往期地址：

• 设计模式（一）——简单工厂模式
• 设计模式（二）——策略模式

本期主题：

讲解装饰模式

装饰模式

• 1.什么是装饰模式
• 2.实例
• • 2.1 场景
  • 2.2 代码

1.什么是装饰模式

2.实例

2.1 场景

例如现在开发了业务通知系统，其中有一个通知类，通知有多种模式：email、微信、电话通知等等。

随着后来的发展，需求越来越复杂，有的通知希望既能email，又能wechat通知，这样的话，组合就越来越多。
按照我们最初的设计就是不停的增加子类，这样后期代码会十分庞大，不利于维护。

因此，我们在这里引入装饰模式。

接着讲上面的例子，就是把各种通知方法放入装饰。

2.2 代码

#include <iostream>
#include <stdlib.h>
#include <string>
using namespace std;

class Component {
    public:
        virtual string Operation() const = 0;
};

class ConcreteComponent : public Component {
    public:
        string Operation() const override {
            return "ConcreteComponent";
        }
};

class Decorator : public Component {
    protected:
        Component *component_;

    public:
        Decorator(Component* component) : component_(component) {}
        string Operation() const override {
            return this->component_->Operation();
        }
};


class ConcreteDecoratorA : public Decorator {
    public:
        ConcreteDecoratorA(Component *component) : Decorator(component) {}
        string Operation() const override {
            return "ConcreteDecoratorA(" + Decorator::Operation() + ")";
        }
};

class ConcreteDecoratorB : public Decorator {
    public:
        ConcreteDecoratorB(Component *component) : Decorator(component) {}
        string Operation() const override {
            return "ConcreteDecoratorB(" + Decorator::Operation() + ")";
        }
};

void ClientCode(Component *component)
{
    cout << "RESULT: " << component->Operation() << endl;
}

int main(void)
{
    Component *simple = new ConcreteComponent;
    cout << "Clinet: got a simple component:\n";
    ClientCode(simple);
    cout << "\n";

    Component *decorator1 = new ConcreteDecoratorA(simple);
    Component *decorator2 = new ConcreteDecoratorB(decorator1);
    cout << "Clinet: got a decorated component:\n";
    ClientCode(decorator2);
    cout << "\n";

    delete simple;
    delete decorator1;
    delete decorator2;
    return 0;

}

//输出：
Clinet: got a simple component:
RESULT: ConcreteComponent

Clinet: got a decorated component:
RESULT: ConcreteDecoratorB(ConcreteDecoratorA(ConcreteComponent))

输出是用ConcreteDecoratorB、ConcreteDecoratorA装饰的 component