做搬运的话哪个网站好,网站模板建站,网上seo研究,中国微电影 网站开发者浅谈 这篇文章是 Masonry 框架源码的解析和笔记。学习Masonry之前#xff0c;先了解这个框架设计的初衷—传统的利用系统API进行纯代码布局的不足。然后#xff0c;根据Masonry常见的几个链式语法中#xff0c;顺藤摸瓜地了解Masonry的调用栈。最后#xff0c;学习并思考这…浅谈 这篇文章是 Masonry 框架源码的解析和笔记。学习Masonry之前先了解这个框架设计的初衷—传统的利用系统API进行纯代码布局的不足。然后根据Masonry常见的几个链式语法中顺藤摸瓜地了解Masonry的调用栈。最后学习并思考这个框架用到的设计模式和链式编程思想。 1. 之前的不足系统API纯代码布局
系统给的自动布局AutoLayout的API
(instancetype)constraintWithItem:(id)view1attribute:(NSLayoutAttribute)attr1relatedBy:(NSLayoutRelation)relationtoItem:(nullable id)view2attribute:(NSLayoutAttribute)attr2multiplier:(CGFloat)multiplierconstant:(CGFloat)c;
传统代码中使用系统API进行布局
- (void)viewDidLoad {[super viewDidLoad];// Do any additional setup after loading the view, typically from a nib.self.view.backgroundColor [UIColor yellowColor];UIView *subView [[UIView alloc] init];subView.backgroundColor [UIColor redColor];// 在设置约束前先将子视图添加进来[self.view addSubview:subView];// 使用autoLayout约束禁止将AutoresizingMask转换为约束[subView setTranslatesAutoresizingMaskIntoConstraints:NO];// 设置subView相对于VIEW的上左下右各40像素NSLayoutConstraint *constraintTop [NSLayoutConstraint constraintWithItem:subView attribute:NSLayoutAttributeTop relatedBy:NSLayoutRelationEqual toItem:self.view attribute:NSLayoutAttributeTop multiplier:1.0 constant:40];NSLayoutConstraint *constraintLeft [NSLayoutConstraint constraintWithItem:subView attribute:NSLayoutAttributeLeft relatedBy:NSLayoutRelationEqual toItem:self.view attribute:NSLayoutAttributeLeft multiplier:1.0 constant:40];// 由于iOS坐标系的原点在左上角所以设置下右边距使用负值NSLayoutConstraint *constraintBottom [NSLayoutConstraint constraintWithItem:subView attribute:NSLayoutAttributeBottom relatedBy:NSLayoutRelationEqual toItem:self.view attribute:NSLayoutAttributeBottom multiplier:1.0 constant:-40];NSLayoutConstraint *constraintRight [NSLayoutConstraint constraintWithItem:subView attribute:NSLayoutAttributeRight relatedBy:NSLayoutRelationEqual toItem:self.view attribute:NSLayoutAttributeRight multiplier:1.0 constant:-40];// 将四条约束加进数组中NSArray *array [NSArray arrayWithObjects:constraintTop, constraintLeft, constraintBottom, constraintRight, nil];// 把约束条件设置到父视图的Contraints中[self.view addConstraints:array];
}
可见系统传统的代码布局有点繁琐。为了简化上述传统布局代码被广泛应用的第三方框架 Masonry 对AutoLayout 进行了封装Swift版则是 SnapKit。这篇文章就是针对 Masonry 源代码的解析与学习笔记。在这之前如下图所示是 Masonry 源代码的结构图
2. 顺藤摸瓜Masonry链式语法的调用栈解析
2.1 mas_makeConstraints外部调用
调用例子
#import Masonry.h[self.containerView addSubview:self.bannerView];
[self.bannerView mas_makeConstraints:^(MASConstraintMaker *make) {make.leading.equalTo(self.containerView.mas_leading);make.top.equalTo(self.containerView.mas_top);make.trailing.equalTo(self.containerView.mas_trailing);make.height.equalTo((kViewWidth(131.0)));
}];
2.2 mas_makeConstraints实现原理通过导入的头文件分析
Masonry.h
#import Foundation/Foundation.h//! Project version number for Masonry.
