使用Block实现KVO.doc

使用Block实现KVOSJKVOController的用法只需要引入NSObject+SJKVOController.h头文件就可以使用SJKVOController。 先看一下它的头文件：#import #import SJKVOHeader.hinterface NSObject (SJKVOController)/= add observer =/- (void)sj_addObserver:(NSObject *)observer forKeys:(NSArray *)keys withBlock:(SJKVOBlock)block;- (void)sj_addObserver:(NSObject *)observer forKey:(NSString *)key withBlock:(SJKVOBlock)block;/= remove observer =/- (void)sj_removeObserver:(NSObject *)observer forKeys:(NSArray *)keys;- (void)sj_removeObserver:(NSObject *)observer forKey:(NSString *)key;- (void)sj_removeObserver:(NSObject *)observer;- (void)sj_removeAllObservers;/= list observers =/- (void)sj_listAllObservers;end从上面的API可以看出，这个小轮子： 1. 支持一次观察同一对象的多个属性。 2. 可以一次只观察一个对象的一个属性。 3. 可以移除对某个对象对多个属性的观察。 4. 可以移除对某个对象对某个属性的观察。 5. 可以移除某个观察自己的对象。 6. 可以移除所有观察自己的对象。 6. 打印出所有观察自己的对象的信息，包括对象本身，观察的属性，setter方法。下面来结合Demo讲解一下如何使用这个小轮子：在点击上面两个按钮中的任意一个，增加观察：一次性添加：- (IBAction)addObserversTogether:(UIButton *)sender NSArray *keys = number,color; self.model sj_addObserver:self forKeys:keys withBlock:(id observedObject, NSString *key, id oldValue, id newValue) if (key isEqualToString:number) dispatch_async(dispatch_get_main_queue(), self.numberLabel.text = NSString stringWithFormat:%,newValue; ); else if (key isEqualToString:color) dispatch_async(dispatch_get_main_queue(), self.numberLabel.backgroundColor = newValue; ); ;分两次添加：- (IBAction)addObserverSeparatedly:(UIButton *)sender self.model sj_addObserver:self forKey:number withBlock:(id observedObject, NSString *key, id oldValue, id newValue) dispatch_async(dispatch_get_main_queue(), self.numberLabel.text = NSString stringWithFormat:%,newValue; ); ; self.model sj_addObserver:self forKey:color withBlock:(id observedObject, NSString *key, id oldValue, id newValue) dispatch_async(dispatch_get_main_queue(), self.numberLabel.backgroundColor = newValue; ); ;添加以后，点击最下面的按钮来显示所有的观察信息：- (IBAction)showAllObservingItems:(UIButton *)sender self.model sj_listAllObservers;输出：SJKVOController80499:4242749 SJKVOLog:= Start Listing All Observers: = SJKVOController80499:4242749 SJKVOLog:observer item:observer: | key: color | setter: setColor:SJKVOController80499:4242749 SJKVOLog:observer item:observer: | key: number | setter: setNumber:在这里我重写了description方法，打印出了每个观察的对象和key,以及setter方法。现在点击更新按钮，则会更新model的number和color属性，从而触发KVO：- (IBAction)updateNumber:(UIButton *)sender /trigger KVO : number NSInteger newNumber = arc4random() % 100; self.model.number = NSNumber numberWithInteger:newNumber; /trigger KVO : color NSArray *colors = UIColor redColor,UIColor yellowColor,UIColor blueColor,UIColor greenColor; NSInteger colorIndex = arc4random() % 3; self.model.color = colorscolorIndex;我们可以看到中间的Label上面显示的数字和背景色都在变化，成功实现了KVO：现在我们移除观察，点击remove按钮- (IBAction)removeAllObservingItems:(UIButton *)sender self.model sj_removeAllObservers; 在移除了所有的观察者以后，则会打印出：SJKVOController80499:4242749 SJKVOLog:Removed all obserbing objects of object:而且如果在这个时候打印观察者list，则会输出：SJKVOController80499:4242749 SJKVOLog:There is no observers obserbing object:需要注意的是，这里的移除可以有多种选择：可以移某个对象的某个key，也可以移除某个对象的几个keys，为了验证，我们可以结合list方法来验证一下移除是否成功：验证1:在添加number和color的观察后，移除nunber的观察：- (IBAction)removeAllObservingItems:(UIButton *)sender self.model sj_removeObserver:self forKey:number;在移除以后，我们调用list方法，输出：SJKVOController80850:4278383 SJKVOLog:= Start Listing All Observers: =SJKVOController80850:4278383 SJKVOLog:observer item:observer: | key: color | setter: setColor:现在只有color属性被观察了。看一下实际的效果：我们可以看到，现在只有color在变，而数字没有变化了，验证此移除方法正确。验证2:在添加number和color的观察后，移除nunber和color的观察：- (IBAction)removeAllObservingItems:(UIButton *)sender self.model sj_removeObserver:self forKeys:number,color;在移除以后，我们调用list方法，输出：SJKVOController80901:4283311 SJKVOLog:There is no observers obserbing object:现在color和number属性都不被观察了。