KVO

person.h

#import <Foundation/Foundation.h>

#import "Watcher.h"

@class Watcher;

@interface Person : NSObject

@property (nonatomic,strong)NSString *name;

@property (nonatomic,strong)NSString *address;

@property (nonatomic,strong)Watcher *watcher;

-(void)addWatcher:(Watcher *)watcher;

-(void)update;

@end

person.m

#import "Person.h"

@implementation Person

-(void)addWatcher:(Watcher *)watcher

{

    self.watcher = watcher;

    //为当前类添加一个观察者，当地址发生变化时，观察者会接收到通知

    [selfaddObserver:_watcherforKeyPath:@"address"options:NSKeyValueObservingOptionNew |

        NSKeyValueObservingOptionOld

        context:@"address changed"];

}

-(void)update

{

    self.address =@"beijing";

}

-(void)dealloc

{

    //移除观察者

    [selfremoveObserver:_watcherforKeyPath:@"address"];

}

@end

watcher.h

#import <Foundation/Foundation.h>

@interface Watcher : NSObject

@end

watcher.m

#import "Watcher.h"

@implementation Watcher

//观察者必须要实现这个方法，用于接收被观察者发来的通知，并进行处理

-(void)observeValueForKeyPath:(NSString *)keyPath ofObject:(id)object change:(NSDictionary<NSString *,id> *)change context:(void *)context

{

    NSLog(@"obj:%@ change:%@ keyPath:%@,context:%@",object,change,keyPath,context);

    NSString *newAddress = [objectvalueForKeyPath:keyPath];

    NSLog(@"%@:%@",context,newAddress);

}

@end

main.m

#import <Foundation/Foundation.h>

#import "Person.h"

#import "Watcher.h"

int main(int argc,const char * argv[]) {

    @autoreleasepool {

        Person *person = [[Personalloc]init];

        Watcher *watcher = [[Watcheralloc]init];

        [person addWatcher:watcher];

        person.address =@"beijing";

        person.address =@"shanghai";

        

    }

    return0;

}