Masonry 源码阅读

前言

Masonry 是 Objective-C 中用于 AutoLayout (see Understanding Auto Layout
) 的通用框架，一般用来代替原本 Apple AutoLayout 的繁琐的 AutoLayout 代码。

添加约束之前必须将view添加到superview里
对于要使用Auto Layout的控件需要关闭Autoresizing
创建并添加约束
更新约束

原生方式使用 Auto Layout

//viewTopLeft的leading与其superview的leading（左侧）对齐
[self.view addConstraint:[NSLayoutConstraint constraintWithItem:self.view attribute:NSLayoutAttributeLeading relatedBy:NSLayoutRelationEqual toItem:viewTopLeft attribute:NSLayoutAttributeLeading multiplier:1 constant:-10]];

//viewTopLeft的top与其superview的top对齐
[self.view addConstraint:[NSLayoutConstraint constraintWithItem:self.view attribute:NSLayoutAttributeTop relatedBy:NSLayoutRelationEqual toItem:viewTopLeft attribute:NSLayoutAttributeTop multiplier:1 constant:-10]];

//viewTopRight的top与viewTopLeft的top对齐
[self.view addConstraint:[NSLayoutConstraint constraintWithItem:viewTopRight attribute:NSLayoutAttributeTop relatedBy:NSLayoutRelationEqual toItem:viewTopLeft attribute:NSLayoutAttributeTop multiplier:1 constant:0]];

//viewTopRight的leading与viewTopLeft的trailing（右侧）对齐
[self.view addConstraint:[NSLayoutConstraint constraintWithItem:viewTopRight attribute:NSLayoutAttributeLeading relatedBy:NSLayoutRelationEqual toItem:viewTopLeft attribute:NSLayoutAttributeTrailing multiplier:1 constant:10]];

//viewTopRight的trailing与其superview的右侧对其
[self.view addConstraint:[NSLayoutConstraint constraintWithItem:viewTopRight attribute:NSLayoutAttributeTrailing relatedBy:NSLayoutRelationEqual toItem:self.view attribute:NSLayoutAttributeTrailing multiplier:1 constant:-10]];

//viewTopRight的宽与viewTopLeft宽相等
[self.view addConstraint:[NSLayoutConstraint constraintWithItem:viewTopRight attribute:NSLayoutAttributeWidth relatedBy:NSLayoutRelationEqual toItem:viewTopLeft attribute:NSLayoutAttributeWidth multiplier:1 constant:0]];

//viewTopRight的高与viewTopLeft高相等
[self.view addConstraint:[NSLayoutConstraint constraintWithItem:viewTopLeft attribute:NSLayoutAttributeHeight relatedBy:NSLayoutRelationEqual toItem:viewTopRight attribute:NSLayoutAttributeHeight multiplier:1 constant:0]];

Masonry 使用可以极大的简便这个过程

[button mas_makeConstraints:^(MASConstraintMaker *make) {
    make.centerX.equalTo(self.view);
    make.top.equalTo(self.view).with.offset(40);
    make.width.equalTo(@185);
    make.height.equalTo(@38);
}];

入口 (UIView+MASAdditions)

// 最常用的就是 make
- (NSArray *)mas_makeConstraints:(void(NS_NOESCAPE ^)(MASConstraintMaker *make))block;

// 当然还可以 update 和 remake
- (NSArray *)mas_updateConstraints:(void(NS_NOESCAPE ^)(MASConstraintMaker *make))block;

- (NSArray *)mas_remakeConstraints:(void(NS_NOESCAPE ^)(MASConstraintMaker *make))block;

make

- (NSArray *)mas_makeConstraints:(void(^)(MASConstraintMaker *))block {
    // 自动设置 self 使用 AutoLayout, 注意, secondView 并不会自动设置
    self.translatesAutoresizingMaskIntoConstraints = NO;

    // 创建 MASConstraintMaker，并让 maker 弱引用 self
    MASConstraintMaker *constraintMaker = [[MASConstraintMaker alloc] initWithView:self];

    // 执行 block, 给 maker 赋值, 不判空 ？？？
    block(constraintMaker);