看一下实际的效果：我们可以看到，现在color和number都不变了，验证此移除方法正确。OK，现在知道了怎么用SJKVOController，我下面给大家看一下代码：SJKVOController代码解析先大致讲解一下SJKVOController的实现思路： 1. 为了减少侵入性，SJKVOController被设计为NSObject的一个分类。 2. SJKVOController仿照了KVO的实现思路，在添加观察以后在运行时动态生成当前类的子类，给这个子类添加被观察的属性的set方法并使用isa swizzle的方式将当前对象转换为当前类的子类的实现。 3. 同时，这个子类还使用了关联对象来保存一个“观察项”的set，每一个观察项封装了一次观察的行为（有去重机制）：包括观察自己的对象，自己被观察的属性，以及传进来的block。 4. 在当前类，也就是子类的set方法被调用的时候做三件事情： - 第一件事情是使用KVC来找出当前属性的旧值。 - 第二件事情是调用父类（原来的类）的set方法（设新值）。 - 第三件事是根据当前的观察对象和key，在观察项set里面找出对应的block并调用。再来看一下这个小轮子的几个类：SJKVOController：实现KVO主要功能的类。SJKVOObserverItem：封装观察项的类。SJKVOTool：setter和getter的相互转换和相关运行时查询方法等。SJKVOError：封装错误类型。SJKVOHeader：引用了运行时的头文件。下面开始一个一个来讲解每个类的源码：SJKVOController再看一下头文件：#import #import SJKVOHeader.hinterface NSObject (SJKVOController)/= add observer =/- (void)sj_addObserver:(NSObject *)observer forKeys:(NSArray *)keys withBlock:(SJKVOBlock)block;- (void)sj_addObserver:(NSObject *)observer forKey:(NSString *)key withBlock:(SJKVOBlock)block;/= remove observer =/- (void)sj_removeObserver:(NSObject *)observer forKeys:(NSArray *)keys;- (void)sj_removeObserver:(NSObject *)observer forKey:(NSString *)key;- (void)sj_removeObserver:(NSObject *)observer;- (void)sj_removeAllObservers;/= list observers =/- (void)sj_listAllObservers;end每个方法的意思相信读者已经能看懂了，现在讲一下具体的实现。从sj_addObserver:forKey withBlock:开始：sj_addObserver:forKey withBlock:方法：除去一些错误的判断，该方法作了下面几件事情：1.判断当前被观察的类是否存在与传入key对应的setter方法：SEL setterSelector = NSSelectorFromString(SJKVOTool setterFromGetter:key);Method setterMethod = SJKVOTool objc_methodFromClass:self class selector:setterSelector;/error: no corresponding setter mothodif (!setterMethod) SJLog(%,SJKVOError errorNoMatchingSetterForKey:key); return;2. 如果有，判断当前被观察到类是否已经是KVO类(在KVO机制中，如果某个对象一旦被观察，则这个对象就变成了带有包含KVO前缀的类的实例)。如果已经是KVO类，则将当前实例的isa指针指向其父类（最开始被观察的类）： /get original class(current class,may be KVO class) NSString *originalClassName = NSStringFromClass(OriginalClass); /如果当前的类是带有KVO前缀的类(也就是已经被观察到类),则需要将KVO前缀的类删除，并讲 if (originalClassName hasPrefix:SJKVOClassPrefix) /now,the OriginalClass is KVO class, we should destroy it and make new one Class CurrentKVOClass = OriginalClass; object_setClass(self, class_getSuperclass(OriginalClass); objc_disposeClassPair(CurrentKVOClass); originalClassName=originalClassName substringFromIndex:(SJKVOClassPrefix.length); 3. 如果不是KVO类（说明当前实例没有被观察），则创建一个带有KVO前缀的类，并将当前实例的isa指针指向这个新建的类： /create a KVO class Class KVOClass = self createKVOClassFromOriginalClassName:originalClassName; /swizzle isa from self to KVO class object_setClass(self, KVOClass);看一下如何新建一个新的类：- (Class)createKVOClassFromOriginalClassName:(NSString *)originalClassName NSString *kvoClassName = SJKVOClassPrefix stringByAppendingString:originalClassName; Class KVOClass = NSClassFromString(kvoClassName); / KVO class already exists if (KVOClass) return KVOClass; / if there is no KVO class, then create one KVOClass = objc_allocateClassPair(OriginalClass, kvoClassName.UTF8String, 0);/OriginalClass is super class / pretending to be the original class:return the super class in class method Method clazzMethod = class_getInstanceMethod(OriginalClass, selector(class); class_addMethod(KVOClass, selector(class), (IMP)return_original_class, method_getTypeEncoding(clazzMethod); / finally, register this new KVO class objc_registerClassPair(KVOClass); return KVOClass;4. 