1. 例子-创建一组控制遥控器的API

2. 定义命令模式

命令模式其实就是定义一个命令接口，然后具体命令实现这个接口，只暴露出命令的接口

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。命令模式也支持可撤销操作。

3. 命令模式的更多用途

3.1 队列请求

3.2 日志请求

4. 部分源码

4.1 Command.h

class Command{
public:
    std::string name="Command";
    virtual void execute()=0;
    virtual void undo()=0;
    virtual ~Command(){};
};

4.2 CeilingFan.h

enum{OFF,LOW,MEDIUM,HIGH};
class CeilingFan{
public:
    string location;
    int speed;
    CeilingFan(string location);
    void high();
    void medium();
    void low();
    void off();
    int getSpeed();
};

4.3 CeilingFanHighCommand.h

#include "Command.h"
#include "CeilingFan.h"
class CeilingFanHighCommand:public Command{
public:
    CeilingFanHighCommand(CeilingFan *ceilingFan);
    virtual void execute()override final;
    virtual void undo()override final;
    virtual ~CeilingFanHighCommand();
private:
    CeilingFan *ceilingFan;
    int prevSpeed;
};

4.4 CeilingFanHighCommand.cpp

#include "CeilingFanHighCommand.h"

CeilingFanHighCommand::CeilingFanHighCommand(CeilingFan *ceilingFan)
{
    name="CeilingFanHighCommand";
    this->ceilingFan=ceilingFan;
}

void CeilingFanHighCommand::execute()
{
    prevSpeed=ceilingFan->getSpeed();
    ceilingFan->high();
}

void CeilingFanHighCommand::undo()
{
    if (prevSpeed == HIGH) {
        ceilingFan->high();
    } else if (prevSpeed == MEDIUM) {
        ceilingFan->medium();
    } else if (prevSpeed == LOW) {
        ceilingFan->low();
    } else if (prevSpeed == OFF) {
        ceilingFan->off();
    }
}

CeilingFanHighCommand::~CeilingFanHighCommand()
{

}

5. 总结

命令模式将发出请求的对象和执行请求的对象解耦