【C++】【设计模式】外观模式

【C++】【设计模式】外观模式(Facade Pattern)

定义

• 结构型模式

• 外观模式(Facade Pattern)：
  提供了一个简化的接口，用来访问复杂子系统中的一组接口。它隐藏了系统的复杂性，使客户端与子系统的交互更加简单和易用。

• 外观类

• 子系统类

UML 类图

Demo

#include <iostream>
#include <string>

// 播放器基类
class Player {
public:
    virtual void on() = 0;
    virtual void off() = 0;
    virtual void play(std::string) = 0;
    virtual void stop() = 0;
    virtual ~Player() {}
};

// DVD 播放器
class DvdPlayer : public Player {
public:
    void on() override {
        std::cout << "DvdPlayer is on." << std::endl;
    }
    void off() override {
        std::cout << "DvdPlayer is off." << std::endl;
    }
    void play(std::string movie) override {
        std::cout << "Playing " << movie << " on DvdPlayer." << std::endl;
    }
    void stop() override {
        std::cout << "DvdPlayer is stopped." << std::endl;
    }
};

// 投影仪
class Projector {
public:
    void on() {
        std::cout << "Projector is on." << std::endl;
    }
    void off() {
        std::cout << "Projector is off." << std::endl;
    }
};

// 灯光
class Light {
public:
    void on() {
        std::cout << "Light is on." << std::endl;
    }
    void off() {
        std::cout << "Light is off." << std::endl;
    }
};

// 家庭影院外观类
class HomeTheaterFacade {
private:
    DvdPlayer dvdPlayer_;
    Projector projector_;
    Light light_;
public:
    HomeTheaterFacade(DvdPlayer dvdPlayer, Projector projector, Light light) :
        dvdPlayer_(dvdPlayer), projector_(projector), light_(light) {}
    void watchMovie(std::string movie) {
        std::cout << "Get ready to watch a movie..." << std::endl;
        light_.off();
        projector_.on();
        dvdPlayer_.on();
        dvdPlayer_.play(movie);
    }
    void endMovie() {
        std::cout << "Shutting movie theater down..." << std::endl;
        light_.on();
        projector_.off();
        dvdPlayer_.stop();
        dvdPlayer_.off();
    }
};

int main() {
    DvdPlayer dvdPlayer;
    Projector projector;
    Light light;

    HomeTheaterFacade homeTheater(dvdPlayer, projector, light);
    homeTheater.watchMovie("The Matrix");
    homeTheater.endMovie();

    return 0;
}

分析与总结

• 简化客户端的操作：通过外观模式，客户端可以用一个简洁的接口来与子系统进行交互，而不必了解子系统的细节。
• 减低客户端与子系统的耦合：客户端只依赖外观类，而外观类负责与子系统的具体实现打交道。
• 提高灵活性和可维护性：子系统内部的变化不会影响到客户端，客户端只需与外观类交互，代码的维护和扩展更加灵活