    // 安装 maker 里面的约束
    return [constraintMaker install];
}

update

设置 update 标识值，其他与 make 一样

- (NSArray *)mas_updateConstraints:(void(^)(MASConstraintMaker *))block {
    self.translatesAutoresizingMaskIntoConstraints = NO;
    MASConstraintMaker *constraintMaker = [[MASConstraintMaker alloc] initWithView:self];
    constraintMaker.updateExisting = YES; // 设置 update 标识值
    block(constraintMaker);
    return [constraintMaker install];
}

remake

设置 remake 标识值，其他与 make 一样

- (NSArray *)mas_remakeConstraints:(void(^)(MASConstraintMaker *make))block {
    self.translatesAutoresizingMaskIntoConstraints = NO;
    MASConstraintMaker *constraintMaker = [[MASConstraintMaker alloc] initWithView:self];
    constraintMaker.removeExisting = YES; // 设置 remake 标识值
    block(constraintMaker);
    return [constraintMaker install];
}

总结

入口方法会自动设置了 firstView 使用 autolayout, 但是并不会设置 secondView。
入口方法内并没有见到明显的创建和安装约束(NSLayoutConstraint)相关的代码，推测应该在[constraintMaker install]实现了这个过程
所以 MASConstraintMaker 应该相当于一个Manager，可以储存所有firtView是self的 MASConstraint 容器

约束的创建与安装

@interface MASConstraintMaker () 

@property (nonatomic, weak) MAS_VIEW *view;
@property (nonatomic, strong) NSMutableArray *constraints;

@end

block内创建约束

链条的第一个 Attibute (MASConstraintMaker)

maker 会创建一个新的 MASConstraint 作为约束的容器，并将创建出的 constraint 的 delegate 指向 maker

@property (nonatomic, strong, readonly) MASConstraint *left;
@property (nonatomic, strong, readonly) MASConstraint *top;
@property (nonatomic, strong, readonly) MASConstraint *right;
@property (nonatomic, strong, readonly) MASConstraint *bottom;

....

left/centerX/width等

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

- (MASConstraint *)addConstraintWithLayoutAttribute:(NSLayoutAttribute)layoutAttribute {
    return [self constraint:nil addConstraintWithLayoutAttribute:layoutAttribute];
}

- (MASConstraint *)constraint:(MASConstraint *)constraint addConstraintWithLayoutAttribute:(NSLayoutAttribute)layoutAttribute {
    // 设置 firstViewAttribute 的 view 和 attr
    MASViewAttribute *viewAttribute = [[MASViewAttribute alloc] initWithView:self.view layoutAttribute:layoutAttribute];
    // MASViewConstraint 是 MASConstraint的子类
    MASViewConstraint *newConstraint = [[MASViewConstraint alloc] initWithFirstViewAttribute:viewAttribute];
    // 因为 参数传的都是 nil
    if ([constraint isKindOfClass:MASViewConstraint.class]) {...}
    if (!constraint) {
        newConstraint.delegate = self;
        // maker 上使用数组 存储了所有的数组
        [self.constraints addObject:newConstraint];
    }
    return newConstraint;
}

center/size/edges

- (MASConstraint *)edges {
    return [self addConstraintWithAttributes:MASAttributeTop | MASAttributeLeft | MASAttributeRight | MASAttributeBottom];
}

- (MASConstraint *)size {
    return [self addConstraintWithAttributes:MASAttributeWidth | MASAttributeHeight];
}

- (MASConstraint *)center {
    return [self addConstraintWithAttributes:MASAttributeCenterX | MASAttributeCenterY];
}

