开源项目Masonry旨在让自动布局（Auto Layout）的代码更简洁，可读性更强。

Masonry is a light-weight layout framework which wraps AutoLayout with a nicer syntax. Masonry has its own layout DSL which provides a chainable way of describing your NSLayoutConstraints which results in layout code that is more concise and readable. Masonry supports iOS and Mac OS X.

Masonry 是一种领域特定语言（DSL），为自动布局的所有功能提供便捷的方法，包括建立和修改约束、存取属性、设置优先级以及调试支持。

GitHub上的示例代码

我们通过作者给出的代码来详细体会Masonry的典型用法及其简洁的语法。首先你得在需要的类中引入Masonry.h

//define this constant if you want to use Masonry without the 'mas_' prefix
#define MAS_SHORTHAND  //方法名和属性名简略写法

//define this constant if you want to enable auto-boxing for default syntax
#define MAS_SHORTHAND_GLOBALS  //设置约束的block属性简略写法(自动转换数值类型)

UIView *view1 = [[UIView alloc]init];
view1.backgroundColor = UIColor.greenColor;
view1.layer.borderColor = UIColor.blackColor.CGColor;
view1.layer.borderWidth = 2;
[self addSubview:view1];

UIView *view2 = [[UIView alloc]init];
view2.backgroundColor = UIColor.redColor;
view2.layer.borderColor = UIColor.blackColor.CGColor;
view2.layer.borderWidth = 2;
[self addSubview:view2];

UIView *view3 = [[UIView alloc]init];
view3.backgroundColor = UIColor.blueColor;
view3.layer.borderColor = UIColor.blackColor.CGColor;
view3.layer.borderWidth = 2;
[self addSubview:view3];

UIView *superview = self;
int padding = 10;

[view1 makeConstraints:^(MASConstraintMaker *make) {
    make.top.greaterThanOrEqualTo(superview.top).offset(padding);
    make.left.equalTo(superview.left).offset(padding);
    make.bottom.equalTo(view3.top).offset(-padding);
    make.right.equalTo(view2.left).offset(-padding);
    make.width.equalTo(view2.width);
    
    make.height.equalTo(@[view2.height,view3.height]);
}];

[view2 mas_makeConstraints:^(MASConstrainMaker *make) {
    make.top.equalTo(superview.mas_top).with.offset(padding);
    make.left.equalTo(view1.mas_right).offset(padding);
    make.bottom.equalTo(view3.mas_top).offset(-padding);
    make.right.equalTo(superview.mas_right).offset(-padding);
    make.width.equalTo(view1.mas_width);
    
    make.height.equalTo(@[view1,view3]);
}];

[view3 mas_makeConstraints:^(MASConstraintMaker *make) {
    make.top.equalTo(view1.mas_bottom).offset(padding);
    make.left.equalTo(superview.mas_left).offset(padding);
    make.bottom.equalTo(superview.mas_bottom).offset(-padding);
    make.right.equalTo(superview.mas_right).offset(-padding);
    
    make.height.equalTo(@[view1.mas_height,view2.mas_height]);
}];

代码中使用了makeConstraints和mas_makeConstraints方法，其实是一种方法，前者是后者的简略写法，如果想使用前者，就必须在引入Masonry.h前define MAS_SHORTHAND，不然不起效果。同样top和mas_top也是如此。下面我们分析makeConstraints方法。

相似的方法还有updateConstraints，remakeConstraints

-(NSArray *)mas_makeConstraints:(void(^)(MASContraintMaker *))block {
    //使用Auto Layout前必须关闭AutoresizingMask
    self.translatesAutoresizingMaskIntoConstraints = NO;
    MASConstraintMaker *constraintMaker = [[MASConstraintMaker alloc]initWithView:self];
    //添加约束
    block(constraintMaker);
    //开始布局
    return [constraintMaker install];
}

这段代码的用处就是将block中设置的约束进行初始化，install中的方法即是调用系统Auto Layout方法，因此我们只要关心block块中方法即可。

让我们回顾下经典设置frame方法

self.view.frame = CGRectMake(<#CGFloat x#>, <#CGFloat y#>, <#CGFloat width#>, <#CGFloat height#>);

frame中使用了四个属性控制view的形状和位置，这在iPhone4s的时代还没有多大的问题。随着iPhone屏幕的增大，特别是iPhone6屏幕宽度的增加，你会发现在iPhone5上运行好好的项目在iPhone6上右边就会空出一小块。那么就必须再加两个属性一起来控制

我们先来看看Masonry给我们带来了哪些属性和方法

1.属性

left, top, right, bottom, leading, trailing, width, height, centerX, centerY, baseline

2.基础

equalTo, greaterThanOrEqualTo, lessThanOrEqualTo

这里很有意思，作者重写block的get方法将具体set方法放进最里层，和我们一般使用block有些不一样（其实还是先set后get，本质无区别）

3.进阶

insets, sizeOffset, centerOffset, offset

4.优先级

priorityLow, priorityMedium, priorityHigh

5.链式语言

with, and

起连接作用，并无实际意义