设计模式系列3-----C++实现命令模式(Command Pattern)

什么是命令模式？

GoF的书的定义为：“Command pattern encapsulate request as an object, thereby letting you parameterize clients with different request, queue or log request, and support undoable operations”

换言之，讲命令封装成一个对象，既有状态也能执行动作，发出命令者不需要知道命令最终是谁执行的，如何执行，它只依赖抽象。而且调用者可以根据命令纪录，维护一个命令队列，或者log所有的命令。命令模式也可以方便的实现撤销操作。

类图结构：

Example：

例子模拟游戏里给人发出移动和跳的命令，Player对应于类图里面的Receiver，代码如下。

#include <iostream>
using namespace std;class Player
{
public:void move(int x, int y){cout << "player move to (" << x << ", " << y << ")" << endl;}void jump(){cout << "player jump" << endl;}
};class Command
{
public:virtual void execute() = 0;
};class MoveCommand : public Command
{
public:MoveCommand(Player* pPlayer, int x, int y): m_pPlayer(pPlayer), m_intX(x), m_intY(y) { }virtual void execute(){if (m_pPlayer)m_pPlayer->move(m_intX, m_intY);}private:Player* m_pPlayer;int m_intX, m_intY;
};class JumpCommand : public Command
{
public:JumpCommand(Player* pPlayer) : m_pPlayer(pPlayer) {}virtual void execute(){if (m_pPlayer)m_pPlayer->jump();}private:Player* m_pPlayer;
};class Invoker
{
public:void takeOrder(Command* pCommand){pCommand->execute();delete pCommand;}
};int main()
{Player* pPlayer = new Player();Invoker invoker;char orderType;while (cin >> orderType){int x, y;if (orderType == 'm' && cin >> x >> y)invoker.takeOrder(new MoveCommand(pPlayer, x, y));else if (orderType == 'j')invoker.takeOrder(new JumpCommand(pPlayer));}delete pPlayer;return 0;
}

可以对Invoker修改使它支持命令队列的功能，使它包一个装命令的容器，当里面有命令的时候取出来执行。

参考资料：

PatternCraft – Command Pattern（非常好！）

<<Head First Design Pattern>>

<<Design Patterns—Elements of Reusable Object-Oriented Software>>

转载于:https://www.cnblogs.com/graphicsme/archive/2011/12/06/2278634.html