//注册
- (void)addObserver:(NSObject *)observer forKeyPath:(NSString *)keyPath options:(NSKeyValueObservingOptions)options context:(nullable void *)context;//监听方法
- (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;//监听模式（手动，自动）,默认是自动Yes
+(BOOL)automaticallyNotifiesObserversForKey:(NSString *)key;//属性的依赖，返回监听属性类的集合+(NSSet<NSString *> *)keyPathsForValuesAffectingValueForKey:(NSString *)key；

//
//  ViewController.m
//  KVO-基本用法
//
//  Created by GuoYanjun on 2019/1/9.
//  Copyright © 2019年 shiyujin. All rights reserved.
//

#import "ViewController.h"
#import "Person.h"
@interface ViewController ()
@property(nonatomic,strong)Person *p;
@end@implementation ViewController- (void)viewDidLoad {[super viewDidLoad];_p=[[Person alloc]init];
//    注册
    [_p addObserver:self forKeyPath:NSStringFromSelector(@selector(name)) options:NSKeyValueObservingOptionNew context:nil];}//监听方法
-(void)observeValueForKeyPath:(NSString *)keyPath ofObject:(id)object change:(NSDictionary<NSKeyValueChangeKey,id> *)change context:(void *)context{NSLog(@"%@",change);
}
-(void)touchesBegan:(NSSet<UITouch *> *)touches withEvent:(UIEvent *)event{//    自动模式static int a =0;_p.name = [NSString stringWithFormat:@"%d",a++];//    手动
//    [_p willChangeValueForKey:@"name"];
//    _p.name = [NSString stringWithFormat:@"%d",a++];
//    [_p didChangeValueForKey:@"name"];
//

}
-(void)dealloc{[_p removeObserver:self forKeyPath:@"name"];
}
@end

    self->_p->isa:Person改变为self->_p->isa:NSKVONotifying_Person

//    [_p.arry addObject:[NSString stringWithFormat:@"%d",a++]];//这一步不会触发监听方法因为监听是监听set的方法，addObject不是set方法//解决方法NSMutableArray *tenp =[_p mutableArrayValueForKey:@"arry"];[tenp addObject:[NSString stringWithFormat:@"%d",a++]];

#import <Foundation/Foundation.h>NS_ASSUME_NONNULL_BEGIN@interface NSObject (JK_KVO)
- (void)JK_addObserver:(NSObject *)observer forKeyPath:(NSString *)keyPath options:(NSKeyValueObservingOptions)options context:(nullable void *)context;
@endNS_ASSUME_NONNULL_END

#import "NSObject+JK_KVO.h"
#import <objc/message.h>@implementation NSObject (JK_KVO)- (void)JK_addObserver:(NSObject *)observer forKeyPath:(NSString *)keyPath options:(NSKeyValueObservingOptions)options context:(nullable void *)context{//   1.创建一个类 -- self.class 就是PersonNSString *oldname = NSStringFromClass(self.class);NSString *newNem = [@"JKKVO_" stringByAppendingString:oldname];Class myclass = objc_allocateClassPair(self.class, newNem.UTF8String, 0);// 注册类
    objc_registerClassPair(myclass);//    2.重写子类set方法 -- 所谓的重写就是给子类添加f这个方法 setName,因为子类没有父类的setName方法！！！/* class ：给那个类添加方法*sel:方法编号*imp ：方法实现（函数指针）*type :返回值类型*/class_addMethod(myclass, @selector(setName:), (IMP)setName, "v@:@");//    3.修改isa指针
    object_setClass(self, myclass);//    4.将观察保存到当前对象objc_setAssociatedObject(self, @"observer", observer, OBJC_ASSOCIATION_ASSIGN);}void setName(id self,SEL _cmd,NSString *newName){NSLog(@"来了--%@",newName);
//    调用父类的setName方法Class class =[self class];object_setClass(self, class_getSuperclass(class));//改成父类
    objc_msgSend(self,@selector(setName:),newName);//发送消息给父类//    观察者id observer = objc_getAssociatedObject(self, @"observer");if (observer) {objc_msgSend(observer, @selector(observeValueForKeyPath:ofObject:change:context:),@"name",self,@{@"new:":newName,@"kind:":@"1"},nil);}//    改回子类object_setClass(self, class);
}
@end

 [_p JK_addObserver:self forKeyPath:@"name" options:NSKeyValueObservingOptionNew context:nil];