- (MASConstraint *)addConstraintWithAttributes:(MASAttribute)attrs {
    __unused MASAttribute anyAttribute = (MASAttributeLeft | MASAttributeRight | MASAttributeTop | MASAttributeBottom | MASAttributeLeading
                                          | MASAttributeTrailing | MASAttributeWidth | MASAttributeHeight | MASAttributeCenterX
                                          | MASAttributeCenterY | MASAttributeBaseline
#if (__IPHONE_OS_VERSION_MIN_REQUIRED >= 80000) || (__TV_OS_VERSION_MIN_REQUIRED >= 9000) || (__MAC_OS_X_VERSION_MIN_REQUIRED >= 101100)
                                          | MASAttributeFirstBaseline | MASAttributeLastBaseline
#endif
#if (__IPHONE_OS_VERSION_MIN_REQUIRED >= 80000) || (__TV_OS_VERSION_MIN_REQUIRED >= 9000)
                                          | MASAttributeLeftMargin | MASAttributeRightMargin | MASAttributeTopMargin | MASAttributeBottomMargin
                                          | MASAttributeLeadingMargin | MASAttributeTrailingMargin | MASAttributeCenterXWithinMargins
                                          | MASAttributeCenterYWithinMargins
#endif
                                          );

    NSAssert((attrs & anyAttribute) != 0, @"You didn't pass any attribute to make.attributes(...)");

    NSMutableArray *attributes = [NSMutableArray array];

    if (attrs & MASAttributeLeft) [attributes addObject:self.view.mas_left];
    if (attrs & MASAttributeRight) [attributes addObject:self.view.mas_right];
    if (attrs & MASAttributeTop) [attributes addObject:self.view.mas_top];
    if (attrs & MASAttributeBottom) [attributes addObject:self.view.mas_bottom];
    if (attrs & MASAttributeLeading) [attributes addObject:self.view.mas_leading];
    if (attrs & MASAttributeTrailing) [attributes addObject:self.view.mas_trailing];
    if (attrs & MASAttributeWidth) [attributes addObject:self.view.mas_width];
    if (attrs & MASAttributeHeight) [attributes addObject:self.view.mas_height];
    if (attrs & MASAttributeCenterX) [attributes addObject:self.view.mas_centerX];
    if (attrs & MASAttributeCenterY) [attributes addObject:self.view.mas_centerY];
    if (attrs & MASAttributeBaseline) [attributes addObject:self.view.mas_baseline];

#if (__IPHONE_OS_VERSION_MIN_REQUIRED >= 80000) || (__TV_OS_VERSION_MIN_REQUIRED >= 9000) || (__MAC_OS_X_VERSION_MIN_REQUIRED >= 101100)

    if (attrs & MASAttributeFirstBaseline) [attributes addObject:self.view.mas_firstBaseline];
    if (attrs & MASAttributeLastBaseline) [attributes addObject:self.view.mas_lastBaseline];

#endif

#if (__IPHONE_OS_VERSION_MIN_REQUIRED >= 80000) || (__TV_OS_VERSION_MIN_REQUIRED >= 9000)

    if (attrs & MASAttributeLeftMargin) [attributes addObject:self.view.mas_leftMargin];
    if (attrs & MASAttributeRightMargin) [attributes addObject:self.view.mas_rightMargin];
    if (attrs & MASAttributeTopMargin) [attributes addObject:self.view.mas_topMargin];
    if (attrs & MASAttributeBottomMargin) [attributes addObject:self.view.mas_bottomMargin];
    if (attrs & MASAttributeLeadingMargin) [attributes addObject:self.view.mas_leadingMargin];
    if (attrs & MASAttributeTrailingMargin) [attributes addObject:self.view.mas_trailingMargin];
    if (attrs & MASAttributeCenterXWithinMargins) [attributes addObject:self.view.mas_centerXWithinMargins];
    if (attrs & MASAttributeCenterYWithinMargins) [attributes addObject:self.view.mas_centerYWithinMargins];

#endif

    NSMutableArray *children = [NSMutableArray arrayWithCapacity:attributes.count];

    for (MASViewAttribute *a in attributes) {
        [children addObject:[[MASViewConstraint alloc] initWithFirstViewAttribute:a]];
    }

    MASCompositeConstraint *constraint = [[MASCompositeConstraint alloc] initWithChildren:children];
    constraint.delegate = self;
    [self.constraints addObject:constraint];
    return constraint;
}

链条上第二个 attribute

形如make.left.and.top.equalTo(@10);

