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);
        }
    }
};

一、正文标题

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;

};

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