命令模式(Command)

命令模式：将“请求”封装成对象，以便使用不同的请求，队列或者日志来参数化其他对象。支持可撤销操作。

要点：
1.命令模式将发出请求的对象和执行请求的对象解耦
2.在被解耦的两者之间是通过命令对象进行沟通的。命令对象封装了接收者和一个或一组动作
3.调用者通过调用命令对象的execute()发出请求，这会使得接收者的动作被调用
4.调用者可以接收命令当做参数，甚至在运行时动态地进行
5.命令可以支持撤销，做法是实现一个undo方法来回到execute()被执行前的状态
6.宏命令是命令的一种简单的延伸，允许调用多个命令。宏方法也可以支持撤销
7.实际操作时，很常见使用“聪明”命令对象，也就是直接实现了请求，而不是将工作委托给接收者
8.命令也可以用来实现日志和事务系统




Command.h

#ifndef COMMAND_H
#define COMMAND_H
#include "Properties.h"
class Command{
public:
    virtual void execute(){}
    virtual void undo(){}
};

class PowerOnCommand:public Command{
private:
    Power* mPower;
public:
    explicit PowerOnCommand(Power* power){
        mPower = power;
    }
    void execute(){
        mPower->on();
    }
    void undo(){
        mPower->off();
    }
};

class PowerOffCommand:public Command{
private:
    Power* mPower;
public:
    explicit PowerOffCommand(Power* power){
        mPower = power;
    }
    void execute(){
        mPower->off();
    }
    void undo(){
        mPower->on();
    }
};

class VolumeIncreaseCommand:public Command{
private:
    Volume* mVolume;
public:
    explicit VolumeIncreaseCommand(Volume* volume){
        mVolume = volume;
    }
    void execute(){
        mVolume->increase();
    }
    void undo(){
        mVolume->decrease();
    }
};

class VolumeDecreaseCommand:public Command{
private:
    Volume* mVolume;
public:
    explicit VolumeDecreaseCommand(Volume* volume){
        mVolume = volume;
    }
    void execute(){
        mVolume->decrease();
    }
    void undo(){
        mVolume->increase();
    }
};

#endif // COMMAND_H

Properties.h

#ifndef PROPERTIES_H
#define PROPERTIES_H
#include <iostream>
using namespace std;

class Power{
public:
    void on(){
        cout << "power on!" << endl;
    }
    void off(){
        cout << "power off!" << endl;
    }
};

class Volume{
public:
    void increase(){
        cout << "volumn increase" << endl;
    }
    void decrease(){
        cout << "volumn decrease" << endl;
    }
};

#endif // PROPERTIES_H

RemoteControl.h

#ifndef REMOTECONTROL_H
#define REMOTECONTROL_H
#include "Command.h"
class RemoteControl{
private:
    Command* mCmd;
public:
    RemoteControl(){
        mCmd = new Command;
    }
    void setCommand(Command* cmd){
        mCmd = cmd;
    }
    void pressed(){
        mCmd->execute();
    }
    void undoCmd(){
        mCmd->undo();
    }
};

#endif // REMOTECONTROL_H

#include "RemoteControl.h"
#include "Command.h"

int main()
{
    RemoteControl* rc = new RemoteControl;
    PowerOnCommand* pon = new PowerOnCommand(new Power);
    rc->setCommand(pon);
    rc->pressed();
    rc->undoCmd();
}

power on!
power off!