外观模式 (Facade Pattern)

外观模式 (Facade Pattern)

意图：为子系统中的一组接口提供一个一致的界面，简化使用。

基础组件

• Facade (外观)：提供简化的接口
• Subsystem Classes (子系统类)：实现子系统的功能

继承/实现关系

Facade --> SubsystemClass1, SubsystemClass2, ... (组合关系)

应用场景

• 简化复杂系统的使用
• 为子系统提供清晰入口点
• 减少系统间的耦合

C++ 实现（家庭影院场景）

#include <iostream>
#include <string>

/*
* 外观模式
* 意图：为子系统中的一组接口提供一个一致的界面，简化使用。
* 基础组件：
* - Facade (外观)：提供简化的接口
* - Subsystem Classes (子系统类)：实现子系统的功能
* 继承/实现关系：
* Facade 依赖于多个子系统类，通过它们提供的功能来实现简化的接口。
*/

// 子系统：投影仪
class Projector {
public:
    void on() { std::cout << "Projector on\n"; }
    void off() { std::cout << "Projector off\n"; }
    void setInput(const std::string& input) {
        std::cout << "Projector input set to " << input << "\n";
    }
};

// 子系统：音响系统
class SoundSystem {
public:
    void on() { std::cout << "Sound system on\n"; }
    void off() { std::cout << "Sound system off\n"; }
    void setVolume(int level) {
        std::cout << "Volume set to " << level << "\n";
    }
};

// 子系统：蓝光播放器
class BluRayPlayer {
public:
    void on() { std::cout << "Blu-ray player on\n"; }
    void off() { std::cout << "Blu-ray player off\n"; }
    void play(const std::string& movie) {
        std::cout << "Playing movie: " << movie << "\n";
    }
};

// 子系统：灯光控制器
class Lights {
public:
    void dim(int level) {
        std::cout << "Lights dimmed to " << level << "%\n";
    }
    void on() { std::cout << "Lights on\n"; }
};

// 外观：家庭影院外观
class HomeTheaterFacade {
public:
    HomeTheaterFacade(Projector* proj, SoundSystem* sound,
        BluRayPlayer* player, Lights* lights)
        : projector_(proj), sound_(sound), player_(player), lights_(lights) {}

    void watchMovie(const std::string& movie) {
        std::cout << "Get ready to watch a movie...\n";
        lights_->dim(10);
        projector_->on();
        projector_->setInput("HDMI");
        sound_->on();
        sound_->setVolume(20);
        player_->on();
        player_->play(movie);
    }

    void endMovie() {
        std::cout << "Shutting down home theater...\n";
        player_->off();
        sound_->off();
        projector_->off();
        lights_->on();
    }

private:
    Projector* projector_;
    SoundSystem* sound_;
    BluRayPlayer* player_;
    Lights* lights_;
};

void FacadePattern()
{
	std::cout << std::string(13, '-') << " Facade Pattern " << std::string(13, '-') << std::endl;

    Projector projector;
    SoundSystem sound;
    BluRayPlayer player;
    Lights lights;

    HomeTheaterFacade theater(&projector, &sound, &player, &lights);

    theater.watchMovie("Inception");
    // ... 观看电影 ...
    theater.endMovie();
}

组件对应关系

• HomeTheaterFacade → 外观
• Projector/SoundSystem/BluRayPlayer/Lights → 子系统类