中介者模式

用一箇中介物件來封裝一系列的物件互動。中介者使個各物件不需要顯式地相互引用，從而使其耦合鬆散，而且可以獨立地改變它們之間的互動。

本文講解中介者模式框架，程式碼使用C++語言描述，程式碼存在的不足或問題有望各位指出。

中介者模式程式碼框架

//中介者模式
#include <iostream>
#include <string>
using namespace std;
class Colleague;
class ConcreteColleague1;
class ConcreteColleague2;
class Mediator
{
public
 
:
    virtual ~Mediator(){}
    virtual void send(string message, Colleague *colleague) =0;
protected:
    Mediator(){}
};

class Colleague
{
public:
    virtual ~Colleague(){}

protected:
    Colleague(){}
    Colleague(Mediator *mediator)
    {
        this->mediator = mediator;

    }
protected
 
:
    Mediator *mediator =nullptr;
};


class ConcreteMediator : public Mediator
{
public:
    ConcreteMediator(){}
    ~ConcreteMediator(){}
    void setColleague1(ConcreteColleague1 *colleague1)
    {
        this->colleague1 = colleague1;
    }
    void setColleague2(ConcreteColleague2 *colleague2)
    {
        this
 
->colleague2 = colleague2;
    }
    void send(string message, Colleague *colleague) override;


private:
    ConcreteColleague1 *colleague1;
    ConcreteColleague2 *colleague2;
};




class ConcreteColleague1: public Colleague
{
public:
    ConcreteColleague1(Mediator *mediator)
    {
        this->mediator = mediator;
    }
    void send(string message)
    {
        mediator->send(message,this);
    }

    void notify(string message)
    {
        cout << "同事1得到訊息：" << message <<endl;
    }

};



class ConcreteColleague2: public Colleague
{
public:
    ConcreteColleague2(Mediator *mediator)
    {
        this->mediator = mediator;
    }
    void send(string message)
    {
        mediator->send(message,this);
    }

    void notify(string message)
    {
        cout << "同事2得到訊息：" << message <<endl;
    }

};


void ConcreteMediator::send(string message, Colleague *colleague)
{
    if(colleague == colleague1 )
    {
        colleague2->notify(message);
    }
    else
    {
        colleague1->notify(message);
    }
}

int main()
{
    ConcreteMediator *m = new ConcreteMediator();
    ConcreteColleague1 *c1 = new ConcreteColleague1(m);
    ConcreteColleague2 *c2 = new ConcreteColleague2(m);
    m->setColleague1(c1);
    m->setColleague2(c2);
    c1->send("吃過飯了嗎？");
    c2->send("沒有呢，你打算請客嗎？");
    delete m;
    delete c1;
    delete c2;
    return 0;

}

中介者模式優缺點

1、中介者模式很容易在系統中應用，也很容易在系統中誤用。當系統出現了‘多對多’互動複雜的物件群時，不要急於使用中介者模式，而要先反思你的系統在設計上是不是合理。

2、Mediator的出現減少了各個Colleague的耦合，使得可以獨立地改變和複用各個Colleague類和Mediator；其次，由於把物件如何協作進行了抽象，將中介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來，也就是站在一個更巨集觀的角度去看待系統。

3、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。