Médiateur en C++
Le Médiateur est un patron de conception comportemental qui diminue le couplage entre les composants d’un programme, en les faisant communiquer indirectement, via un objet médiateur spécial.
Le médiateur rend la modification, l’extension et la réutilisation de composants individuels aisées, car ils ne dépendent plus d’une dizaine de classes.
Complexité :
Popularité :
Exemples d’utilisation : Le médiateur est le plus souvent utilisé en C++ pour faciliter les communications entre les composants de l’interface graphique d’une application. Le contrôleur du modèle MVC est le synonyme du médiateur.
Exemple conceptuel
Dans cet exemple, nous allons voir la structure du Médiateur. Nous allons répondre aux questions suivantes :
- Que contiennent les classes ?
- Quels rôles jouent-elles ?
- Comment les éléments du patron sont-ils reliés ?
main.cc: Exemple conceptuel
#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: Résultat de l’exécution
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.
