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中介者

中介者在 C++ 中的实现

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

在 C++ 中使用模式

复杂度

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.

中介者在其他编程语言中的实现

中介者在 Java 中的实现 中介者在 C# 中的实现 中介者在 PHP 中的实现 中介者在 Python 中的实现 中介者在 Ruby 中的实现 中介者在 Swift 中的实现 中介者在 TypeScript 中的实现