FOUNDATION_EXPORT double MasonryVersionNumber;//! Project version string for Masonry.
FOUNDATION_EXPORT const unsigned char MasonryVersionString[];#import MASUtilities.h
#import ViewMASAdditions.h
#import ViewMASShorthandAdditions.h
#import ViewControllerMASAdditions.h
#import NSArrayMASAdditions.h
#import NSArrayMASShorthandAdditions.h
#import MASConstraint.h
#import MASCompositeConstraint.h
#import MASViewAttribute.h
#import MASViewConstraint.h
#import MASConstraintMaker.h
#import MASLayoutConstraint.h
#import NSLayoutConstraintMASDebugAdditions.h
其中ViewMASAdditions分类为UIView添加了mas_makeConstraints方法
ViewMASAdditions.m
- (NSArray *)mas_makeConstraints:(void(^)(MASConstraintMaker *))block {self.translatesAutoresizingMaskIntoConstraints NO;MASConstraintMaker *constraintMaker [[MASConstraintMaker alloc] initWithView:self];block(constraintMaker);return [constraintMaker install];
}
ViewMASAdditions.m
- (NSArray *)mas_makeConstraints:(void(^)(MASConstraintMaker *))block {self.translatesAutoresizingMaskIntoConstraints NO;MASConstraintMaker *constraintMaker [[MASConstraintMaker alloc] initWithView:self];block(constraintMaker);return [constraintMaker install];
}
MASConstraintMaker.m
interface MASConstraintMaker () MASConstraintDelegateproperty (nonatomic, weak) MAS_VIEW *view;
property (nonatomic, strong) NSMutableArray *constraints;end
- (id)initWithView:(MAS_VIEW *)view {self [super init];if (!self) return nil;self.view view;self.constraints NSMutableArray.new;return self;
}
2.3 .top通过MASConstraintMaker类源码分析
先分析设置 第一个约束属性 的情况且唯一一个例如
make.top.equalTo(self.containerView.mas_top);2.3.1 MASConstraintMaker的分析
MASConstraintMaker.m
- (MASConstraint *)top {return [self addConstraintWithLayoutAttribute:NSLayoutAttributeTop];
}- (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]) {//replace with composite constraintNSArray *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;
}
该方法返回的newConstraint是一个MASViewConstraint类的示例而MASViewConstraint类又是MASConstraint的子类返回类型写成MASConstraint没毛病。 代码较多暂时可以只先看if (!constraint)里面的代码。可见最后设置 newConstraint对象代理为self (即 MASConstraintMaker)并添加到一开始准备好的 self.constraints 数组中返回。 其中设置 MASViewConstraint 类 newConstraint 对象的 MASConstraintDelegate 代理为self (即 MASConstraintMaker)其作用就是为了能够同时设置多个约束属性即链式语法。
MASConstraintPrivate.h
protocol MASConstraintDelegate NSObject/*** Notifies the delegate when the constraint needs to be replaced with another constraint. For example* A MASViewConstraint may turn into a MASCompositeConstraint when an array is passed to one of the equality blocks*/
- (void)constraint:(MASConstraint *)constraint shouldBeReplacedWithConstraint:(MASConstraint *)replacementConstraint;- (MASConstraint *)constraint:(MASConstraint *)constraint addConstraintWithLayoutAttribute:(NSLayoutAttribute)layoutAttribute;end
2.3.2 MASConstraintMaker的继续分析
第2.3.1节的MASConstraintMaker.m代码中先是初始化了 MASViewAttribute 对象并保存了 view、item以及 NSLayoutAttribute 三个属性。
MASViewAttribute.m
- (id)initWithView:(MAS_VIEW *)view layoutAttribute:(NSLayoutAttribute)layoutAttribute {self [self initWithView:view item:view layoutAttribute:layoutAttribute];return self;