会调用 MASConstraint 的 delegate 方法，也就是 maker 的constraint:addConstraintWithLayoutAttribute:的方法。

在该方法内，会将原约束容器替换成能够储存一组约束的容器(MASCompositeConstraint)

@interface MASConstraint : NSObject
- (MASConstraint *)left;
- (MASConstraint *)top;
- (MASConstraint *)right;
- (MASConstraint *)bottom;
...
@end

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

- (MASConstraint *)addConstraintWithLayoutAttribute:(NSLayoutAttribute)layoutAttribute {
    NSAssert(!self.hasLayoutRelation, @"Attributes should be chained before defining the constraint relation");

    return [self.delegate constraint:self addConstraintWithLayoutAttribute:layoutAttribute];
}

- (MASConstraint *)constraint:(MASConstraint *)constraint addConstraintWithLayoutAttribute:(NSLayoutAttribute)layoutAttribute {
    MASViewAttribute *viewAttribute = [[MASViewAttribute alloc] initWithView:self.view layoutAttribute:layoutAttribute];
    MASViewConstraint *newConstraint = [[MASViewConstraint alloc] initWithFirstViewAttribute:viewAttribute];
    if ([constraint isKindOfClass:MASViewConstraint.class]) {
        //replace with composite constraint
        NSArray *children = @[constraint, newConstraint];
        // MASCompositeConstraint 也是 MASConstraint 的子类，用来储存一组约束
        MASCompositeConstraint *compositeConstraint = [[MASCompositeConstraint alloc] initWithChildren:children];
        compositeConstraint.delegate = self;
        [self constraint:constraint shouldBeReplacedWithConstraint:compositeConstraint];
        return compositeConstraint;
    }
    if (!constraint) {...}
    return newConstraint;
}

- (void)constraint:(MASConstraint *)constraint shouldBeReplacedWithConstraint:(MASConstraint *)replacementConstraint {
    NSUInteger index = [self.constraints indexOfObject:constraint];
    NSAssert(index != NSNotFound, @"Could not find constraint %@", constraint);
    [self.constraints replaceObjectAtIndex:index withObject:replacementConstraint];
}

链条上 equalTo

@interface MASConstraint : NSObject

- (MASConstraint * (^)(id attr))equalTo;
- (MASConstraint * (^)(id attr))greaterThanOrEqualTo;
- (MASConstraint * (^)(id attr))lessThanOrEqualTo;

...
@end

- (MASConstraint * (^)(id))equalTo {
    return ^id(id attribute) {
        return self.equalToWithRelation(attribute, NSLayoutRelationEqual);
    };
}

- (MASConstraint * (^)(id, NSLayoutRelation))equalToWithRelation {
    return ^id(id attribute, NSLayoutRelation relation) {
        // 判断数组类型 ，主要用于处理此种情况 make.height.equalTo(@[view1.mas_height, view2.mas_height]);
        if ([attribute isKindOfClass:NSArray.class]) {
            NSAssert(!self.hasLayoutRelation, @"Redefinition of constraint relation");
            NSMutableArray *children = NSMutableArray.new;
            // 数组情况下，会遍历个数据创建约束数组
            for (id attr in attribute) {
                MASViewConstraint *viewConstraint = [self copy];
                // 依次设置 layoutRelation 和 secondViewAttribute
                viewConstraint.layoutRelation = relation;
                viewConstraint.secondViewAttribute = attr;
                [children addObject:viewConstraint];
            }
            // 根据约束数组，创建保存一组数据的约束
            MASCompositeConstraint *compositeConstraint = [[MASCompositeConstraint alloc] initWithChildren:children];
            compositeConstraint.delegate = self.delegate;
            [self.delegate constraint:self shouldBeReplacedWithConstraint:compositeConstraint];
            return compositeConstraint;
        } else {
            // 其余情况都直接存入secondViewAttribute
            NSAssert(!self.hasLayoutRelation || self.layoutRelation == relation && [attribute isKindOfClass:NSValue.class], @"Redefinition of constraint relation");
            // 主要是设置 layoutRelation 和 secondViewAttribute
            self.layoutRelation = relation;
            self.secondViewAttribute = attribute;
            return self;
        }
    };
}

