iOS设计模式 (六) 观察者模式

观察者模式

• 观察者模式本质上时一种发布-订阅模型,用以消除具有不同行为的对象之间的耦合，通过这一模式，不同对象可以协同工作，同时它们也可以被复用于其他地方Observer从Subject订阅通知，ConcreteObserver实现重现ObServer并将其重载其update方法。一旦SubJect的实例需要通知Observer任何新的变更，Subject会发送update消息来通知存储在其内部类中所注册的Observer、在ConcreteObserver的update方法的实际实现中，Subject的内部状态可被取得并进行后续处理。其类图如下

观察者UML

• 可以发现观察者模式无非在是定义对象间的一种一对多的依赖关系，并且当一个对象的状态发生改变的时候，所有依赖于它的对象都会得到通知且自动更新。即如果Subject允许其他观察者(实现了观察者接口的对象)对这个Subject的改变进行请阅，当Subject发送了变化，那么Subject会将这个变化发送给所有的观察者，观察者就能对Subject的变化做出更新.

观察者demo实例

• ObserverCenterProtocol 协议类

#import <Foundation/Foundation.h>
@protocol ObserverCenterProtocol <NSObject>

//用户的信息和从某一刊物接受的信息
- (void)accpetUserMessage:(id)userMessage subNumber:(NSString *)subNumber;

@end

• ObserverCenter 类

#import <Foundation/Foundation.h>
#import "ObserverCenterProtocol.h"

@interface ObserverCenter : NSObject

// 创建书刊订阅号
+ (void)createNumber:(NSString *)observerNumber;

//移除订阅号
+ (void)removeNumebr:(NSString *)observerNumer;

//添加用户
+ (void)addUser:(id<ObserverCenterProtocol>)user withNumebr:(NSString *)observerNumber;

//移除用户
+ (void)removeUser:(id<ObserverCenterProtocol>)user withNumebr:(NSString *)observerNumber;

//发送消息
+ (void)sendMessage:(id)message withNumber:(NSString *)number;

@end

#import "ObserverCenter.h"

static NSMutableDictionary *_observerDict = nil;

@implementation ObserverCenter

+ (void)initialize
{
    if (self == [ObserverCenter class]) {
        _observerDict = [NSMutableDictionary dictionary];
    }
}

//创建书刊订阅号
+ (void)createNumber:(NSString *)observerNumber
{
    NSHashTable *hashTable = [self existNumber:observerNumber];
    if (hashTable == nil) {
        hashTable = [NSHashTable weakObjectsHashTable];
        [_observerDict setObject:hashTable forKey:observerNumber];
    }
}

//移除订阅号
+ (void)removeNumebr:(NSString *)observerNumer
{
    NSHashTable *hashTable = [self existNumber:observerNumer];
    if (hashTable) {
        [_observerDict removeObjectForKey:observerNumer];
    }
}

//添加用户
+ (void)addUser:(id<ObserverCenterProtocol>)user withNumebr:(NSString *)observerNumber
{
    NSHashTable *hashTable = [self existNumber:observerNumber];
    [hashTable addObject:user];
    
}

//移除用户
+ (void)removeUser:(id<ObserverCenterProtocol>)user withNumebr:(NSString *)observerNumber
{
    NSHashTable *hashTable = [self existNumber:observerNumber];
    [hashTable removeObject:user];
}

//发送消息
+ (void)sendMessage:(id)message withNumber:(NSString *)number
{
    //获取订阅号
    NSHashTable *hashTable = [self existNumber:number];
    
    if (hashTable) {
        NSEnumerator *enumerator  = [hashTable objectEnumerator];
        
        id <ObserverCenterProtocol> object = nil;
        
        while (object = [enumerator nextObject]) {
            
            NSLog(@"xxxxxx:%@",[enumerator nextObject]);
            if ([object respondsToSelector:@selector(accpetUserMessage:subNumber:)]) {
                
                [object accpetUserMessage:message subNumber:number];
            }
        }
    }
}


+ (NSHashTable *)existNumber:(NSString *)number
{
      return [_observerDict objectForKey:number];
}

@end

• ViewController 类

#import "ViewController.h"
#import "ObserverCenter.h"

static NSString *OBSERVER = @"OBSERVER";

@interface ViewController ()<ObserverCenterProtocol>

@end

@implementation ViewController

- (void)viewDidLoad {
    [super viewDidLoad];
    
    // 创建订阅号
    [ObserverCenter createNumber:OBSERVER];
    
    // 添加订阅的用户到指定的书刊上
    [ObserverCenter addUser:self withNumebr:OBSERVER];
    
    // 发送消息
    [ObserverCenter sendMessage:@"2.22" withNumber:OBSERVER ];
}

- (void)accpetUserMessage:(id)userMessage subNumber:(NSString *)subNumber
{
    
    NSLog(@"uuserMessagese ====== :%@ subNumber ======:%@",userMessage,subNumber);
}

@end

• demo 地址：https://github.com/defuliu/ObserverPattern.git
• NSHashTable 详解见：https://www.jianshu.com/p/de71385930ba