}- (id)initWithView:(MAS_VIEW *)view item:(id)item layoutAttribute:(NSLayoutAttribute)layoutAttribute {self [super init];if (!self) return nil;_view view;_item item;_layoutAttribute layoutAttribute;return self;
}
然后又初始化了 MASViewConstraint 对象内部配置了些默认参数并保存了如上的第一个约束参数 MASViewAttribute。
MASViewConstraint.m
- (id)initWithFirstViewAttribute:(MASViewAttribute *)firstViewAttribute {self [super init];if (!self) return nil;_firstViewAttribute firstViewAttribute;self.layoutPriority MASLayoutPriorityRequired;self.layoutMultiplier 1;return self;
}
2.4 .equalTo 通过基类MASConstraint及其子类MASViewConstraint分析
第一个约束属性 设置完后走到.equalTo时前面返回已经是一个 MASViewConstraint(继承自MASConstraint) 对象了因而调用的是在基类MASConstraint中声明并实现的block属性getter方法。
MASConstraint.m
- (MASConstraint * (^)(id))equalTo {return ^id(id attribute) {return self.equalToWithRelation(attribute, NSLayoutRelationEqual);};
}
其中基类 MASConstraint 仅仅声明并没有实现equalToWithRelation抽象方法。但是如2.3节中的链式语法.top该方法返回的newConstraint实际是其子类–MASViewConstraint类的实例故而可调用子类MASViewConstraint实现的equalToWithRelation方法
MASViewConstraint.m
- (MASConstraint * (^)(id, NSLayoutRelation))equalToWithRelation {return ^id(id attribute, NSLayoutRelation relation) {if ([attribute isKindOfClass:NSArray.class]) {NSAssert(!self.hasLayoutRelation, Redefinition of constraint relation);NSMutableArray *children NSMutableArray.new;for (id attr in attribute) {MASViewConstraint *viewConstraint [self copy];viewConstraint.layoutRelation relation;viewConstraint.secondViewAttribute attr;[children addObject:viewConstraint];}MASCompositeConstraint *compositeConstraint [[MASCompositeConstraint alloc] initWithChildren:children];compositeConstraint.delegate self.delegate;[self.delegate constraint:self shouldBeReplacedWithConstraint:compositeConstraint];return compositeConstraint;} else {NSAssert(!self.hasLayoutRelation || self.layoutRelation relation [attribute isKindOfClass:NSValue.class], Redefinition of constraint relation);self.layoutRelation relation;self.secondViewAttribute attribute;return self;}};
}
代码较多暂时可先看else {里面的代码。
(1) self.layoutRelation relation;
首先是 self.layoutRelation 保存了约束关系且重写了 set 方法在里面用 self.hasLayoutRelation 这个 BOOL 标识已经有约束关系。
MASViewConstraint.m
- (void)setLayoutRelation:(NSLayoutRelation)layoutRelation {_layoutRelation layoutRelation;self.hasLayoutRelation YES;
}
(2) self.secondViewAttribute attribute;
然后同样是重写了 self.secondViewAttribute 的 set 方法这里会根据不同的情况做不同的操作。
- (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]) {MASViewAttribute *attr secondViewAttribute;if (attr.layoutAttribute NSLayoutAttributeNotAnAttribute) {_secondViewAttribute [[MASViewAttribute alloc] initWithView:attr.view item:attr.item layoutAttribute:self.firstViewAttribute.layoutAttribute];;} else {_secondViewAttribute secondViewAttribute;}} else {NSAssert(NO, attempting to add unsupported attribute: %, secondViewAttribute);}
}其中第1种情况对应的是
make.height.equalTo(20.0f)传入 NSValue 的时, 会直接设置 constraint 的 offset, centerOffset, sizeOffset, 或者 insets。调用栈如下
//MASViewConstraint.m
if ([secondViewAttribute isKindOfClass:NSValue.class]) {[self setLayoutConstantWithValue:secondViewAttribute];
}
//MASConstraint.m
- (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);}