// equalTo 接受三种基本参数 分别是 MAS_VIEW (iOS中就是 UIView) 、 NSValue 和 mas_left
- (void)setSecondViewAttribute:(id)secondViewAttribute {
    if ([secondViewAttribute isKindOfClass:NSValue.class]) {
        // 设置 width/center/size/edges, 注意 NSNumber 也是 NSValue 的子类
        [self setLayoutConstantWithValue:secondViewAttribute];
    } else if ([secondViewAttribute isKindOfClass:MAS_VIEW.class]) {
        // 如果是个 secondViewAttribute 是 view，那么 layoutAttribute 和 firstViewAttribute 相同
        _secondViewAttribute = [[MASViewAttribute alloc] initWithView:secondViewAttribute layoutAttribute:self.firstViewAttribute.layoutAttribute];
    } else if ([secondViewAttribute isKindOfClass:MASViewAttribute.class]) {
        // mas_left/mas_center 啥的
        _secondViewAttribute = secondViewAttribute;
    } else {
        NSAssert(NO, @"attempting to add unsupported attribute: %@", secondViewAttribute);
    }
}

// NSValue 的处理
- (void)setLayoutConstantWithValue:(NSValue *)value {
    if ([value isKindOfClass:NSNumber.class]) {
        self.offset = [(NSNumber *)value doubleValue];
    } else if (strcmp(value.objCType, @encode(CGPoint)) == 0) {
        CGPoint point;
        [value getValue:&point];
        self.centerOffset = point;
    } else if (strcmp(value.objCType, @encode(CGSize)) == 0) {
        CGSize size;
        [value getValue:&size];
        self.sizeOffset = size;
    } else if (strcmp(value.objCType, @encode(MASEdgeInsets)) == 0) {
        MASEdgeInsets insets;
        [value getValue:&insets];
        self.insets = insets;
    } else {
        NSAssert(NO, @"attempting to set layout constant with unsupported value: %@", value);
    }
}

mas_left

- (MASViewAttribute *)mas_left {
    // 储存 secondViewItem.view 和 secondViewItem.layoutAttribute
    return [[MASViewAttribute alloc] initWithView:self layoutAttribute:NSLayoutAttributeLeft];
}

链条上其他环节

with/and

用于语义的修饰，无实际作用

- (MASConstraint *)with {
    return self;
}

- (MASConstraint *)and {
    return self;
}

offset/priority/multipliedBy等

- (MASConstraint * (^)(CGFloat))offset {
    return ^id(CGFloat offset){
        self.offset = offset;
        return self;
    };
}
- (void)setOffset:(CGFloat)offset {
    self.layoutConstant = offset;
}

创建约束时可以使用

...

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;

...

mas_equalTo/mas_greaterThanOrEqualTo/mas_lessThanOrEqualTo

mas_equalTo 可以放入基本类型的参数比如：make.width.mas_equalTo(10);

#define mas_equalTo(...)                 equalTo(MASBoxValue((__VA_ARGS__)))
#define mas_greaterThanOrEqualTo(...)    greaterThanOrEqualTo(MASBoxValue((__VA_ARGS__)))
#define mas_lessThanOrEqualTo(...)       lessThanOrEqualTo(MASBoxValue((__VA_ARGS__)))

#define MASBoxValue(value) _MASBoxValue(@encode(__typeof__((value))), (value))

static inline id _MASBoxValue(const char *type, ...) {
    va_list v;
    va_start(v, type);
    id obj = nil;
    if (strcmp(type, @encode(id)) == 0) {
        id actual = va_arg(v, id);
        obj = actual;
    } else if (strcmp(type, @encode(CGPoint)) == 0) {
        CGPoint actual = (CGPoint)va_arg(v, CGPoint);
        obj = [NSValue value:&actual withObjCType:type];
    } else if (strcmp(type, @encode(double)) == 0) {
        double actual = (double)va_arg(v, double);
        obj = [NSNumber numberWithDouble:actual];
    } else {...}
    va_end(v);
    return obj;
}

