关于后端:行为型设计模式中介者-Mediator

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.

本文由 mdnice 多平台公布