游戏开发中的设计模式之一－Strategy模式

1． 定义

Strategy模式定义了算法族，分别封装起来，让它们之间可以互相替换，此模式让算法的变化独立于使用算法的客户。

2． 设计原则

找出应用中可能需要变化之处，把它们独立出来，不要和哪些不需要变化的代码混在一起

3． 实例

我们在游戏中经常看到有不同的角色，各种角色使用不同的武器，并且还可以更换武器。该问题可以抽象为如下描述：游戏角色类及武器行为类，每个角色一次只能使用一个武器，但是可以在游戏过程中更换武器。

通过分析，该应用可以使用Strategy模式解决，并给出类图如下，类图使用Rose逆向生成的，有点乱：）图片比较大，如果显示不完整，大家可以保存到本地打开看：



4. 代码实现

/*****************Strategy.h**************************/

// ***************************************************************

// Strategy version: 1.0 · date: 09/01/2008

// -------------------------------------------------------------

// Author: Wang Liuqiang

// E-mail: wlq_729@163.com

// -------------------------------------------------------------

// Copyright (C) 2008 - All Rights Reserved

// ***************************************************************

#ifndef STRATEGY_H_

#define STRATEGY_H_

class WeaponBehavior;

class Character

{

public:

Character();

Character(WeaponBehavior* pWeapon);

~Character();

void fight();

void SetWeapon(WeaponBehavior* w);

private:

WeaponBehavior* m_weapor;

};

class Queue : public Character

{

public:

Queue();

~Queue();

};

class King : public Character

{

public:

King();

~King();

};

class Troll : public Character

{

public:

Troll();

~Troll();

};

class Knight : public Character

{

public:

Knight();

~Knight();

};

class WeaponBehavior

{

public:

WeaponBehavior();

~WeaponBehavior();

virtual void useWeapon() = 0;

};

class KnifeBehvior : public WeaponBehavior

{

public:

KnifeBehvior();

~KnifeBehvior();

virtual void useWeapon();

};

class BowAndArrorBehavior : public WeaponBehavior

{

public:

BowAndArrorBehavior();

~BowAndArrorBehavior();

virtual void useWeapon();

};

class AxeBehavior : public WeaponBehavior

{

public:

AxeBehavior();

~AxeBehavior();

virtual void useWeapon();

};

class SwordBehavior : public WeaponBehavior

{

public:

SwordBehavior();

~SwordBehavior();

virtual void useWeapon();

};

#endif

/*********************Strategy.cpp*****************************/

#include "Strategy.h"

#include <iostream>

using namespace std;

Character::Character():m_weapor(NULL)

{

}

Character::Character(WeaponBehavior* pWeapon)

{

m_weapor = pWeapon;

}

Character::~Character()

{

if (m_weapor != NULL)

{

delete m_weapor;

m_weapor = NULL;

}

}

void Character::fight()

{

m_weapor->useWeapon();

}

void Character::SetWeapon(WeaponBehavior* w)

{

m_weapor = w;

}

Queue::Queue():Character(new KnifeBehvior())

{

}

Queue::~Queue()

{

}

King::King():Character(new SwordBehavior())

{

}

King::~King()

{

}

Troll::Troll():Character(new AxeBehavior())

{

}

Knight::Knight():Character(new BowAndArrorBehavior())

{

}

WeaponBehavior::WeaponBehavior()

{

}

WeaponBehavior::~WeaponBehavior()

{

}

KnifeBehvior::KnifeBehvior()

{

}

KnifeBehvior::~KnifeBehvior()

{

}

void KnifeBehvior::useWeapon()

{

cout<<"Fight use Knife!"<<endl;

}

AxeBehavior::AxeBehavior()

{

}

AxeBehavior::~AxeBehavior()

{

}

void AxeBehavior::useWeapon()

{

cout<<"Fight use Axe!"<<endl;

}

SwordBehavior::SwordBehavior()

{

}

SwordBehavior::~SwordBehavior()

{

}

void SwordBehavior::useWeapon()

{

cout<<"Fight use Sword!"<<endl;

}

BowAndArrorBehavior::BowAndArrorBehavior()

{

}

BowAndArrorBehavior::~BowAndArrorBehavior()

{

}

void BowAndArrorBehavior::useWeapon()

{

cout<<"Fight use BowAndArrow!"<<endl;

}

/********************Main.cpp****************************/

#include "Strategy.h"

void main()

{

Character* character = new King();

character->fight();

character = new Queue();

character->fight();

character = new Troll();

character->fight();

character = new Knight();

character->fight();

WeaponBehavior* pWeapon = new SwordBehavior();

character->SetWeapon(pWeapon);

character->fight();

delete character;

character = 0;

}