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1.有时被称作发布/订阅模式,观察者模式定义了一种一对多的依赖关系,让多个观察者对象同时监听某一个主题对象。这个主题对象在状态发生变化时,会通知所有观察者对象,使它们能够自动更新自己。在oc中也常用到这种设计模式:KVO、通知。
2.模式中主要包括四部分:抽象主题、具体主题、抽象观察者、具体观察者
抽象主题(Subject):它把所有观察者对象的引用保存到一个聚集里,每个主题都可以有任何数量的观察者。抽象主题提供一个接口,可以增加和删除观察者对象。
具体主题(ConcreteSubject):将有关状态存入具体观察者对象;在具体主题内部状态改变时,给所有登记过的观察者发出通知。
抽象观察者(Observer):为所有的具体观察者定义一个接口,在得到主题通知时更新自己。
具体观察者(ConcreteObserver):实现抽象观察者角色所要求的更新接口,以便使本身的状态与主题状态协调
3.UML类图
百度百科上有个类图,觉得还可以,就截图贴了进来
4.实现
1.代码结构
2.代码实现
抽象主题 Subject.h
#import <Foundation/Foundation.h> #import "Observer.h" @protocol Subject <NSObject> -(void) attachObserver:(id<Observer>)observer; -(void) detachObserver:(id<Observer>)observer; -(void) notify; @end
具体主题 ConcreteSubject 实现抽象主题
#import <Foundation/Foundation.h> #include "Subject.h" #import "Observer.h" @interface ConcreteSubject : NSObject<Subject> @end
#import "ConcreteSubject.h" @interface ConcreteSubject () @property(nonatomic,strong) NSMutableArray *ObserverList; @end @implementation ConcreteSubject -(instancetype)init { self=[super init]; if (self) { _ObserverList=[[NSMutableArray alloc]init]; } return self; } -(void) attachObserver:(id<Observer>)observer { [self.ObserverList addObject:observer]; } -(void) detachObserver:(id<Observer>)observer { [self.ObserverList removeObject:observer]; } -(void) notify { NSLog(@"天气预报下大雨了"); for (id<Observer> observer in _ObserverList) { [observer update]; } } @end
抽象观察者
#import <Foundation/Foundation.h> @protocol Observer <NSObject> @optional //新闻联播 -(void)update; @end
具体观察者1
#import <Foundation/Foundation.h> #import "Observer.h" @interface ConcreteObserverOne : NSObject<Observer> @end
#import "ConcreteObserverOne.h" @implementation ConcreteObserverOne -(void)update { NSLog(@"下雨了可以卖伞了"); } @end
具体观察者2
#import <Foundation/Foundation.h> #import "Observer.h" @interface ConcreteObserverTwo : NSObject<Observer> @end
#import "ConcreteObserverTwo.h" @implementation ConcreteObserverTwo -(void)update { NSLog(@"下雨了不上班了"); } @end
运行:
#import <Foundation/Foundation.h> #import "ConcreteObserverOne.h" #import "ConcreteObserverTwo.h" #import "ConcreteSubject.h" int main(int argc, const char * argv[]) { @autoreleasepool { ConcreteSubject *subject=[[ConcreteSubject alloc]init]; ConcreteObserverOne *observer1=[[ConcreteObserverOne alloc]init]; [subject attachObserver:observer1]; ConcreteObserverTwo *observer2=[[ConcreteObserverTwo alloc]init]; [subject attachObserver:observer2]; [subject detachObserver:observer2]; [subject notify]; } return 0; }
#import <Foundation/Foundation.h> #import "ConcreteObserverOne.h" #import "ConcreteObserverTwo.h" #import "ConcreteSubject.h" int main(int argc, const char * argv[]) { @autoreleasepool { ConcreteSubject *subject=[[ConcreteSubject alloc]init]; ConcreteObserverOne *observer1=[[ConcreteObserverOne alloc]init]; [subject attachObserver:observer1]; ConcreteObserverTwo *observer2=[[ConcreteObserverTwo alloc]init]; [subject attachObserver:observer2]; [subject detachObserver:observer2]; [subject notify]; } return 0; }
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原文地址:http://www.cnblogs.com/5ishare/p/4766939.html