设计模式 05 外观模式

发布于 2021-06-12  2 次阅读


一、意图

  为子系统中的一组接口提供一个一致的界面。
  人话:外部类不再直接与系统中的具体子类交互,而是统一交由一个中间人代理完成。

二、UML

图1
图1:外观模式UML

三、实例

#include <iostream>
#include <map>
#include <memory>
class Subsystem1 {
public:
    std::string Operation1() const {
        return "Subsystem1: Ready!\n";
    }
    // ...
    std::string OperationN() const {
        return "Subsystem1: Go!\n";
    }
};

class Subsystem2 {
public:
    std::string Operation1() const {
        return "Subsystem2: Get ready!\n";
    }
    // ...
    std::string OperationZ() const {
        return "Subsystem2: Fire!\n";
    }
};

class Facade {
protected:
    Subsystem1* subsystem1_;
    Subsystem2* subsystem2_;

public:

    Facade(
        Subsystem1* subsystem1 = nullptr,
        Subsystem2* subsystem2 = nullptr)
    {
        this->subsystem1_ = this->subsystem1_ == subsystem1 ? subsystem1 : new Subsystem1;
        this->subsystem2_ = this->subsystem2_ == subsystem2 ? subsystem2 : new Subsystem2;
    }
    ~Facade() {
        delete subsystem1_;
        delete subsystem2_;
    }

    std::string Operation() {
        std::string result = "Facade initializes subsystems:\n";
        result += this->subsystem1_->Operation1();
        result += this->subsystem2_->Operation1();
        result += "Facade orders subsystems to perform the action:\n";
        result += this->subsystem1_->OperationN();
        result += this->subsystem2_->OperationZ();
        return result;
    }
};

void ClientCode(Facade* facade) {
    // ...
    std::cout << facade->Operation();
    // ...
}

int main() {
    Subsystem1* subsystem1 = new Subsystem1;
    Subsystem2* subsystem2 = new Subsystem2;
    Facade* facade = new Facade(subsystem1, subsystem2);
    ClientCode(facade);

    delete facade;

    return 0;
}