Masonry中的mas_makeConstraints方法
一、简单介绍
我们一般来说会这样进行使用
[view mas_makeConstraints:^(MASConstraintMaker *make) {
//这个使用的就是MASCompositeConstraint类型的
make.left.top.width.height.mas_equalTo(100).multipliedBy(1);
//这个使用的就是单个单个的MASViewConstraint
// make.left.mas_equalTo(100);
// make.top.mas_equalTo(100);
// make.width.mas_equalTo(100);
// make.height.mas_equalTo(100);
}];- (NSArray *)mas_makeConstraints:(void(^)(MASConstraintMaker *))block {
self.translatesAutoresizingMaskIntoConstraints = NO;
//创建MASConstraintMaker对象，就是我们block中的make，
MASConstraintMaker *constraintMaker = [[MASConstraintMaker alloc] initWithView:self];
//执行block
block(constraintMaker);
//安装install 约束
return [constraintMaker install];
}我们再去看看install的方法，其内部就是去先去获取view的所有的约束，然后进行移除，之后再去安装新的约束
- (NSArray *)install {
//判断是否要移除已经存在的约束，这里其实就是在使用re_make的时候这个会为YES
if (self.removeExisting) {
//获取view的所有的约束
NSArray *installedConstraints = [MASViewConstraint installedConstraintsForView:self.view];
for (MASConstraint *constraint in installedConstraints) {
[constraint uninstall];
}
}
//安装新约束
NSArray *constraints = self.constraints.copy;
for (MASConstraint *constraint in constraints) {
constraint.updateExisting = self.updateExisting;
[constraint install];
}
[self.constraints removeAllObjects];
return constraints;
}这个时候大家肯定很疑惑，What? 我约束都还没有添加，怎么直接开始遍历了？ 其实我们在block中执行make.left.width这个时候其实就已经在添加约束了，先来看下在调用.left的时候调用的MASConstraintMaker的方法
返回值是MASConstriant，所以我们在make.left之后再.width其实是调用的是MASConstraint的width方法了其中这个方法是个抽象方法定义在MASConstraint类中。
然后之后调用的就是MASViewConstraint中的addConstraintWithLayoutAttribute方法
然后我们点进上面的self.delegate 调用的方法进去看看，调用的是下面的方法，这里其实就可以理解为把left和Width的约束进行合并成为一个约束集合类
- (MASConstraint *)constraint:(MASConstraint *)constraint addConstraintWithLayoutAttribute:(NSLayoutAttribute)layoutAttribute {
//根据layoutAttribute属性也就是NSLayoutAttributeTop这些初始化MASViewAttribute类
MASViewAttribute *viewAttribute = [[MASViewAttribute alloc] initWithView:self.view layoutAttribute:layoutAttribute];
//根据viewAttribute创建MASViewConstraint对象
MASViewConstraint *newConstraint = [[MASViewConstraint alloc] initWithFirstViewAttribute:viewAttribute];
//如果有constraint的话，就进行合并成一个composite Constraint，这个是一个集合类
if ([constraint isKindOfClass:MASViewConstraint.class]) {
//replace with composite constraint
NSArray *children = @[constraint, newConstraint];
/*
MASCompositeConstraint：约束的集合类。内部有一个数组，可以保存多个MASViewConstraint。对MASCompositeConstraint调用方法实际等于
对其内部的所有MASViewConstraint调用方法
*/
MASCompositeConstraint *compositeConstraint = [[MASCompositeConstraint alloc] initWithChildren:children];
compositeConstraint.delegate = self;
//在self.constraint进行替换
[self constraint:constraint shouldBeReplacedWithConstraint:compositeConstraint];
return compositeConstraint;
}
//如果不存在constraint那就去设置newConstraint，然后添加进入约束数组
if (!constraint) {
newConstraint.delegate = self;
//add
[self.constraints addObject:newConstraint];
}
return newConstraint;
}再去看看constraintMaker中的install方法中的NSArray *installedConstraints = [MASViewConstraint installedConstraintsForView:self.view];里面的installedConstraintsForView方法内部调用了mas_installedConstraints的get方法，然后去获取所有的对象，也就是这里面的方法
+ (NSArray *)installedConstraintsForView:(MAS_VIEW *)view {
return [view.mas_installedConstraints allObjects];
}再去看看这个get方法其实就是运用了运行时的知识
- (NSMutableSet *)mas_installedConstraints {
NSMutableSet *constraints = objc_getAssociatedObject(self, &kInstalledConstraintsKey);
if (!constraints) {
constraints = [NSMutableSet set];
//相当于 setValue:forKey 进行关联value对象
objc_setAssociatedObject(self, &kInstalledConstraintsKey, constraints, OBJC_ASSOCIATION_RETAIN_NONATOMIC);
}
return constraints;
}然后再去看看关于uninstall方法的实现，这个方法的实现就是先判断能不能相应active方法，因为这个属性是ios8才出现的
- (void)uninstall {
if ([self supportsActiveProperty]) {
//设置约束不可用
self.layoutConstraint.active = NO;
//移除约束
