设计模式一日一练：中介者模式（Mediator）

Mediator模式，用一个中介对象来封装一系列的对象交互。中介者使各对象不需要显式的相互引用，从而使其耦合松散，而且可以独立地改变它们之间的交互。

比较典型的例子是联合国、QQ群等。比如，如果中国有事需要通知世界各国，可以通过联合国这一个机构，QQ群可以接收并发布每个成员的消息。

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/*
* file: Mediator.h
* brief: Created by night at 2016.12.07
*/

#ifndef __MEDIATOR_H__
#define __MEDIATOR_H__

#include <list>
#include <iostream>

using namespace std;

class Nation;
class Mediator {
public:
    virtual void Send(Nation* member, const char* msg) = 0;
};

class UnitedNationsMediator : public Mediator {
public:
    UnitedNationsMediator() { }

    void Register(Nation* member) { members.push_back(member); }

    void Send(Nation* member, const char* msg);

    list<Nation*> members;
};

class Nation {
public:
    Nation(const char* sname, Mediator* m) : name(sname), mediator(m) { }
    void Send(const char* msg) { mediator->Send(this, msg); }
    void Notify(const char* sender, const char* msg) { cout << name << "\t<-- " << sender << ":\t" << msg << endl; }

    const char* name;

protected:
    Mediator* mediator;
};

class China : public Nation
{
public:
    China(const char* sname, Mediator* m): Nation(sname, m) { }
};

class USA : public Nation
{
public:
    USA(const char* sname, Mediator* m) : Nation(sname, m) { }
};

class England : public Nation
{
public:
    England(const char* sname, Mediator* m) : Nation(sname, m) { }
};

void TestMediator();

#endif

---

/*
* file: Mediator.cpp
* brief: Created by night at 2016.12.07
*/

#include "Mediator.h"

void UnitedNationsMediator::Send(Nation* member, const char* msg) {
    for (list<Nation*>::iterator itr = members.begin(); itr != members.end(); itr++) {
        (*itr)->Notify(member->name, msg);
    }
}

void TestMediator()
{
    UnitedNationsMediator* mediator = new UnitedNationsMediator();
    China* china = new China("China", mediator);
    mediator->Register(china);

    USA* usa = new USA("USA", mediator);
    mediator->Register(usa);

    England* england = new England("England", mediator);
    mediator->Register(england);

    china->Send("This is from China!");
    cout << endl;

    usa->Send("This is from USA!");
    cout << endl;

    // destroy ...
    delete mediator;
    mediator = NULL;
    delete china;
    china = NULL;
    delete usa;
    usa = NULL;
    delete england;
    england = NULL;
}

---

输出结果：

China   <-- China:      This is from China!
USA     <-- China:      This is from China!
England <-- China:      This is from China!

China   <-- USA:        This is from USA!
USA     <-- USA:        This is from USA!
England <-- USA:        This is from USA!

---

引用

1. 《设计模式：可复用面向对象软件的基础》