}
//MASViewConstraint.m
- (void)setOffset:(CGFloat)offset {self.layoutConstant offset;
}
//MASViewConstraint.m
- (void)setLayoutConstant:(CGFloat)layoutConstant {_layoutConstant layoutConstant;
#if TARGET_OS_MAC !(TARGET_OS_IPHONE || TARGET_OS_TV)if (self.useAnimator) {[self.layoutConstraint.animator setConstant:layoutConstant];} else {self.layoutConstraint.constant layoutConstant;}
#elseself.layoutConstraint.constant layoutConstant;
#endif
}第2种情况一般是直接传入一个视图
make.top.equalTo(self)这时, 就会初始化一个 layoutAttribute 属性与 firstViewArribute 相同的 MASViewAttribute, 上面的代码就会使视图与 view 顶部对齐。
第3种情况会传入一个视图的 MASViewAttribute:
make.top.equalTo(view.mas_bottom);使用这种写法时, 一般是因为约束的方向不同. 这行代码会使视图的顶部与 view 的底部对齐。
2.5 .height.widthMasonry的链式语法特性
调用例子
make.height.width.equalTo(20);其中.height 设置第一个约束属性时调用的是 MASConstraintMaker.m 中的 .height addConstraintWithLayoutAttribute以及- (MASConstraint *)constraint:(MASConstraint *)constraint addConstraintWithLayoutAttribute:(NSLayoutAttribute)layoutAttribute。
MASConstraintMaker.m
- (MASConstraint *)height {return [self addConstraintWithLayoutAttribute:NSLayoutAttributeHeight];
}- (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]) {//replace with composite constraintNSArray *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;
}
该方法调用栈返回的是一个MASViewConstraint(父类是 MASConstraint) 对象。 因此通过 .width 设置第二个约束属性的时候调用的先是基类 MASConstraint.m 中的.width然后调用由子类MASViewConstraint实现的addConstraintWithLayoutAttribute方法。这时候的调用栈为
MASConstraint.m
- (MASConstraint *)width {return [self addConstraintWithLayoutAttribute:NSLayoutAttributeWidth];
}- (MASConstraint *)addConstraintWithLayoutAttribute:(NSLayoutAttribute __unused)layoutAttribute {MASMethodNotImplemented();
}
MASViewConstraint.m
- (MASConstraint *)addConstraintWithLayoutAttribute:(NSLayoutAttribute)layoutAttribute {NSAssert(!self.hasLayoutRelation, Attributes should be chained before defining the constraint relation);return [self.delegate constraint:self addConstraintWithLayoutAttribute:layoutAttribute];
}
这其中self.delegate 是什么呢如2.3.1节所述MASConstraintMaker.m 中设置了 MASViewConstraint 类 newConstraint 对象的 MASConstraintDelegate 代理为“self” (即 MASConstraintMaker)其作用就是为了能够同时设置多个约束属性即链式语法。所以第二个设置约束属性跟第一个设置约束属性最终 调用的方法一样都是MASConstraintMaker.m中实现的addConstraintWithLayoutAttribute。
MASConstraintMaker.m
- (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 constraintNSArray *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;
}
当设置 第二次约束属性 并执行完之后我们还可以发现 constraint 不为 nil而是一个 MASViewConstraint 对象 所以该方法调用栈返回的不是 MASViewConstraint 对象而是 MASCompositeConstraint 这个对象了下面我们来看看这个类。
2.6 约束的集合 MASCompositeConstraint
MASCompositeConstraint 是约束的集合它里面有个私有的数组用来存放多个 MASViewAttribute 对象。
make.height.width.equalTo(20)
当设置 第二个约束属性走到 .width 时最终走的是
MASConstraintMaker.m
- (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 constraintNSArray *children [constraint, newConstraint];MASCompositeConstraint *compositeConstraint [[MASCompositeConstraint alloc] initWithChildren:children];compositeConstraint.delegate self;[self constraint:constraint shouldBeReplacedWithConstraint:compositeConstraint];return compositeConstraint;}....
