• TCJPerson类中的方法没有改变（imp实现地址没有变化）
• NSKVONotifying_TCJPerson类中重写了父类TCJPerson的dealloc方法
• NSKVONotifying_TCJPerson类中重写了基类NSObject的class方法和_isKVOA方法
  • 重写的class方法可以指回TCJPerson类
• NSKVONotifying_TCJPerson类中重写了父类TCJPerson的setNickName方法
  • 因为子类只继承、不重写是不会有方法imp的，调用方法时会问父类要方法实现
  • 且两个setNickName的地址指针不一样
  • 每观察一个属性变量就重写一个setter方法（可自行论证）

根据KVO的官方文档和上述结论，我们将自定义KVO——下面的自定义会有runtime-API的使用和接口设计思路的讲解，最终的自定义KVO能满足基本使用的需求但仍不完善。系统的KVO回调和自动移除观察者都与注册逻辑分层，自定义的KVO将使用block回调和自动释放来优化这一点不足

-(void)cj_addObserver:(NSObject *)observer forKeyPath:(NSString *)keyPath block:(TCJKVOBlock)block;

if (keyPath == nil || keyPath.length == 0) return; // if (![self isContainProperty:keyPath]) return; if (![self isContainSetterMethodFromKeyPath:keyPath]) return; // 判断属性是否存在 - (BOOL)isContainProperty:(NSString *)keyPath { unsigned int number; objc_property_t *propertiList = class_copyPropertyList([self class], &number); for (unsigned int i = 0; i < number; i++) { const char *propertyName = property_getName(propertiList[i]); NSString *propertyString = [NSString stringWithUTF8String:propertyName]; if ([keyPath isEqualToString:propertyString]) return YES; } free(propertiList); return NO; }/// 判断setter方法 - (BOOL)isContainSetterMethodFromKeyPath:(NSString *)keyPath { Class superClass= object_getClass(self); SEL setterSeletor= NSSelectorFromString(setterForGetter(keyPath)); Method setterMethod = class_getInstanceMethod(superClass, setterSeletor); if (!setterMethod) { NSLog(@"没找到该属性的setter方法%@", keyPath); return NO; } return YES; }

BOOL isAutomatically = [self fx_performSelectorWithMethodName:@"automaticallyNotifiesObserversForKey:" keyPath:keyPath]; if (!isAutomatically) return; // 动态调用类方法 - (BOOL)fx_performSelectorWithMethodName:(NSString *)methodName keyPath:(id)keyPath {if ([[self class] respondsToSelector:NSSelectorFromString(methodName)]) {#pragma clang diagnostic push #pragma clang diagnostic ignored "-Warc-performSelector-leaks" BOOL i = [[self class] performSelector:NSSelectorFromString(methodName) withObject:keyPath]; return i; #pragma clang diagnostic pop } return NO; }

// 动态生成子类 Class newClass = [self createChildClassWithKeyPath:keyPath]; - (Class)createChildClassWithKeyPath:(NSString *)keyPath { NSString *oldClassName = NSStringFromClass([self class]); NSString *newClassName = [NSString stringWithFormat:@"%@%@", kTCJKVOPrefix, oldClassName]; Class newClass = NSClassFromString(newClassName); // 防止重复创建生成新类 if (newClass) return newClass; // 申请类 newClass = objc_allocateClassPair([self class], newClassName.UTF8String, 0); // 注册类 objc_registerClassPair(newClass); // class的指向是TCJPerson SEL classSEL = NSSelectorFromString(@"class"); Method classMethod = class_getInstanceMethod([self class], classSEL); const char *classTypes = method_getTypeEncoding(classMethod); class_addMethod(newClass, classSEL, (IMP)cj_class, classTypes); return newClass; }

object_setClass(self, newClass);

