[行为模式] head first 设计模式之命令模式(Command)

1 意图
  将一个请求封装为一个对象，从而使你可用不同的请求对客户进行参数化；对请求排队或记录请求日志，以及支持可撤销的操作。
  命令模式可以将"动作的请求者"从"动作的执行者"对象中解耦。

2 别名
  动作（Action） 事物（Transaction）



以前做过一个项目，类似控制台的命令，把复杂的请求和相应利用Command模式进行封装；

//////////////////////////////////////////////////////////////////////////
#include "Reciever.h"
class Reciever;

class Command
{
public:
    virtual ~Command(){}
	virtual void Excute() = 0;

protected:
    Command(){}
};

class ConcreteCommand : public Command
{
public:
    ConcreteCommand(Reciever *rev){this->_rev = rev;}
    ~ConcreteCommand(){}

    void Excute(){this->_rev->Action();}

private:
	Reciever *_rev;
};

//////////////////////////////////////////////////////////////////////////
#include <iostream>
using namespace std;

class Reciever
{
public:
    Reciever(){}
    ~Reciever(){}
	void Action()
    {
        cout << "Reciever action..."<<endl;
    }
};

//////////////////////////////////////////////////////////////////////////
#include "Command.h"
class Command;

class Invoker
{
public:
    Invoker(Command *cmd){this->_cmd = cmd;}
    ~Invoker(){}

    void Invoke(){this->_cmd->Excute();}

private:
	Command *_cmd;
};

int main(int argc, char *argv[])
{
	Reciever *rev = new Reciever();
	Command *cmd = new ConcreteCommand(rev);
	Invoker *inv = new Invoker(cmd);
	inv->Invoke();

	return 0;
}

在headfirst中采用的是遥控器的例子，具体如下：

#include <iostream>
#include <cassert>
#include <string>
using namespace std;

//命令模式
namespace Command
{

//////////////////////////////////////////////////////////////////////////
const int REMOTE_SIZE = 7;

//////////////////////////////////////////////////////////////////////////
class Light
{
public:
    Light(){}
    Light(string str){ m_Name = str;}

    void on(){ cout << m_Name.c_str() << " Light is on" << endl;}
    void off(){ cout << m_Name.c_str() << " Light is off" << endl;}

private:
    string m_Name;
};

//////////////////////////////////////////////////////////////////////////
class Command
{
public:
    virtual ~Command(){}
    virtual void execute() = 0;
    virtual char* getName() = 0;
};

//////////////////////////////////////////////////////////////////////////
class LightOnCommand : public Command
{
public:
    LightOnCommand(Light* light)
        :m_Light(NULL)
    {
        this->m_Light = light;
    }
    ~LightOnCommand()
    {
        //if (m_Light != NULL)
        //{
        //    delete m_Light;
        //}
    }

    virtual void execute()
    {
       assert(m_Light != NULL);
       m_Light->on();
    }

    virtual char* getName()
    {
        return "LightOnCommand";
    }

private:
    Light* m_Light;
};

//////////////////////////////////////////////////////////////////////////
class LightOffCommand : public Command
{
public:
    LightOffCommand(Light* light)
        :m_Light(NULL)
    {
        this->m_Light = light;
    }
    ~LightOffCommand()
    {
        if (m_Light != NULL)
        {
            delete m_Light;
        }
    }

    virtual void execute()
    {
        assert(m_Light != NULL);
        m_Light->off();
    }

    virtual char* getName()
    {
        return "LightOffCommand";
    }

private:
    Light* m_Light;
};

//////////////////////////////////////////////////////////////////////////
class Stereo
{
public:
    void on(){ cout << "Stereo::on" << endl;}
    void setCD(){ cout << "Stereo::setCD" << endl;}
    void setVolume(int vol)
    {
        cout << "Stereo::setVolume(" << vol << ")"<< endl;
    }
};

//////////////////////////////////////////////////////////////////////////
class StereoOnWithCDCommand : public Command
{
public:
    StereoOnWithCDCommand(Stereo* stereo)
        :m_Stereo(NULL)
    {
        m_Stereo = stereo;
    }
    virtual ~StereoOnWithCDCommand()
    {
        //if (m_Stereo != NULL)
        //{
        //    delete m_Stereo;
        //}
    }
    virtual void execute()
    {
        assert(m_Stereo != NULL);
        m_Stereo->on();
        m_Stereo->setCD();
        m_Stereo->setVolume(11);
    }

    virtual char* getName()
    {
        return "LightOffCommand";
    }

private:
    Stereo* m_Stereo;
};

//////////////////////////////////////////////////////////////////////////
class SimpleRemoteControl
{
public:
    SimpleRemoteControl()
        :m_Slot(NULL)
    {}
    ~SimpleRemoteControl()
    {
        //if (m_Slot != NULL)
        //{
        //    delete m_Slot;
        //}
    }
    void setCommand(Command* command)
    {
        //if (m_Slot != NULL)
        //{
        //    delete m_Slot;
        //}

        m_Slot = command;
    }
    void buttonWasPressed()
    {
        assert(m_Slot != NULL);
        m_Slot->execute();
    }

private:
    Command* m_Slot;
};

//////////////////////////////////////////////////////////////////////////
class RemoteControlTest
{
public:
    void run()
    {
        //test for simple remote control
        SimpleRemoteControl* remote = new SimpleRemoteControl();

        Light* light = new Light();
        LightOnCommand* lightOn = new LightOnCommand(light);
        remote->setCommand(lightOn);
        remote->buttonWasPressed();
        delete light;
        delete lightOn;

        Stereo* stereo = new Stereo();
        StereoOnWithCDCommand* stereoOnWithCDCommand = new StereoOnWithCDCommand(stereo);
        remote->setCommand(stereoOnWithCDCommand);
        remote->buttonWasPressed();
        delete stereo;
        delete stereoOnWithCDCommand;

        delete remote;
    }
};

}//namespace Command