行为型之七-观察者模式

Observer（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。

iOS中的KVO、NSNotication都是观察者模式。

VC.m

HCDSubject *subject = [[HCDSecreteSubject alloc]init];
//添加三个通知对象
HCDObserver nbaobserver = [[HCDNBAObserver alloc]init];
[subject attach:nbaobserver];
HCDObserver stockobserver = [[HCDStockObserver alloc]init];
[subject attach:stockobserver];
HCDObserver stockobserver1 = [[HCDStockObserver alloc]init];
[subject attach:stockobserver1];
//删除一个通知对象
[subject detach:stockobserver];

[subject notify];

HCDObserver.h

@protocol HCDObserver <NSObject>
@optional
-(void)update;
@end

HCDSubject.h

@interface HCDSubject : NSObject
-(void)attach:(id<HCDObserver>)observer;
-(void)detach:(id<HCDObserver>)observer;
-(void)notify;
-(NSArray *)getobserverList;
@end

HCDSubject.m

@interface HCDSubject ()
@property(nonatomic,readwrite,strong)NSMutableArray *observerList;
@end
@implementation HCDSubject
-(instancetype)init{
    self = [super init];
    if (self) {
        _observerList = [NSMutableArray array];
    }
    return self;
}
-(void)attach:(id<HCDObserver>)observer{
    [self.observerList addObject:observer];
}
-(void)detach:(id<HCDObserver>)observer{
    for (id<HCDObserver> currentObserver in [self getobserverList]) {
        if (currentObserver == observer) {
            [self.observerList removeObject:observer];
        }
    }
}
-(NSMutableArray *)getobserverList{
    return [NSMutableArray arrayWithArray:self.observerList];
}
-(void)notify{
    
}
@end

HCDSecreteSubject.h

@interface HCDSecreteSubject : HCDSubject

@end

HCDSecreteSubject.m

@implementation HCDSecreteSubject
-(void)notify{
    NSLog(@"秘书通知：老板回来了，大家赶紧撤");
    for (id<HCDObserver> observer in [self getobserverList]) {
        [observer update];
    }
}
@end

设计图