简介

通过引入一个中介者，将对象之间两两交互的情景，改为每个对象都是与中介者交互，行将网状关系改成了星状关系。毛病是中介者逻辑会很臃肿。

当零碎中呈现多对多的状况时，应该先思考设计是否正当，而尽量不要间接应用中介者。

角色

  • 形象Mediator中介者
  • 具体Mediator中介者
  • 形象Component
  • 具体Component

类图

中介者须要理解所有Component，而且notify中要编写解决所有可能产生的状况，Mediator是一个十分臃肿的类。

代码

interface Mediator{    public function notify(object $sender, string $event): void;}class ConcreteMediator implements Mediator{    private $component1;    private $component2;    public function __construct(Component1 $c1, Component2 $c2)    {        $this->component1 = $c1;        $this->component1->setMediator($this);        $this->component2 = $c2;        $this->component2->setMediator($this);    }    public function notify(object $sender, string $event): void    {        if ($event == "A") {            echo "Mediator reacts on A and triggers following operations:\n";            $this->component2->doC();        }        if ($event == "D") {            echo "Mediator reacts on D and triggers following operations:\n";            $this->component1->doB();            $this->component2->doC();        }    }}class BaseComponent{    protected $mediator;    public function __construct(Mediator $mediator = null)    {        $this->mediator = $mediator;    }    public function setMediator(Mediator $mediator): void    {        $this->mediator = $mediator;    }}class Component1 extends BaseComponent{    public function doA(): void    {        echo "Component 1 does A.\n";        $this->mediator->notify($this, "A");    }    public function doB(): void    {        echo "Component 1 does B.\n";        $this->mediator->notify($this, "B");    }}class Component2 extends BaseComponent{    public function doC(): void    {        echo "Component 2 does C.\n";        $this->mediator->notify($this, "C");    }    public function doD(): void    {        echo "Component 2 does D.\n";        $this->mediator->notify($this, "D");    }}$c1 = new Component1();$c2 = new Component2();$mediator = new ConcreteMediator($c1, $c2);echo "Client triggers operation A.\n";$c1->doA();echo "\n";echo "Client triggers operation D.\n";$c2->doD();

output:

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.

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