}
其中可以成功的走进 if判读里面将 .height .wight 两条约束 MASViewConstraint对象塞到数组里创建 MASCompositeConstraint 对象并且同样设置了 delegate最后还把 self.constraints 里面事先添加好的约束 MASViewConstraint 对象替换成了 MASCompositeConstraint 对象。
#pragma mark - MASConstraintDelegate- (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];
}
另外我们可以点击 MASCompositeConstraint 初始化方法里看看它内部会通过 for 循环把数组里面的所有 MASViewConstraint 对象同样设置了 delegate
- (id)initWithChildren:(NSArray *)children {self [super init];if (!self) return nil;_childConstraints [children mutableCopy];for (MASConstraint *constraint in _childConstraints) {constraint.delegate self;}return self;
}
这么做的目的同时是为了能够继续链式调用比如我们再设置第三个约束属性 .left
make.height.width.left.equalTo(20);这时候的调用栈如下
MASConstraint.m
- (MASConstraint *)left {return [self addConstraintWithLayoutAttribute:NSLayoutAttributeLeft];
}MASCompositeConstraint.m
- (MASConstraint *)addConstraintWithLayoutAttribute:(NSLayoutAttribute)layoutAttribute {[self constraint:self addConstraintWithLayoutAttribute:layoutAttribute];return self;
}- (MASConstraint *)constraint:(MASConstraint __unused *)constraint addConstraintWithLayoutAttribute:(NSLayoutAttribute)layoutAttribute {idMASConstraintDelegate strongDelegate self.delegate;MASConstraint *newConstraint [strongDelegate constraint:self addConstraintWithLayoutAttribute:layoutAttribute];newConstraint.delegate self;[self.childConstraints addObject:newConstraint];return newConstraint;
}可以发现这里又是通过 delegate 方式调用 MASConstraintMaker 工厂类中的
MASConstraintMaker.m
- (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 constraintNSArray *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;
}此时注意到两个 if 体都没有走进去既不像第一次也不像第二次约束设置的时候。所以这次仅仅是初始化了个 MASViewConstraint 对象就直接返回了然后回到上个方法中添加到 MASCompositeConstraint 的私有数组 self.childConstraints 中返回备用。 关于三次 约束设置之后的 .equalTo(20)因为执行完 .left 时返回的是 MASCompositeConstraint 对象到这一步的时候会有点变化调用栈如下
MASConstraint.m
- (MASConstraint * (^)(id))equalTo {return ^id(id attribute) {return self.equalToWithRelation(attribute, NSLayoutRelationEqual);};
}MASCompositeConstraint.m
- (MASConstraint * (^)(id, NSLayoutRelation))equalToWithRelation {return ^id(id attr, NSLayoutRelation relation) {for (MASConstraint *constraint in self.childConstraints.copy) {constraint.equalToWithRelation(attr, relation);}return self;};
}可以发现这里会循环之前准备好的私有数组 self.childConstraints调用 MASViewConstraint.m 的 equalToWithRelation 方法和上面讲的一样了。
2.7 添加约束到视图
mas_makeConstraints 方法的最后会调用 [constraintMaker install] 方法来添加所有存储在 self.constraints 数组中的所有约束。
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;
}(1). 如果需要重新构建约束也就是 调用 mas_remakeConstraints:方法会先取出视图的所有约束然后通过一个 for 循环调用 uninstall 来清空所有约束 (2). 如果不需要重新构建约束会取出 self.constraints 数组中准备好的约束通过 for 循环调用 install 来把约束添加到视图上。 关于 install 是基类 MASConstraint 的抽象方法方法体由MASViewConstraint 或 MASCompositeConstraint 实现。而 MASCompositeConstraint 的 install方法体中其实也是调用的由MASViewConstraint类实现的install。
