设计模式：装饰模式（c++实现案例）

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装饰模式

装饰（ Decorator ）模式又叫做包装模式。通过一种对客户端透明的方式来扩展对象的功能，是继承关系的一个替换方案。 装饰模式就是把要添加的附加功能分别放在单独的类中，并让这个类包含它要装饰的对象，当需要执行时，客户端就可以有选择地、按顺序地使用装饰功能包装对象。

装饰模式可以动态的给一个对象添加一些额外的职责。就增加功能来说，此模式比生成子类更为灵活,通过子类继承的方式，但是如果后续继续增加功能的话，便要继续继承现有的类，如此就会使继承的层次越来越深，不利与代码的维护和可读性。故最好的方式便是通过装饰者模式来完成。

装饰模式实现步骤

1.提供一个抽象组件类:抽象被装饰者的行为

2.提供一个或多个具体组件类:被装饰者的行为具体实现

3.提供一个抽象装饰器类：抽象组件指针与抽象组件一致接口

4.提供一个具体的装饰器类：为具体组件附加责任

//1. 抽象组件类，修饰被装饰者的行为
class AbstractSubject
{
public:
	virtual void show() = 0;
	string str;
};
 
//2. 具体组件类，实现被装饰的行为
class User :public AbstractSubject
{
public:
	User()
	{
		this->str = "英雄初始化  ";
	}
	void show()override
	{
		cout << this->str << endl;
	}
	
};
 
//3. 抽象装饰器
class AbstractDecrote :public AbstractSubject
{
public:
	virtual void show() = 0;
protected:
	AbstractSubject* pBase;//具有一个抽象组件指针
};
 
//4. 具体的装饰器类：为具体的组件添加责任
//装饰器1 
class DecroteUser1 :public AbstractDecrote
{
public:
	DecroteUser1(AbstractSubject* user)
	{
		this->pBase = user;//为抽象组件添加指定的具体组件
	}
	void show()override
	{
		this->str = this->pBase->str + "英雄之铠甲";
		cout << this->str << endl;
	}
};
 
//装饰器2
class DecroteUser2 :public AbstractDecrote
{
public:
	DecroteUser2(AbstractSubject* user)
	{
		this->pBase = user;//为抽象组件添加指定的具体组件
	}
	void show()override
	{
		this->str = this->pBase->str + "英雄之护膝";
		cout << this->str << endl;
	}
};
 
int main()
{
	User* me = new User;
	me->show();
	
    //穿铠甲
	DecroteUser1* pme1 = new DecroteUser1(me);
	pme1->show();
 
    //穿护膝
	DecroteUser2* pme2 = new DecroteUser2(me);
	pme2->show();
 
    //传铠甲和护膝
	DecroteUser2* pme3 = new DecroteUser2(pme1);
	pme3->show();
 
	delete me;
	delete pme1;
	delete pme2;
	delete pme3;
	return 0;
}

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优点

• 易于扩展对象功能
• 通过装饰类的排列组合，可创造出很多不同行为的组合

缺点

• 会出现更多的代码，更多的类，增加程序复杂性