约束的 install 过程

// MASConstraintMaker 的 install 方法
- (NSArray *)install {
    // remake 相关参数
    if (self.removeExisting) {
        // 移除当前 View 的所有约束
        NSArray *installedConstraints = [MASViewConstraint installedConstraintsForView:self.view];
        for (MASConstraint *constraint in installedConstraints) {
            // 调用约束的 uinstall 方法
            [constraint uninstall];
        }
    }
    NSArray *constraints = self.constraints.copy;
    for (MASConstraint *constraint in constraints) {
        constraint.updateExisting = self.updateExisting;
        // 调用约束的 install 方法
        [constraint install];
    }

    [self.constraints removeAllObjects];
    return constraints;
}

// MASCompositeConstraint 的 install 方法 ，递归地 把所有的 child 约束安装
- (void)install {
    for (MASConstraint *constraint in self.childConstraints) {
        constraint.updateExisting = self.updateExisting;
        [constraint install];
    }
}

// MASViewConstraint 的 install 方法
- (void)install {
    // 如果已经安装过， 不做操作
    if (self.hasBeenInstalled) {
        return;
    }

    //  iOS 8 新特性， active 参数
    if ([self supportsActiveProperty] && self.layoutConstraint) {
        self.layoutConstraint.active = YES;
        [self.firstViewAttribute.view.mas_installedConstraints addObject:self];
        return;
    }

    MAS_VIEW *firstLayoutItem = self.firstViewAttribute.item;
    NSLayoutAttribute firstLayoutAttribute = self.firstViewAttribute.layoutAttribute;
    MAS_VIEW *secondLayoutItem = self.secondViewAttribute.item;
    NSLayoutAttribute secondLayoutAttribute = self.secondViewAttribute.layoutAttribute;

    // alignment attributes must have a secondViewAttribute
    // therefore we assume that is refering to superview
    // eg make.left.equalTo(@10)
    if (!self.firstViewAttribute.isSizeAttribute && !self.secondViewAttribute) {
        secondLayoutItem = self.firstViewAttribute.view.superview;
        secondLayoutAttribute = firstLayoutAttribute;
    }

    // 注意！！！在这里创建约束LayoutConstraint (MASLayoutConstraint 是 NSLayoutConstraint 的子类)
    MASLayoutConstraint *layoutConstraint
        = [MASLayoutConstraint constraintWithItem:firstLayoutItem
                                        attribute:firstLayoutAttribute
                                        relatedBy:self.layoutRelation
                                           toItem:secondLayoutItem
                                        attribute:secondLayoutAttribute
                                       multiplier:self.layoutMultiplier
                                         constant:self.layoutConstant];

    // 设置 优先级
    layoutConstraint.priority = self.layoutPriority;
    layoutConstraint.mas_key = self.mas_key;

    if (self.secondViewAttribute.view) {
        // 如果secondViewAttribute 是 一个 view, 计算 公共的 super 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) {
        // 如果 firstViewAttribute 是 width height ， 约束安装到 firstViewAttribute.view
        self.installedView = self.firstViewAttribute.view;
    } else {
        // 其他情况安装到 firstViewAttribute.view.superview
        self.installedView = self.firstViewAttribute.view.superview;
    }

    MASLayoutConstraint *existingConstraint = nil;
    // update 标识符判定
    if (self.updateExisting) {
        existingConstraint = [self layoutConstraintSimilarTo:layoutConstraint];
    }
    // 如果是 update 入口来的， 并且查到约束并更新
    if (existingConstraint) {
        // just update the constant 注意 update 只能更新约束的 constant
        existingConstraint.constant = layoutConstraint.constant;
        self.layoutConstraint = existingConstraint;
    } else {
        // 其他情况 ， update 和 make 更新
        [self.installedView addConstraint:layoutConstraint];
        // 设置标志位
        self.layoutConstraint = layoutConstraint;
        // 设置 firstLayoutItem view.mas_installedConstraints,
        // 注意！这里只设置了 first view 的 install，remake 的时候也是移除了mas_installedConstraints 里的约束
        [firstLayoutItem.mas_installedConstraints addObject:self];
    }
}

