Objective-C設計模式——中介者Mediator（物件去耦）

中介者模式

中介者模式很好的詮釋了迪米特法則，任意兩個不相關的物件之間如果需要關聯，那麼需要通過第三個類來進行。中介者就是把一組物件進行封裝，遮蔽了類之間的互動細節，使不同的類直接不需要持有對方引用也可以進行訪問。

中介者Mediator會持有同事類（就是需要處理互動邏輯的物件）Colleague的引用，同時每個colleague也會持有Mediator一份引用。這樣colleague如果有任何和別的類互動的請求就會發給Mediator，對改組物件進行了解耦合。其實我們平時經常寫的檢視控制器本身就是一箇中介中，它來控制著不同物件之間的互動行為。

 

應用場景

物件間互動雖然定義明確然而非常複雜，導致一組物件彼此相互依賴而且難以理解；

因為物件引用了許多其他物件並與其通訊，導致物件難以複用；

想要定製一個分佈在多個類中的邏輯或行為，又不想生成太多子類。

 

中介者的優缺點

優點

Mediator出現減少了各個Colleague的耦合，使得可以獨立地改變和複用各個Colleague類和Mediator，由於把物件如何寫作進行了抽象，將中介者作為一個獨立的概念並將其封裝在一個物件中，這樣關注的物件就從物件各自本身的行為轉移到它們之間的互動上，也就是站在一個更巨集觀的角度去看待系統。

缺點

由於ConcreteMediator控制了集中化，於是就把互動複雜性變為了中介者的複雜性，這就使得中介者會變得比任何一個ConcreteColleague都複雜。

 

Demo

Colleague

#import <Foundation/Foundation.h>

@class Mediator;
@interface Colleague : NSObject

@property (nonatomic, weak) Mediator* mediator;

-(instancetype)initWithMediator:(Mediator *)mediator;

-(void)notifyAnother;
-(void)notified:(NSString *)message;


@end


#import "Colleague.h"
#import "Mediator.h"

@implementation Colleague

-(instancetype)initWithMediator:(Mediator *)mediator
{
    self = [super init];
    if(self)
    {
        _mediator = mediator;
    }
    return self;
}

-(void)notified:(NSString *)message
{
    NSLog(@"%@",message);
}

-(void)notifyAnother
{
    [self.mediator notify:self];
}

@end


#import "Colleague.h"

@interface ConcreteColleagueA : Colleague

@end

#import "ConcreteColleagueA.h"

@implementation ConcreteColleagueA

@end

#import "Colleague.h"

@interface ConcreteColleagueB : Colleague

@end

#import "ConcreteColleagueB.h"

@implementation ConcreteColleagueB

@end

在OC中為了避免引用迴圈，所以Colleague的Mediator物件修飾符用weak

 

Mediator

#import <Foundation/Foundation.h>
#import "ConcreteColleagueA.h"
#import "ConcreteColleagueB.h"

@interface Mediator : NSObject

@property (nonatomic ,strong) ConcreteColleagueA *colleagueA;
@property (nonatomic ,strong) ConcreteColleagueB *colleagueB;

-(void)notify:(NSObject *)obj;

@end

#import "Mediator.h"

@implementation Mediator

-(id)init
{
    self = [super init];
    if(self)
    {
        
    }
    return self;
}

-(void)notify:(NSObject *)obj
{
    if (obj == self.colleagueA)
    {
        [self.colleagueB notified:@"B notified"];
    }
    else
    {
        [self.colleagueA notified:@"A notified"];
    }
}

@end

客戶端

        Mediator *mediator = [[Mediator alloc] init];
          
        ConcreteColleagueA *colleagueA = [[ConcreteColleagueA alloc] initWithMediator:mediator];
        ConcreteColleagueB *colleagueB = [[ConcreteColleagueB alloc] initWithMediator:mediator];
        
        mediator.colleagueA = colleagueA;
        mediator.colleagueB = colleagueB;
        
        [colleagueA notifyAnother];
        [colleagueB notifyAnother];

2015-07-26 16:48:42.508 Mediator[3888:1799182] B notified
2015-07-26 16:48:42.509 Mediator[3888:1799182] A notified