Masonry研究3 MASConstraintMaker

MASConstraintMaker

---

• 涉及的类有MASConstraint，包含持有的具体数据
• 创建maker的方法,这个方法是把View用weak持有，并创建一个保存所有设置MASConstraint的一个数组

@interface MASConstraintMaker () 

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

@end

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

• 设置约束的第一二步就是设置top、left等属性，代码逻辑如下

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

通过NSLayoutAttribute创建一个MASConstraint并将创建的约束加入到数组constraints中，如果设置的是size、center等复合型的约束，则创建包含多个子约束的MASCompositeConstraint

- (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;
}

在将设置好添加到constraints数组中的约束都设置好后就要开始把约束加到View上起作用，方法为install,逻辑如下：

• 如果是remake，也就是removeExisting =YES时，将已经添加上的约束全部uninstall，
• 把本次maker里的所有创建的contraint设置好updateExisting,然后一个一个的install

- (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;
}