Person.h

#import<Foundation/Foundation.h>

@classAccount;

@interfacePerson :NSObject{

@private

   int_age;

}

#pragma mark -属性

@property(nonatomic,copy)NSString*name;

@property(nonatomic,retain)Account*account;

-(void)showMessage;

@end

Person.m

#import"Person.h"

#import"Account.h"

@implementationPerson

-(void)showMessage{

   NSLog(@"name=%@,age=%d",_name,_age);

}

#pragma mark设置人员账户

-(void)setAccount:(Account*)account{

   _account=account;

   //添加对Account的监听

    [_accountaddObserver:selfforKeyPath:@"balance"options:NSKeyValueObservingOptionNewcontext:nil];

}

#pragma mark重写observeValueForKeyPath方法，当账户余额变化后此处获得通知

-(void)observeValueForKeyPath:(NSString*)keyPath ofObject:(id)object change:(NSDictionary*)change context:(void*)context{

   if([keyPathisEqualToString:@"balance"]){//这里只处理balance属性

       NSLog(@"keyPath=%@,object=%@,newValue=%.2f,context=%@",keyPath,object,[[changeobjectForKey:@"new"]floatValue],context);

    }

}

#pragma mark重写销毁方法

-(void)dealloc{

    [self.accountremoveObserver:selfforKeyPath:@"balance"];//移除监听

}

Account.h

#import<Foundation/Foundation.h>

@interfaceAccount :NSObject

#pragma mark余额

@property(nonatomic,assign)floatbalance;

@end

Account.m

#import"Account.h"

@implementationAccount

@end

Main调用方法

- (void)viewDidLoad {

    [superviewDidLoad];

#if0

    Person *person1=[[Person alloc]init];

    [person1 setValue:@"Kenshin"forKey:@"name"];

    [person1 setValue:@28forKey:@"age"];//注意即使一个私有变量仍然可以访问

    [person1 showMessage];

   //结果：name=Kenshin,age=28

    NSLog(@"person1's name is :%@,age is :%@",person1.name,[person1 valueForKey:@"age"]);

   //结果：person1's name is :Kenshin,age is :28

    Account *account1=[[Account alloc]init];

    person1.account=account1;//注意这一步一定要先给account属性赋值，否则下面按路径赋值无法成功，因为account为nil，当然这一步骤也可以写成:[person1 setValue:account1 forKeyPath:@"account"];

    [person1 setValue:@.0forKeyPath:@"account.balance"];

    NSLog(@"person1's balance is :%.2f",[[person1 valueForKeyPath:@"account.balance"] floatValue]);

   //结果：person1's balance is :100000000.00

#else

   Person*person1=[[Personalloc]init];

    person1.name=@"Kenshin";

   Account*account1=[[Accountalloc]init];

    account1.balance=100000000.0;

    person1.account=account1;

    account1.balance=200000000.0;//注意执行到这一步会触发监听器回调函数observeValueForKeyPath: ofObject: change: context:

#endif

}