1. 意图
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地相互引用，从而使其耦合松散，
而且可以独立地改变它们之间的交互。
2. 四种角色
抽象中介者(Mediator)、具体中介者(Concrete Mediator)、抽象同事(Colleague)、
具体同事(Concrete Colleague)
3. 优点
3.1 减少了子类生成。
3.2 将各个Colleague解耦。
3.3 简化了对象协议。
3.4 对对象如何协作进行了抽象。
4. 缺点
4.1 使控制集中化，可能使中介者自身称为一个难于维护的庞然大物
5. 相关模式
5.1 Mediator的协议是多向的，提供了Colleague对象间的协作行为；
而Façade的协议是单向的，只能Façade对子系统提出请求。
5.2 Colleague可使用Observer模式与Mediator通信。
6. 代码示意(C++)
#pragma once
#include <iostream>
#include <string>
#include <vector>
using namespace std;
class Colleague;
class Mediator
{
public:
virtual void SendMessage(const string& message, Colleague* pFrom) = 0;
virtual void AddColleague(Colleague* pColleague) = 0;
};
class ConcreteMediator :public Mediator
{
vector<Colleague*> m_colleagues;
public:
virtual void SendMessage(const string& message, Colleague* pFrom);
virtual void AddColleague(Colleague* pColleague);
};
class Colleague
{
string m_strName;
Mediator* m_pMediator;
public:
Colleague(Mediator* pMediator, const string& strName) {
m_pMediator = pMediator;
m_strName = strName;
}
void SendMessage(const string& message) {
m_pMediator->SendMessage(message, this);
}
string GetName() { return m_strName; }
virtual void GetMessage(const string& message, const string& name) = 0;
};
class ConcreteColleage1 :public Colleague
{
public:
ConcreteColleage1(Mediator* pMediator) :Colleague(pMediator, "ConcreteColleage1") {
}
virtual void GetMessage(const string& message, const string& name) {
cout << "ConcreteColleage1 got message:" << message << ",from:" << name << endl;
}
};
class ConcreteColleage2 :public Colleague
{
public:
ConcreteColleage2(Mediator* pMediator) :Colleague(pMediator, "ConcreteColleage2") {
}
virtual void GetMessage(const string& message, const string& name) {
cout << "ConcreteColleage2 got message:" << message << ",from:" << name << endl;
}
};Mediator.cpp:
#include "Mediator.h"
void ConcreteMediator::SendMessage(const string& message, Colleague* pFrom) {
auto it = m_colleagues.begin();
while (it != m_colleagues.end()) {
if (pFrom != (*it)) {
(*it)->GetMessage(message, pFrom->GetName());
}
++it;
}
}
void ConcreteMediator::AddColleague(Colleague* pColleague) {
m_colleagues.emplace_back(pColleague);
}#include "Mediator.h"
int main() {
Mediator* pMediator = new ConcreteMediator();
Colleague* pColleague1 = new ConcreteColleage1(pMediator);
Colleague* pColleague2 = new ConcreteColleage2(pMediator);
pMediator->AddColleague(pColleague1);
pMediator->AddColleague(pColleague2);
pColleague1->SendMessage("hello");
pColleague2->SendMessage("hi");
delete pColleague1;
delete pColleague2;
delete pMediator;
return 0;
}运行结果：
6.1 ConcreteColleage之间不直接打交道，消息通过ConcreteMediator传递(3.2)。
6.2 将多对多的关系变成了一对多(一个中介对多个同事)的关系(3.3)。
