C++ 中介者模式讲解和代码示例
中介者是一种行为设计模式， 让程序组件通过特殊的中介者对象进行间接沟通， 达到减少组件之间依赖关系的目的。
中介者能使得程序更易于修改和扩展， 而且能更方便地对独立的组件进行复用， 因为它们不再依赖于很多其他的类。
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流行度：
使用示例： 中介者模式在 C++ 代码中最常用于帮助程序 GUI 组件之间的通信。 在 MVC 模式中， 控制器是中介者的同义词。
概念示例
本例说明了中介者设计模式的结构并重点回答了下面的问题：
- 它由哪些类组成？
- 这些类扮演了哪些角色？
- 模式中的各个元素会以何种方式相互关联？
main.cc: 概念示例
#include <iostream> #include <string> /** * The Mediator interface declares a method used by components to notify the * mediator about various events. The Mediator may react to these events and * pass the execution to other components. */ class BaseComponent; class Mediator { public: virtual void Notify(BaseComponent *sender, std::string event) const = 0; }; /** * The Base Component provides the basic functionality of storing a mediator's * instance inside component objects. */ class BaseComponent { protected: Mediator *mediator_; public: BaseComponent(Mediator *mediator = nullptr) : mediator_(mediator) { } void set_mediator(Mediator *mediator) { this->mediator_ = mediator; } }; /** * Concrete Components implement various functionality. They don't depend on * other components. They also don't depend on any concrete mediator classes. */ class Component1 : public BaseComponent { public: void DoA() { std::cout << "Component 1 does A.\n"; this->mediator_->Notify(this, "A"); } void DoB() { std::cout << "Component 1 does B.\n"; this->mediator_->Notify(this, "B"); } }; class Component2 : public BaseComponent { public: void DoC() { std::cout << "Component 2 does C.\n"; this->mediator_->Notify(this, "C"); } void DoD() { std::cout << "Component 2 does D.\n"; this->mediator_->Notify(this, "D"); } }; /** * Concrete Mediators implement cooperative behavior by coordinating several * components. */ class ConcreteMediator : public Mediator { private: Component1 *component1_; Component2 *component2_; public: ConcreteMediator(Component1 *c1, Component2 *c2) : component1_(c1), component2_(c2) { this->component1_->set_mediator(this); this->component2_->set_mediator(this); } void Notify(BaseComponent *sender, std::string event) const override { if (event == "A") { std::cout << "Mediator reacts on A and triggers following operations:\n"; this->component2_->DoC(); } if (event == "D") { std::cout << "Mediator reacts on D and triggers following operations:\n"; this->component1_->DoB(); this->component2_->DoC(); } } }; /** * The client code. */ void ClientCode() { Component1 *c1 = new Component1; Component2 *c2 = new Component2; ConcreteMediator *mediator = new ConcreteMediator(c1, c2); std::cout << "Client triggers operation A.\n"; c1->DoA(); std::cout << "\n"; std::cout << "Client triggers operation D.\n"; c2->DoD(); delete c1; delete c2; delete mediator; } int main() { ClientCode(); return 0; } Output.txt: 执行结果
Client triggers operation A. Component 1 does A. Mediator reacts on A and triggers following operations: Component 2 does C. Client triggers operation D. Component 2 does D. Mediator reacts on D and triggers following operations: Component 1 does B. Component 2 does C. 
