書讀百變，其義自見！

將KVO形式以程式碼實現呈現，通俗易懂，更容易掌握 ：GitHub

一、KVO-基本使用方法

//註冊
- (void)addObserver:(NSObject *)observer forKeyPath:(NSString *)keyPath options:(NSKeyValueObservingOptions)options context:(nullable void *)context;

//監聽方法
- (void)observeValueForKeyPath:(nullable NSString *)keyPath ofObject:(nullable id
 
)object change:(nullable NSDictionary<NSKeyValueChangeKey, id> *)change context:(nullable void *)context;

//移除
- (void)removeObserver:(NSObject *)observer forKeyPath:(NSString *)keyPath context:(nullable void *)context API_AVAILABLE(macos(10.7), ios(5.0), watchos(2.0), tvos(9.0));
- (void)removeObserver:(NSObject *)observer forKeyPath:(NSString *)keyPath;

 
//監聽模式（手動，自動）,預設是自動Yes
+(BOOL)automaticallyNotifiesObserversForKey:(NSString *)key;


//屬性的依賴，返回監聽屬性類的集合

+(NSSet<NSString *> *)keyPathsForValuesAffectingValueForKey:(NSString *)key；