一、封装结构
MASConstraint 约束
MASCompositeConstraint 一组约束//
MASViewConstraint 一个约束//囊括整个约束计算公式的所有数据（firstViewAttribute、secondViewAttribute、常量值、关系、优先级、比例值。用于链式操作的“delegate”）。
MASConstraintMaker 创建约束的工厂
MASViewAttribute 封装 View+约束， 等式两边的计算因子（结构相当于元组类型）
View+MASAdditions 入口（ 创建计算MASViewAttribute的工厂 ）
ViewController+MASAdditions 入口（ 创建MASViewAttribute的工厂 ）
NSArray+MASAdditions 对数组中的每一个view做相同的约束操作。 批量操作。还提供了一套统一布局的方法。（固定大小，固定间距）
MASUtilities 用来将任何类型（数值类型，对象类型）， 转化为对象类型
二、链式
1、
make.height.inset(10);//无效。因为layoutAttribute是NSLayoutAttributeHeight
make.height.mas_equalTo(10);
2、
make.height.mas_equalTo(10); // 如果是NSValue类型。给firstView设置
make.height.mas_equalTo(self.view);// 如果是View类型， 创建secondViewAttribute。并且属性NSLayoutAttribute与firstViewAttribute相同
make.height.mas_equalTo(self.view.mas_height); //如果是计算因子类型。则直接赋值。
3，
链式如何实现的？
MASCompositeConstraint（一组约束） 代理。
MASConstraintMaker （创建约束的工厂） 代理。
//操作1
make.top.offset(0);
make.bottom.offset(0);
make.size.sizeOffset(CGSizeZero);
//链式1
make.top.left.right.offset(0);
//链式2
make.edges.top.left.offset(0);
//链式3
make.top.equalTo(@20).equalTo(@30);
// 不支持这种链式： 后面的-10会覆盖前面的10
make.top.left.equalTo(@10).bottom.right.equalTo(@(-10));
MASLayoutConstraint *existingConstraint = nil;
if (self.updateExisting) {
existingConstraint = [self layoutConstraintSimilarTo:layoutConstraint];
}
if (existingConstraint) {
// just update the constant
existingConstraint.constant = layoutConstraint.constant;
self.layoutConstraint = existingConstraint;
}////////
//不支持重复添加约束
//equalTo(v2.mas_left)第二个约束，重复添加。
//NSAssert(!self.hasLayoutRelation || self.layoutRelation == relation && [attribute isKindOfClass:NSValue.class], @"Redefinition of constraint relation");
make.top.left.equalTo(v2.mas_top).equalTo(v2.mas_left).equalTo(@0);
// 不支持这种链式
make.center.size.edges
masConstraint
#pragma mark - attribute chaining
- (MASConstraint *)addConstraintWithLayoutAttribute:(NSLayoutAttribute)layoutAttribute {
NSAssert(!self.hasLayoutRelation, @"Attributes should be chained before defining the constraint relation");
return [self.delegate constraint:self addConstraintWithLayoutAttribute:layoutAttribute];
}
masCompositeConstraint
#pragma mark - attribute chaining
- (MASConstraint *)addConstraintWithLayoutAttribute:(NSLayoutAttribute)layoutAttribute {
[self constraint:self addConstraintWithLayoutAttribute:layoutAttribute];
return self;
}
- (MASConstraint *)constraint:(MASConstraint __unused *)constraint addConstraintWithLayoutAttribute:(NSLayoutAttribute)layoutAttribute {
id<MASConstraintDelegate> strongDelegate = self.delegate;
MASConstraint *newConstraint = [strongDelegate constraint:self addConstraintWithLayoutAttribute:layoutAttribute];
newConstraint.delegate = self;
[self.childConstraints addObject:newConstraint];
return newConstraint;
}
- (void)constraint:(MASConstraint *)constraint shouldBeReplacedWithConstraint:(MASConstraint *)replacementConstraint {
NSUInteger index = [self.childConstraints indexOfObject:constraint];
NSAssert(index != NSNotFound, @"Could not find constraint %@", constraint);
[self.childConstraints replaceObjectAtIndex:index withObject:replacementConstraint];
}
maker
- (MASConstraint *)addConstraintWithLayoutAttribute:(NSLayoutAttribute)layoutAttribute {
return [self constraint:nil addConstraintWithLayoutAttribute:layoutAttribute];
}
- (MASConstraint *)addConstraintWithAttributes:(MASAttribute)attrs {
/////
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;
}
- (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 *compositeConstraint = [[MASCompositeConstraint alloc] initWithChildren:children];
compositeConstraint.delegate = self;
[self constraint:constraint shouldBeReplacedWithConstraint:compositeConstraint];
return compositeConstraint;
}
if (!constraint) {
newConstraint.delegate = self;
[self.constraints addObject:newConstraint];
}
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];
}
4、设置布局值
尝试用不支持的值设置布局常量.attempting to set layout constant with unsupported value
NSNumber，CGPoint，CGSize，UIEdgeInsets
尝试添加不支持的属性attempting to add unsupported attribute
UIView、NSValue、MASViewAttribute
offset只是改变约束常量值
equalTo会增加约束关系（secondeViewAttribute），如果是NSValue类型（与offset效果相似），根据约束的布局属性NSLayoutAttribute是否匹配，设置对应的常量值。
//相同
make.left.equalTo(@20);
make.left.offset(20);
//相同
make.left.equalTo(v2.mas_right).offset(20);
make.left.equalTo(v2.mas_right).equalTo(@20);
make.top.inset(0).insets(UIEdgeInsetsZero).offset(0).sizeOffset(CGSizeZero).centerOffset(CGPointZero).valueOffset([NSValue valueWithCGPoint:CGPointZero]).valueOffset( [NSValue value:&CGPointZero withObjCType:@encode(typeof((CGPointZero)))]);
//NSLayoutAttributeTop,NSLayoutAttributeLeft ， 会造成崩溃
Constraint improperly relates anchors of incompatible types
make.top.equalTo(v2.mas_left);//崩溃
make.top.equalTo(@[v2.mas_top,v2.mas_left]);//崩溃
如果是第一个View不是大小约束，且第二个Item是nil，则第二个Item自动设置为第一个View的父View，属性关系与第一个View的属性相同。
+(instancetype)constraintWithItem:(id)view1 attribute:(NSLayoutAttribute)attr1 relatedBy:(NSLayoutRelation)relation toItem:(nullable id)view2 attribute:(NSLayoutAttribute)attr2 multiplier:(CGFloat)multiplier constant:(CGFloat)c;
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