本章大致描述一下Masonry是如何支持链式语法的，并且对框架的其他一些文件做一些描述
第一部分 了解一下链式语法是如何实现的###
实际上前面两篇文章已经讲述的差不多了，如果看过源码，应该就会很轻松的知道，Masonry是如何支持链式语法的结构。
还是拿一个例子的讲解一下吧,（下方代码已删除不甚相关的代码）
make.top.left究竟发生了什么？
我们知道make.top返回的是MASConstraint对象，更确切的说是MASViewConstraint对象，
上篇文章中我们知道，对MASConstraint调用top、left等，会返回一个MASCompositeConstraint对象；
这个对象，会包含一个数组，在这个例子中存放的就是layoutAttribute分别为top和left的
两个MASViewConstraint对象。
1、MASConstraint的left方法：
- (MASConstraint *)left {
return [self addConstraintWithLayoutAttribute:NSLayoutAttributeLeft];
}
它会跳转到MASViewConstraint的addConstraintWithLayout...方法
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2、MASViewConstraint的addConstraintWithLayout...方法
- (MASConstraint *)addConstraintWithLayoutAttribute:(NSLayoutAttribute)layoutAttribute {
return [self.delegate constraint:self addConstraintWithLayoutAttribute:layoutAttribute];
}
它会调用delegate的constraint...delegate就是MASConstraintMaker，来看看吧
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3、MASConstraintMaker的代理方法
- (MASConstraint *)constraint:(MASConstraint *)constraint addConstraintWithLayoutAttribute:(NSLayoutAttribute)layoutAttribute {
MASCompositeConstraint *compositeConstraint = [[MASCompositeConstraint alloc] initWithChildren:children];
[self constraint:constraint shouldBeReplacedWithConstraint:compositeConstraint];
return compositeConstraint;
}
第二部分 一些Category###
1、NSArray (MASAdditions)
array内部是view，遍历array，逐一对view调用这些方法
- (NSArray *)mas_makeConstraints:(void (^)(MASConstraintMaker *make))block;
- (NSArray *)mas_updateConstraints:(void (^)(MASConstraintMaker *make))block;
- (NSArray *)mas_remakeConstraints:(void (^)(MASConstraintMaker *make))block;
2、View+MASAdditions
我们平时，也可以对view调用一些方法例如：
@property (nonatomic, strong, readonly) MASViewAttribute *mas_left;
@property (nonatomic, strong, readonly) MASViewAttribute *mas_top;
@property (nonatomic, strong, readonly) MASViewAttribute *mas_right;
@property (nonatomic, strong, readonly) MASViewAttribute *mas_bottom;
@property (nonatomic, strong, readonly) MASViewAttribute *mas_leading;
@property (nonatomic, strong, readonly) MASViewAttribute *mas_trailing;
@property (nonatomic, strong, readonly) MASViewAttribute *mas_width;
@property (nonatomic, strong, readonly) MASViewAttribute *mas_height;
@property (nonatomic, strong, readonly) MASViewAttribute *mas_centerX;
@property (nonatomic, strong, readonly) MASViewAttribute *mas_centerY;
@property (nonatomic, strong, readonly) MASViewAttribute *mas_baseline;
可以看到，返回的是MASViewAttribute对象
剩下的就是比较简单的mas_makeConstraint...
3、ViewController+MASAdditions
@property (nonatomic, strong, readonly) MASViewAttribute *mas_topLayoutGuide;
@property (nonatomic, strong, readonly) MASViewAttribute *mas_bottomLayoutGuide;
@property (nonatomic, strong, readonly) MASViewAttribute *mas_topLayoutGuideTop;
@property (nonatomic, strong, readonly) MASViewAttribute *mas_topLayoutGuideBottom;
@property (nonatomic, strong, readonly) MASViewAttribute *mas_bottomLayoutGuideTop;
@property (nonatomic, strong, readonly) MASViewAttribute *mas_bottomLayoutGuideBottom;
这些就是对齐self.view的顶部导航栏和底步tabbar的顶部了，底部之类的
