Masonry浅析

首先我们可以先写下最常用的代码

 [btn mas_makeConstraints:^(MASConstraintMaker *make) {        make.left.top.equalTo(@10);        make.right.bottom.equalTo(@10);}

点进这个方法mas_makeConstraints，我们会看到下面的这样的代码，先把autoresizing先关闭，autoresizing其实就是根据父控件的大小去拉伸的，然后去创建了这个MASConstraintMaker类的对象，其实这个类的对象也就是make就是约束制造者。

- (NSArray *)mas_makeConstraints:(void(^)(MASConstraintMaker *))block {    self.translatesAutoresizingMaskIntoConstraints = NO;    MASConstraintMaker *constraintMaker = [[MASConstraintMaker alloc] initWithView:self];    block(constraintMaker);    return [constraintMaker install];}

我们再去看上面的initWithView的代码，其实就是去绑定了一个view，然后去创建了一个约束数组。

- (id)initWithView:(MAS_VIEW *)view {    self = [super init];    if (!self) return nil;        self.view = view;    self.constraints = NSMutableArray.new;        return self;}

然后那个其实就是把constraintMaker传递给外面，然后调用外面写好的block。

block(constraintMaker)

再就是去安装约束点击进入install的方法，其实就是先把view之前的约束先清空了，然后再把约束数组中有的约束给安装上去

[constraintMaker install]

也就是下面的代码

- (NSArray *)install {    if (self.removeExisting) {        NSArray *installedConstraints = [MASViewConstraint installedConstraintsForView:self.view];        for (MASConstraint *constraint in installedConstraints) {            [constraint uninstall];        }    }    NSArray *constraints = self.constraints.copy;    for (MASConstraint *constraint in constraints) {        constraint.updateExisting = self.updateExisting;        [constraint install];    }    [self.constraints removeAllObjects];    return constraints;}

之前我们再去看看单个约束安装的代码也就是下面这个install的方法

[constraint install];

我们点进去看看，注意的是我们这里点击的是MASViewConstraint，因为我们添加的是left，top等约束，就不复制所有的代码了，复制一部分，其实就是在做创建约束和一些其他事情的处理。

MASLayoutConstraint *layoutConstraint        = [MASLayoutConstraint constraintWithItem:firstLayoutItem                                        attribute:firstLayoutAttribute                                        relatedBy:self.layoutRelation                                           toItem:secondLayoutItem                                        attribute:secondLayoutAttribute                                       multiplier:self.layoutMultiplier                                         constant:self.layoutConstant];        layoutConstraint.priority = self.layoutPriority;    layoutConstraint.mas_key = self.mas_key;        if (self.secondViewAttribute.view) {        MAS_VIEW *closestCommonSuperview = [self.firstViewAttribute.view mas_closestCommonSuperview:self.secondViewAttribute.view];        NSAssert(closestCommonSuperview,                 @"couldn't find a common superview for %@ and %@",                 self.firstViewAttribute.view, self.secondViewAttribute.view);        self.installedView = closestCommonSuperview;    } else if (self.firstViewAttribute.isSizeAttribute) {        self.installedView = self.firstViewAttribute.view;    } else {        self.installedView = self.firstViewAttribute.view.superview;    }

然后我们再去点击我们设置的left，top等代码进去看其实就是去添加个约束属性

- (MASConstraint *)left {    return [self addConstraintWithLayoutAttribute:NSLayoutAttributeLeft];}

然后再这样一层一层的点击进去，会发现其实就是去给self.view去绑定属性，之后去创建MASViewConstraint这个类的对象，然后设置代理之后添加进约束数组中，截取一部分代码

    MASViewAttribute *viewAttribute = [[MASViewAttribute alloc] initWithView:self.view layoutAttribute:layoutAttribute];    MASViewConstraint *newConstraint = [[MASViewConstraint alloc] initWithFirstViewAttribute:viewAttribute];   if (!constraint) {        newConstraint.delegate = self;        [self.constraints addObject:newConstraint];    }