MASConstraint.m
- (void)install { MASMethodNotImplemented(); }MASCompositeConstraint.m
- (void)install {for (MASConstraint *constraint in self.childConstraints) {constraint.updateExisting self.updateExisting;[constraint install];}
}MASViewConstraint.m 这里代码较多就不分开解析了直接分为7步写到源码的注释中如下所示
- (void)install {//【1】如果约束以及存在并是 active 会直接返回。if (self.hasBeenInstalled) {return;}//【2】如果 self.layoutConstraint 响应了 isActive 方法并且不为空会激活这条约束并添加到 mas_installedConstraints 数组中最后返回。if ([self supportsActiveProperty] self.layoutConstraint) {self.layoutConstraint.active YES;[self.firstViewAttribute.view.mas_installedConstraints addObject:self];return;}//【3】这边是获取即将用于初始化 NSLayoutConstraint 的子类 MASLayoutConstraint 的几个属性。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)//【4】这边是判断当前即将添加的约束是否是 size 类型的并且 self.secondViewAttribute 也就是约束的第二个参数是 nileg make.left.equalTo(10)会自动将约束添加到约束的第一个参数视图的 superview 上。if (!self.firstViewAttribute.isSizeAttribute !self.secondViewAttribute) {secondLayoutItem self.firstViewAttribute.view.superview;secondLayoutAttribute firstLayoutAttribute;}//【5】然后就会初始化 NSLayoutConstraint 的子类 MASLayoutConstraint。MASLayoutConstraint *layoutConstraint [MASLayoutConstraint constraintWithItem:firstLayoutItemattribute:firstLayoutAttributerelatedBy:self.layoutRelationtoItem:secondLayoutItemattribute:secondLayoutAttributemultiplier:self.layoutMultiplierconstant:self.layoutConstant];layoutConstraint.priority self.layoutPriority;layoutConstraint.mas_key self.mas_key;//【6】这段代码会先判断是否有约束第二个参数的视图有的话会寻找约束第一个和第二参数视图的公共 Superview相当于求两个数的最小公倍数如果不满足第一个条件会判断约束第一个参数是否是 size 类型的是的话直接取到它的视图最后都不满足会直接取到约束第一个参数视图父视图。if (self.secondViewAttribute.view) {MAS_VIEW *closestCommonSuperview [self.firstViewAttribute.view mas_closestCommonSuperview:self.secondViewAttribute.view];NSAssert(closestCommonSuperview,couldnt find a common superview for % and %,self.firstViewAttribute.view, self.secondViewAttribute.view);self.installedView closestCommonSuperview;} else if (self.firstViewAttribute.isSizeAttribute) {self.installedView self.firstViewAttribute.view;} else {self.installedView self.firstViewAttribute.view.superview;}//【7】如果需要升级当前的约束就会获取原有的约束并替换为新的约束这样就不需要再次为 view 安装约束。如果原来的 view 中不存在可以升级的约束那么就会在上一步寻找到的 installedView 上面添加约束。MASLayoutConstraint *existingConstraint nil;if (self.updateExisting) {existingConstraint [self layoutConstraintSimilarTo:layoutConstraint];}if (existingConstraint) {// just update the constantexistingConstraint.constant layoutConstraint.constant;self.layoutConstraint existingConstraint;} else {[self.installedView addConstraint:layoutConstraint];self.layoutConstraint layoutConstraint;[firstLayoutItem.mas_installedConstraints addObject:self];}
}其中第【6】步中的mas_closestCommonSuperview方法它会寻找 firstLayoutItem 和 secondLayoutItem 两个视图的公共 superview, 相当于求两个数的最小公倍数.