其他

-[MASViewConstraint installedConstraintsForView]

+ (NSArray *)installedConstraintsForView:(MAS_VIEW *)view {
    return [view.mas_installedConstraints allObjects];
}

-[MASViewConstraint layoutConstraintSimilarTo:]

注意判断条件

只有 constant 不同,其他全部相同的约束才会判定为 similar

- (MASLayoutConstraint *)layoutConstraintSimilarTo:(MASLayoutConstraint *)layoutConstraint {
    // check if any constraints are the same apart from the only mutable property constant

    // go through constraints in reverse as we do not want to match auto-resizing or interface builder constraints
    // and they are likely to be added first.
    for (NSLayoutConstraint *existingConstraint in self.installedView.constraints.reverseObjectEnumerator) {
        if (![existingConstraint isKindOfClass:MASLayoutConstraint.class]) continue;
        if (existingConstraint.firstItem != layoutConstraint.firstItem) continue;
        if (existingConstraint.secondItem != layoutConstraint.secondItem) continue;
        if (existingConstraint.firstAttribute != layoutConstraint.firstAttribute) continue;
        if (existingConstraint.secondAttribute != layoutConstraint.secondAttribute) continue;
        if (existingConstraint.relation != layoutConstraint.relation) continue;
        if (existingConstraint.multiplier != layoutConstraint.multiplier) continue;
        if (existingConstraint.priority != layoutConstraint.priority) continue;

        return (id)existingConstraint;
    }
    return nil;
}

-[UIView mas_closestCommonSuperview]

计算公共的 superview 的算法

遍历两个 view 的 superview 链

- (instancetype)mas_closestCommonSuperview:(MAS_VIEW *)view {
    MAS_VIEW *closestCommonSuperview = nil;

    MAS_VIEW *secondViewSuperview = view;
    while (!closestCommonSuperview && secondViewSuperview) {
        MAS_VIEW *firstViewSuperview = self;
        while (!closestCommonSuperview && firstViewSuperview) {
            if (secondViewSuperview == firstViewSuperview) {
                closestCommonSuperview = secondViewSuperview;
            }
            firstViewSuperview = firstViewSuperview.superview;
        }
        secondViewSuperview = secondViewSuperview.superview;
    }
    return closestCommonSuperview;
}

-[MASConstraint uninstall]

// MASCompositeConstraint 容器递归 卸载 child 容器
- (void)uninstall {
    for (MASConstraint *constraint in self.childConstraints) {
        [constraint uninstall];
    }
}

// MASViewConstraint
- (void)uninstall {
    // 支持 active 方式话直接设置约束的active属性
    if ([self supportsActiveProperty]) {
        self.layoutConstraint.active = NO;
        [self.firstViewAttribute.view.mas_installedConstraints removeObject:self];
        return;
    }

    // 移除约束
    [self.installedView removeConstraint:self.layoutConstraint];
    self.layoutConstraint = nil;
    self.installedView = nil;

    // 从记录中删除
    [self.firstViewAttribute.view.mas_installedConstraints removeObject:self];
}

总结

make/update/remake 方法会自动设置 First View (self) 使用 AutoLayout，但是 secondView 并不会设置
remake 会移除 [self mas_make/update/remake:...] 方式添加的约束，不会移除作为 secondViewItem 的约束。
update 约束只会更新相似约束的 constant，不会能更新其他的参数
Masonry全量支持原生约束所有的设置参数，如multiplier、priority，但是代码看起来要整洁很多，这种思路很值得借鉴
Maker 管理 MASConstraint， MASConstraint 管理 layoutConstraint
MASConstraint的两个子类，一个是复合类型，一个是基础类型，这种多态的用法很常见
view.mas_installedConstraints 储存该 view 通过 mas_make/update/remake 方式安装的所有约束
mas_equalTo 的宏定义会使-[MASConstraint mas_equalTo:]永远不会触发，因为宏定义会在预处理阶段就替换成相关定义的代码