介绍 [1]
观察者模式最重要的一个核心思想就是一个类是消息源，这个类负责给若干个需要这个消息的类进行传消息。只要能实现这个目的即可。在C++中其实有很简单的实现方法，那就是在消息源这个类中申明一个list，里边存放需要接受消息的类。然后负责操作这个list即可。
例子介绍
这个例子的背景是球员和教练。这里把教练的命令可以理解为消息源。然后把那么场上的球员理解为观察者。然后，消息源（教练）发出指令，观察者（球员）收到指令后做出相应的动作。
UML类图
#include <iostream>
#include <list>
#include <string.h>
using namespace std;
class Command;
//这个类作为观察者的抽象基类
class Player
{
public:
Player(string name,Command *command)
{
this->name = name;
this->m_command = command;
}
virtual void execCommand(string content) = 0;
string Name()
{
return name;
}
protected:
string name;
Command *m_command;
};
class Forward:public Player
{
public:
Forward(string name,Command *command):Player(name,command)
{
}
void execCommand(string content);
};
class Guard:public Player
{
public:
Guard(string name,Command *command):Player(name,command)
{
}
void execCommand(string content);
};
class Command
{
public:
virtual void attach(Player *player) = 0;
virtual void detach(Player *player) = 0;
virtual void notify(string content) = 0;
protected:
list<Player *> m_list;
};
class CoachCommand:public Command
{
public:
void attach(Player *player)
{
m_list.push_back(player);
}
void detach(Player *player)
{
list<Player *>::iterator item = m_list.begin();
while(item != m_list.end())
{
if((*item) == player)
{
cout<<player->Name()<<"被换下场"<<endl;
item = m_list.erase(item);
}
else
++item;
}
}
void notify(string content)
{
list<Player *>::iterator it;
for(it = m_list.begin() ; it != m_list.end() ; it ++)
{
(*it)->execCommand(content);
}
}
};
void Forward::execCommand(string content)
{
if(content == "开始强攻")
cout<<name<<"收到："<<content<<"的指令，然后采取："<<"开启疯抢模式的战术"<<endl;
if(content == "开始防守")
cout<<name<<"收到："<<content<<"的指令，然后采取："<<"回到本方半场进行防守，伺机进行反击的战术"<<endl;
}
void Guard::execCommand(string content)
{
if(content == "开始强攻")
cout<<name<<"收到："<<content<<"的指令，然后采取："<<"往前提防线，保持高压态势的战术"<<endl;
if(content == "开始防守")
cout<<name<<"收到："<<content<<"的指令，然后采取："<<"龟缩到禁区附近，进行全力防守的战术"<<endl;
}
int main()
{
CoachCommand *Kolpp;
Forward *Salah,*Mane;
Guard *vanDijk,*Matip;
Kolpp = new CoachCommand();
Salah = new Forward("萨拉赫",Kolpp);
Mane = new Forward("大马内",Kolpp);
vanDijk = new Guard("范戴克",Kolpp);
Matip = new Guard("马蒂普",Kolpp);
Kolpp->attach(Salah);
Kolpp->attach(Mane);
Kolpp->attach(vanDijk);
Kolpp->attach(Matip);
Kolpp->notify("开始强攻");
cout<<"比赛进行到75分钟，利物浦已经3:0领先！"<<endl;
Kolpp->detach(vanDijk);
Kolpp->notify("开始防守");
delete Matip;
delete vanDijk;
delete Mane;
delete Salah;
delete Kolpp;
};