ViewMASAdditions.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;
}
3. 顺藤再摸瓜Masonry其它链式语法的调用栈解析选读
3.1 make.edges.equalTo(view)
make.edges.equalTo(view)
我们再来看看这种写法调用栈如下
MASConstraintMaker.m
- (MASConstraint *)edges {return [self addConstraintWithAttributes:MASAttributeTop | MASAttributeLeft | MASAttributeRight | MASAttributeBottom];
}
- (MASConstraint *)addConstraintWithAttributes:(MASAttribute)attrs {__unused MASAttribute anyAttribute (MASAttributeLeft | MASAttributeRight | MASAttributeTop | MASAttributeBottom | MASAttributeLeading| MASAttributeTrailing | MASAttributeWidth | MASAttributeHeight | MASAttributeCenterX| MASAttributeCenterY | ......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];...... 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;
}代码太多省略了一部分可以发现这段代码作用就是返回一个包含多条约束的 MASCompositeConstraint 对象接着后面的操作也都是一样的了。
3.2 make.edges.equalTo(UIEdgeInsetsMake(0.0f, 0.0f, 0.0f, 0.0f));
上面3.1中例子的写法还可以改成这样
make.edges.equalTo(UIEdgeInsetsMake(0.0f, 0.0f, 0.0f, 0.0f));这里的 equalTo 需要注意下它是一个宏定义在 MASConstraint.h 中
MASConstraint.h
#define mas_equalTo(...) equalTo(MASBoxValue((__VA_ARGS__)))
#define mas_greaterThanOrEqualTo(...) greaterThanOrEqualTo(MASBoxValue((__VA_ARGS__)))
#define mas_lessThanOrEqualTo(...) lessThanOrEqualTo(MASBoxValue((__VA_ARGS__)))
#define mas_offset(...) valueOffset(MASBoxValue((__VA_ARGS__)))
#ifdef MAS_SHORTHAND_GLOBALS
#define equalTo(...) mas_equalTo(__VA_ARGS__)
#define greaterThanOrEqualTo(...) mas_greaterThanOrEqualTo(__VA_ARGS__)
#define lessThanOrEqualTo(...) mas_lessThanOrEqualTo(__VA_ARGS__)
#define offset(...) mas_offset(__VA_ARGS__)代入上述宏定义前面的代码等效成
make.edges.equalTo(MASBoxValue(UIEdgeInsetsMake(0.0f, 0.0f, 0.0f, 0.0f)));可以发现其实里面调用的是 MASBoxValue 这个宏它将 C 和 Objective-C 语言中的一些基本数据结构比如说 double CGPoint CGSize 这些值用 NSValue 进行包装。 这里还支持直接调用 size、center 等具体实现都差不多就不熬述了
make.center.equalTo(CGPointMake(0, 50));
make.size.equalTo(CGSizeMake(200, 100));3.3 make.height.equalTo([redView, blueView])
make.height.equalTo([redView, blueView])再来看看这种传数组的在走到 .equalTo 时最终会调用 MASViewConstraint.m 里面的 equalToWithRelation 方法
MASConstraint.m
- (MASConstraint * (^)(id))equalTo {return ^id(id attribute) {return self.equalToWithRelation(attribute, NSLayoutRelationEqual);};
}MASViewConstraint.m
- (MASConstraint * (^)(id, NSLayoutRelation))equalToWithRelation {return ^id(id attribute, NSLayoutRelation relation) {if ([attribute isKindOfClass:NSArray.class]) {NSAssert(!self.hasLayoutRelation, Redefinition of constraint relation);NSMutableArray *children NSMutableArray.new;for (id attr in attribute) {MASViewConstraint *viewConstraint [self copy];viewConstraint.layoutRelation relation;viewConstraint.secondViewAttribute attr;[children addObject:viewConstraint];}MASCompositeConstraint *compositeConstraint [[MASCompositeConstraint alloc] initWithChildren:children];compositeConstraint.delegate self.delegate;[self.delegate constraint:self shouldBeReplacedWithConstraint:compositeConstraint];return compositeConstraint;} else { .... }};