typedef void(^TCJKVOBlock)(id observer,NSString *keyPath,id oldValue,id newValue); @interface TCJKVOInfo : NSObject @property (nonatomic, weak) NSObject *observer; @property (nonatomic, copy) NSString *keyPath; @property (nonatomic, copy) TCJKVOBlock handleBlock; @end@implementation TCJKVOInfo- (instancetype)initWitObserver:(NSObject *)observer forKeyPath:(NSString *)keyPath handleBlock:(TCJKVOBlock)block { if (self=[super init]) { _observer = observer; _keyPath= keyPath; _handleBlock = block; } return self; } @end// 保存信息 TCJKVOInfo *info = [[TCJKVOInfo alloc] initWitObserver:observer forKeyPath:keyPath handleBlock:block]; NSMutableArray *mArray = objc_getAssociatedObject(self, (__bridge const void * _Nonnull)(kTCJKVOAssiociateKey)); if (!mArray) { mArray = [NSMutableArray arrayWithCapacity:1]; objc_setAssociatedObject(self, (__bridge const void * _Nonnull)(kTCJKVOAssiociateKey), mArray, OBJC_ASSOCIATION_RETAIN_NONATOMIC); } [mArray addObject:info];

- (Class)createChildClassWithKeyPath:(NSString *)keyPath { ... // 添加setter SEL setterSEL = NSSelectorFromString(setterForGetter(keyPath)); Method setterMethod = class_getInstanceMethod([self class], setterSEL); const char *setterTypes = method_getTypeEncoding(setterMethod); class_addMethod(newClass, setterSEL, (IMP)cj_setter, setterTypes); return newClass; }

static void cj_setter(id self,SEL _cmd,id newValue) { NSString *keyPath = getterForSetter(NSStringFromSelector(_cmd)); id oldValue = https://www.it610.com/article/[self valueForKey:keyPath]; // 改变父类的值 --- 可以强制类型转换 void (*cj_msgSendSuper)(void *,SEL , id) = (void *)objc_msgSendSuper; struct objc_super superStruct = { .receiver = self, .super_class = class_getSuperclass(object_getClass(self)), }; cj_msgSendSuper(&superStruct,_cmd,newValue); // 信息数据回调 NSMutableArray *mArray = objc_getAssociatedObject(self, (__bridge const void * _Nonnull)(kTCJKVOAssiociateKey)); for (FXKVOInfo *info in mArray) { if ([info.keyPath isEqualToString:keyPath] && info.handleBlock) { info.handleBlock(info.observer, keyPath, oldValue, newValue); } } }

- (Class)createChildClassWithKeyPath:(NSString *)keyPath { ... // 添加dealloc SEL deallocSEL = NSSelectorFromString(@"dealloc"); Method deallocMethod = class_getInstanceMethod([self class], deallocSEL); const char *deallocTypes = method_getTypeEncoding(deallocMethod); class_addMethod(newClass, deallocSEL, (IMP)cj_dealloc, deallocTypes); return newClass; }

static void cj_dealloc(id self, SEL _cmd) { Class superClass = [self class]; object_setClass(self, superClass); }

• 取出基类NSObject的dealloc实现与cj_dealloc进行方法交换
• isa指回去之后继续调用真正的dealloc进行释放
• 之所以不在+load方法中进行交换，一是因为效率低，二是因为会影响到所有类

- (Class)createChildClassWithKeyPath:(NSString *)keyPath { ... // 添加dealloc //SEL deallocSEL = NSSelectorFromString(@"dealloc"); //Method deallocMethod = class_getInstanceMethod([self class], deallocSEL); //const char *deallocTypes = method_getTypeEncoding(deallocMethod); //class_addMethod(newClass, deallocSEL, (IMP)cj_dealloc, deallocTypes); static dispatch_once_t onceToken; dispatch_once(&onceToken, ^{ [self cj_methodSwizzlingWithClass:[self class] oriSEL:NSSelectorFromString(@"dealloc") swizzledSEL:@selector(cj_dealloc)]; }); return newClass; }- (void)cj_dealloc { Class superClass = [self class]; object_setClass(self, superClass); [self cj_dealloc]; }

就这样自定义KVO将KVO三部曲用block形式合成一步

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