iOS 源代码分析----Masonry

[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);}];

// View+MASAdditions.h
- (NSArray *)mas_makeConstraints:(void(^)(MASConstraintMaker *make))block;

// View+MASAdditions.h
- (NSArray *)mas_updateConstraints:(void(^)(MASConstraintMaker *make))block;- (NSArray *)mas_remakeConstraints:(void(^)(MASConstraintMaker *make))block;

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

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

// MASUtilities.h
#define MAS_VIEW UIView

make.centerX.equalTo(self.view);make.top.equalTo(self.view).with.offset(40);make.width.equalTo(@185);make.height.equalTo(@38);

// MASViewConstraint.m
- (MASConstraint *)left {    return [self addConstraintWithLayoutAttribute:NSLayoutAttributeLeft];}
- (MASConstraint *)addConstraintWithLayoutAttribute:(NSLayoutAttribute)layoutAttribute {    return [self constraint:nil 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]) { ... }    if (!constraint) {        newConstraint.delegate = self;        [self.constraints addObject:newConstraint];    }    return newConstraint;}

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

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

// MASConstraint.m
- (MASConstraint * (^)(id, NSLayoutRelation))equalToWithRelation { MASMethodNotImplemented(); }

// MASConstraint.m
#define MASMethodNotImplemented() \    @throw [NSException exceptionWithName:NSInternalInconsistencyException \                                   reason:[NSString stringWithFormat:@"You must override %@ in a subclass.", NSStringFromSelector(_cmd)] \                                 userInfo:nil]

// MASViewConstraint.m
- (MASConstraint * (^)(id, NSLayoutRelation))equalToWithRelation {    return ^id(id attribute, NSLayoutRelation relation) {        if ([attribute isKindOfClass:NSArray.class]) { ... }        else {            ...            self.layoutRelation = relation;            self.secondViewAttribute = attribute;            return self;        }    };}

// MASConstraintMaker.m
- (void)setSecondViewAttribute:(id)secondViewAttribute {    if ([secondViewAttribute isKindOfClass:NSValue.class]) {        [self setLayoutConstantWithValue:secondViewAttribute];    } else if ([secondViewAttribute isKindOfClass:MAS_VIEW.class]) {        _secondViewAttribute = [[MASViewAttribute alloc] initWithView:secondViewAttribute layoutAttribute:self.firstViewAttribute.layoutAttribute];    } else if ([secondViewAttribute isKindOfClass:MASViewAttribute.class]) {        _secondViewAttribute = secondViewAttribute;    } else {        NSAssert(NO, @"attempting to add unsupported attribute: %@", secondViewAttribute);    }}

make.left.equalTo(@40);

make.left.equalTo(view);

make.left.equalTo(view.mas_right);

// MASConstraintMaker.m
- (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;}

// MASViewConstraint.m
MAS_VIEW *firstLayoutItem = self.firstViewAttribute.view;NSLayoutAttribute firstLayoutAttribute = self.firstViewAttribute.layoutAttribute;MAS_VIEW *secondLayoutItem = self.secondViewAttribute.view;NSLayoutAttribute secondLayoutAttribute = self.secondViewAttribute.layoutAttribute;

// MASViewConstraint.m
if (!self.firstViewAttribute.isSizeAttribute && !self.secondViewAttribute) {   secondLayoutItem = firstLayoutItem.superview;   secondLayoutAttribute = firstLayoutAttribute;}

make.left.equalTo(superView.mas_left).with.offset(10);

// MASViewConstraint.m
MASLayoutConstraint *layoutConstraint   = [MASLayoutConstraint constraintWithItem:firstLayoutItem                                   attribute:firstLayoutAttribute                                   relatedBy:self.layoutRelation                                      toItem:secondLayoutItem                                   attribute:secondLayoutAttribute                                  multiplier:self.layoutMultiplier                                    constant:self.layoutConstant];layoutConstraint.priority = self.layoutPriority;

// View+MASAdditions.m
- (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;}

// MASViewConstraint.m
MASLayoutConstraint *existingConstraint = nil;if (self.updateExisting) {   existingConstraint = [self layoutConstraintSimilarTo:layoutConstraint];}if (existingConstraint) {   // just update the constant   existingConstraint.constant = layoutConstraint.constant;   self.layoutConstraint = existingConstraint;} else {   [self.installedView addConstraint:layoutConstraint];   self.layoutConstraint = layoutConstraint;}
[firstLayoutItem.mas_installedConstraints addObject:self];

[self.installedView addConstraint:layoutConstraint];

// MASConstraint.m- (MASConstraint *)with {    return self;}
- (MASConstraint *)and {    return self;}

// MASViewConstraint.m
- (void)setOffset:(CGFloat)offset {    self.layoutConstant = offset;}

// MASConstraintMaker.m
- (MASConstraint *)edges {    return [self addConstraintWithAttributes:MASAttributeTop | MASAttributeLeft | MASAttributeRight | MASAttributeBottom];}
- (MASConstraint *)size {    return [self addConstraintWithAttributes:MASAttributeWidth | MASAttributeHeight];}
- (MASConstraint *)center {    return [self addConstraintWithAttributes:MASAttributeCenterX | MASAttributeCenterY];}

// MASConstraintMaker.m
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;