}这边还是遍历数组并且 MASViewConstraint 实现 NSCopying 协议调用 [self copy] 会创建 MASViewConstraint 对象
- (id)copyWithZone:(NSZone __unused *)zone {MASViewConstraint *constraint [[MASViewConstraint alloc] initWithFirstViewAttribute:self.firstViewAttribute];constraint.layoutConstant self.layoutConstant;constraint.layoutRelation self.layoutRelation;constraint.layoutPriority self.layoutPriority;constraint.layoutMultiplier self.layoutMultiplier;constraint.delegate self.delegate;return constraint;
}然后会根据传的数组里面的 Value 类型来做不同的操作前面讲过就不熬述了
- (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);}
}最后便是生成 MASCompositeConstraint 对象并通过 delegate 方式调用 MASConstraintMaker 的方法替换 self.constraints 数组里的约束
- (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. 举一反三框架源码的学习启示
4.1 简化的设计模式工厂类工厂方法
MASConstraintMaker类就是一个工厂类负责创建MASConstraint类型的对象依赖于MASConstraint接口而不依赖于具体实现。在UIView的ViewMASAdditions分类中就是调用的MASConstraintMaker类中的一些方法。上述我们在使用Masonry给subView添加约束时mas_makeConstraints方法中的Block的参数就是MASConstraintMaker的对象。用户可以通过该Block回调过来的MASConstraintMaker对象给View指定要添加的约束以及该约束的值。该工厂中的constraints属性数组就记录了该工厂创建的所有MASConstraint对象。 MASConstraintMaker 之所以成为约束工厂类因为MASConstraintMaker赋值创建NSLayoutConstraint对象因为Masonry将NSLayoutConstraint类进一步封装成了MASViewConstraint所以MASConstraintMaker是负责创建MASViewConstraint的对象并调用MASViewConstraint对象的Install方法将该约束添加到相应的视图中。 说了这么多总结一下如果你调用maker.top, maker.left等等这些方法都会调用下方的工厂方法来创建相应的MASViewConstraint对象并记录在工厂对象的约束数组中。之所以能链式调用就是讲当前的工厂对象MASConstraintMaker指定为MASViewConstraint对象的代理所以一个MASViewConstraint对象就可以通过代理来调用工厂方法来创建另一个新的MASViewConstraint对象了此处用到了代理模式。
ClientUIView通过分类ViewMASAdditions来扮演工厂类MASConstraintMaker抽象产品MASConstraint具体产品MASViewConstraint MASCompositeConstraint
4.2 真正的设计模式组合模式
换一种角度看Masonry 并非单纯的工厂模式而是采用了经典的 Composite 设计模式可译作组合模式。
4.2.1 经典 组合模式 中的参与者
Client
通过 Component 接口操纵组合部件的对象。 Component为组合中的对象声明接口。在适当的情况下实现所有类共有接口的缺省行为声明一个接口用于访问和管理 Component 的子组件。在递归结构中定义一个接口用于访问一个父部件并在合适的情况下实现它。 Leaf在组合中表示叶节点对象叶节点没有子节点。在组合中定义图元对象的行为。 Composite定义有子部件的那些部件的行为。在 Composite 接口中实现与子部件有关的操作。
4.2.2 从 组合模式 的角度看Masonry 框架中的角色分析
UIView通过分类ViewMASAdditions来调用Masonry Client
MASConstraintMaker ComponentMASConstraint LeafMASViewConstraint CompositeMASCompositeConstraint
4.3 编程思想链式编程
Objective-C是一门动态语言它使用了一种动态的消息发送机制即对象(object)或类(class)调用方法。而OC中的点语法则只能通过setter和getter方法作用于类的属性而不能作用于某个方法。想实现链式语法只能通过类似block属性的getter方法。
链式编程思想核心思想为将block作为方法的返回值且返回值的类型为调用者本身并将该方法以setter的形式返回这样就可以实现了连续调用即为链式编程。
