraints:(void(NS_NOESCAPE ^)(MASConstraintMaker *make))block;
约束的基本属性
@property (nonatomic, strong, readonly) MASConstraint *left;
@property (nonatomic, strong, readonly) MASConstraint *top;
@property (nonatomic, strong, readonly) MASConstraint *right;
@property (nonatomic, strong, readonly) MASConstraint *bottom;
//首部
@property (nonatomic, strong, readonly) MASConstraint *leading;
//尾部
@property (nonatomic, strong, readonly) MASConstraint *trailing;
@property (nonatomic, strong, readonly) MASConstraint *width;
@property (nonatomic, strong, readonly) MASConstraint *height;
@property (nonatomic, strong, readonly) MASConstraint *centerX;
@property (nonatomic, strong, readonly) MASConstraint *centerY;
//文本基线
@property (nonatomic, strong, readonly) MASConstraint *baseline;
约束的特殊属性
//(top, left, bottom, right)
@property (nonatomic, strong, readonly) MASConstraint *edges;
//(width, height)
@property (nonatomic, strong, readonly) MASConstraint *size;
//(centerX, centerY)
@property (nonatomic, strong, readonly) MASConstraint *center;
注意点：
1.使用Masonry不需要设置控件的translatesAutoresizingMaskIntoConstraints属性为NO，mas_makeConstraints和mas_updateConstraints以及mas_remakeConstraints内部已经帮我们设置了;
- (NSArray *)mas_makeConstraints:(void(^)(MASConstraintMaker *))block {
self.translatesAutoresizingMaskIntoConstraints = NO;
MASConstraintMaker *constraintMaker = [[MASConstraintMaker alloc] initWithView:self];
block(constraintMaker);
return [constraintMaker install];
}
2.mas_makeConstraints和mas_updateConstraints以及mas_remakeConstraints的block是局部引用,block 里用到了 self，那 block 会保持一个 self 的引用，但是 self 并没有直接或者间接持有 block，所以不会造成循环引用。因此__weak typeof (self) weakSelf = self是没必要的
3.添加约束一定要放addSubview之后，否则程序会崩溃
基本使用
UIView *blueView = [[UIView alloc]init];
blueView.backgroundColor = [UIColor blueColor];
[self.view addSubview:blueView];
[blueView mas_makeConstraints:^(MASConstraintMaker *make) {
//设置blueView的中心点的x等于self.view的中心点的x
make.centerX.equalTo(self.view);
//设置blueView的顶部等于self.view的顶部，同时偏移30
make.top.equalTo(self.view).offset(30);
//设置宽高都为90
make.size.mas_equalTo(CGSizeMake(90, 90));
}];
UIView *blackView = [[UIView alloc]init];
blackView.backgroundColor = [UIColor blackColor];
[self.view addSubview:blackView];
[blackView mas_makeConstraints:^(MASConstraintMaker *make) {
make.top.equalTo(blueView.mas_bottom).offset(20);
make.right.equalTo(blueView.mas_left).offset(20);
make.size.mas_equalTo(CGSizeMake(100, 100));
}];
UIView *greenView = [[UIView alloc]init];
greenView.backgroundColor = [UIColor greenColor];
[self.view addSubview:greenView];
[greenView mas_makeConstraints:^(MASConstraintMaker *make) {
make.size.mas_equalTo(CGSizeMake(200, 50));
make.center.equalTo(self.view);
}];
equalTo和mas_equalTo的区别
先观察源码：
#define mas_equalTo(...) equalTo(MASBoxValue((__VA_ARGS__)))
mas_equalTo会对参数进行一个MASBoxValue（）操作，可以支持的类型是：NSNumber、 CGPoint、CGSize、UIEdgeInsets
/**
* Sets the constraint relation to NSLayoutRelationEqual
* returns a block which accepts one of the following:
* MASViewAttribute, UIView, NSValue, NSArray
* see readme for more details.
*/
- (MASConstraint * (^)(id attr))equalTo;
equalTo并没有MASBoxValue（）操作，源码的注释上说了equalTo支持的类型是：MASViewAttribute, UIView, NSValue, NSArray
为了方便编码的2个宏
1.#define MAS_SHORTHAND：可以省略'mas_'前缀
2.#define MAS_SHORTHAND_GLOBALS：自动将结构体包装成 NSValue，而无需再使用 mas_equalTo，其源码如下：
#ifdef MAS_SHORTHAND_GLOBALS
#define equalTo(...) mas_equalTo(__VA_ARGS__)