[self.firstViewAttribute.view.mas_installedConstraints removeObject:self];
return;
}
//来到下面表示不能响应active方法，做了适配
[self.installedView removeConstraint:self.layoutConstraint];
self.layoutConstraint = nil;
self.installedView = nil;
[self.firstViewAttribute.view.mas_installedConstraints removeObject:self];
}我们再去看看安装新约束当中的install方法
- (void)install {
//判断约束是否已经存在，以及是否已经处理激活状态其实就是使用状态
if (self.hasBeenInstalled) {
return;
}
//判断布局是否可以响应active这个方法的设置，判断layoutConstriant存不存在
if ([self supportsActiveProperty] && self.layoutConstraint) {
//iOS 6.0或者7.0调用addConstraints
//[self.view addConstraints:@[leftConstraint, rightConstraint, topConstraint, heightConstraint]];
//iOS 8.0以后设置active属性值 就可以去使用约束了
self.layoutConstraint.active = YES;
//这里会进行添加约束
[self.firstViewAttribute.view.mas_installedConstraints addObject:self];
return;
}
//获取item，获取第一个viewattribute的item也就是constraintWithItem中的item
MAS_VIEW *firstLayoutItem = self.firstViewAttribute.item;
//获取属性比如说NSLayoutAttributeTop
NSLayoutAttribute firstLayoutAttribute = self.firstViewAttribute.layoutAttribute;
//获取约束的第二个view
MAS_VIEW *secondLayoutItem = self.secondViewAttribute.item;
//获取layout的属性
NSLayoutAttribute secondLayoutAttribute = self.secondViewAttribute.layoutAttribute;
// alignment attributes must have a secondViewAttribute
// therefore we assume that is refering to superview
// eg make.left.equalTo(@10)
//判断是不是要设置的是size的约束，以及判断第二个约束的属性是不是为空如果为空，就去设置下面的属性
if (!self.firstViewAttribute.isSizeAttribute && !self.secondViewAttribute) {
secondLayoutItem = self.firstViewAttribute.view.superview;
secondLayoutAttribute = firstLayoutAttribute;
}
//创建约束布局 self.layoutRelation就是约束关系
MASLayoutConstraint *layoutConstraint
= [MASLayoutConstraint constraintWithItem:firstLayoutItem
attribute:firstLayoutAttribute
relatedBy:self.layoutRelation
toItem:secondLayoutItem
attribute:secondLayoutAttribute
multiplier:self.layoutMultiplier
constant:self.layoutConstant];
//设置约束的优先级
layoutConstraint.priority = self.layoutPriority;
/*
当约束冲突发生的时候，我们可以设置view的key来定位是哪个view
redView.mas_key = @"redView";
greenView.mas_key = @"greenView";
blueView.mas_key = @"blueView";
若是觉得这样一个个设置比较繁琐，怎么办呢，Masonry则提供了批量设置的宏MASAttachKeys
MASAttachKeys(redView,greenView,blueView); //一句代码即可全部设置
*/
layoutConstraint.mas_key = self.mas_key;
//判断第二个view是否存在
if (self.secondViewAttribute.view) {
//寻找两个视图的公共父视图，这个方法其实就是循环遍历寻找
MAS_VIEW *closestCommonSuperview = [self.firstViewAttribute.view mas_closestCommonSuperview:self.secondViewAttribute.view];
//断言判断公共父视图存不存在
NSAssert(closestCommonSuperview,
@"couldn't find a common superview for %@ and %@",
self.firstViewAttribute.view, self.secondViewAttribute.view);
//设置安装约束的视图
self.installedView = closestCommonSuperview;
}
//如果是设置view的宽度和高度的，设置安装越苏的视图为第一个view
else if (self.firstViewAttribute.isSizeAttribute) {
self.installedView = self.firstViewAttribute.view;
}
//否则就给superview进行设置
else {
self.installedView = self.firstViewAttribute.view.superview;
}
MASLayoutConstraint *existingConstraint = nil;
//判断是否是更新约束，这里判断的条件就是是否只存在constant不一样的视图
if (self.updateExisting) {
existingConstraint = [self layoutConstraintSimilarTo:layoutConstraint];
}
//如果已经存在只有constant不一样的约束，就去更新constant
if (existingConstraint) {
// just update the constant
existingConstraint.constant = layoutConstraint.constant;
self.layoutConstraint = existingConstraint;
}
//如果没有存在的只有constant不一样的约束，就去添加约束
else {
[self.installedView addConstraint:layoutConstraint];
self.layoutConstraint = layoutConstraint;
[firstLayoutItem.mas_installedConstraints addObject:self];
}
}关于上面判断是否只存在constant不一样的视图的方法
- (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.
//从后面往前面遍历这个数组
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;
}
关于self.hasBeenInstalled其实就是调用了下面的方法
- (BOOL)hasBeenInstalled {
return (self.layoutConstraint != nil) && [self isActive];
}其实Masonry就是对系统本身的自动布局的layout进行了封装