查看观察项set，如果这个set里面有已经保存的观察项，则需要新建一个空的观察项set，将已经保存的观察项放入这个新建的set里面： /if we already have some history observer items, we should add them into new KVO class NSMutableSet* observers = objc_getAssociatedObject(self, &SJKVOObservers); if (observers.count 0) NSMutableSet *newObservers = NSMutableSet alloc initWithCapacity:5; objc_setAssociatedObject(self, &SJKVOObservers, newObservers, OBJC_ASSOCIATION_RETAIN_NONATOMIC); for (SJKVOObserverItem *item in observers) self KVOConfigurationWithObserver:item.observer key:item.key block:item.block kvoClass:KVOClass setterSelector:item.setterSelector setterMethod:setterMethod; 看一下如何保存观察项的：- (void)KVOConfigurationWithObserver:(NSObject *)observer key:(NSString *)key block:(SJKVOBlock)block kvoClass:(Class)kvoClass setterSelector:(SEL)setterSelector setterMethod:(Method)setterMethod /add setter method in KVO Class if(!SJKVOTool detectClass:OriginalClass hasSelector:setterSelector) class_addMethod(kvoClass, setterSelector, (IMP)kvo_setter_implementation, method_getTypeEncoding(setterMethod); /add item of this observer&key pair self addObserverItem:observer key:key setterSelector:setterSelector setterMethod:setterMethod block:block;这里首先给KVO类增加了setter方法：/implementation of KVO setter methodvoid kvo_setter_implementation(id self, SEL _cmd, id newValue) NSString *setterName = NSStringFromSelector(_cmd); NSString *getterName = SJKVOTool getterFromSetter:setterName; if (!getterName) SJLog(%,SJKVOError errorTransferSetterToGetterFaildedWithSetterName:setterName); return; / create a super class of a specific instance Class superclass = class_getSuperclass(OriginalClass); struct objc_super superclass_to_call = .super_class = superclass, /super class .receiver = self, /insatance of this class ; / cast method pointer void (*objc_msgSendSuperCasted)(void *, SEL, id) = (void *)objc_msgSendSuper; / call supers setter, the supper is the original class objc_msgSendSuperCasted(&superclass_to_call, _cmd, newValue); / look up observers and call the blocks NSMutableSet *observers = objc_getAssociatedObject(self,&SJKVOObservers); if (observers.count 0) for (SJKVOObserverItem *item in observers) if ( (item.observer = observer) & item.key isEqualToString:key) findSameObserverAndKey = YES; if (!findSameObserverAndKey) self KVOConfigurationWithObserver:observer key:key block:block kvoClass:KVOClass setterSelector:setterSelector setterMethod:setterMethod; 而一次性添加多个key的方法，也只是调用多次一次性添加单个key的方法罢了：- (void)sj_addObserver:(NSObject *)observer forKeys:(NSArray *)keys withBlock:(SJKVOBlock)block /error: keys array is nil or no elements if (keys.count = 0) SJLog(%,SJKVOError errorInvalidInputObservingKeys); return; /one key corresponding to one specific item, not the observer keys enumerateObjectsUsingBlock:(NSString * key, NSUInteger idx, BOOL * _Nonnull stop) self sj_addObserver:observer forKey:key withBlock:block; ;关于移除观察的实现，只是在观察项set里面找出封装了对应的观察对象和key的观察项就可以了：- (void)sj_removeObserver:(NSObject *)observer forKey:(NSString *)key NSMutableSet* observers = objc_getAssociatedObject(self, &SJKVOObservers); if (observers.count 0) SJKVOObserverItem *removingItem = nil; for (SJKVOObserverItem* item in observers) if (item.observer = observer & item.key isEqualToString:key) removingItem = item; break; if (removingItem) observers removeObject:removingItem; 再看一下移除所有观察者：- (void)sj_removeAllObservers NSMutableSet* observers = objc_getAssociatedObject(self, &SJKVOObservers); if (observers.count 0) observers removeAllObjects; SJLog(SJKVOLog:Removed all obserbing objects of object:%,self); else SJLog(SJKVOLog:There is no observers obserbing object:%,self); SJKVOObserverItem这个类负责封装每一个观察项的信息，包括： - 观察者对象。 - 被观察的key。 - setter方法名（SEL） - setter方法（Method） - 回调的block需要注意的是: 在这个小轮子里，对于同一个对象可以观察不同的key的情况，是将这两个key区分开来的，是属于不同的观察项。所以应该用不同的SJKVOObserverItem实例来封装。#import #import typedef void(SJKVOBlock)(id observedObject, NSString *key, id oldValue, id newValue);interface SJKVOObserverItem : NSObjectproperty (nonatomic, strong) NSObject *observer;property (nonatomic, copy) NSString *key;property (nonatomic, assign) SEL setterSelector;property (nonatomic, assign) Method setterMethod;property (nonatomic, copy) SJKVOBlock block;- (instance