Observer code examples of PHP design pattern (27)

purpose

When the state of an object changes, all objects that depend on it are notified and automatically updated. It uses a low coupling method.

example

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note!

PHP has defined two interfaces to quickly implement the observer mode: SplObserver and SplSubject.

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Code

• User.php

<?php

namespace DesignPatterns\Behavioral\Observer;

/**
 * User 实现观察者模式 (称为主体)，它维护一个观察者列表，
 * 当对象发生变化时通知  User。
 */
class User implements \SplSubject
{
    /**
 * @var string
 */
    private $email;

    /**
 * @var \SplObjectStorage
 */
    private $observers;

    public function __construct()
    {
        $this->observers = new \SplObjectStorage();
    }

    public function attach(\SplObserver $observer)
    {
        $this->observers->attach($observer);
    }

    public function detach(\SplObserver $observer)
    {
        $this->observers->detach($observer);
    }

    public function changeEmail(string $email)
    {
        $this->email = $email;
        $this->notify();
    }

    public function notify()
    {
        /** @var \SplObserver $observer */
        foreach ($this->observers as $observer) {
            $observer->update($this);
        }
    }
}

• UserObserver.php

<?php

namespace DesignPatterns\Behavioral\Observer;

class UserObserver implements \SplObserver
{
    /**
 * @var User[]
 */
    private $changedUsers = [];

    /**
 * 它通常使用  SplSubject::notify()  通知主体
 *
 * @param \SplSubject $subject
 */
    public function update(\SplSubject $subject)
    {
        $this->changedUsers[] = clone $subject;
    }

    /**
 * @return User[]
 */
    public function getChangedUsers(): array
    {
        return $this->changedUsers;
    }
}

test

• Tests/ObserverTest.php

<?php

namespace DesignPatterns\Behavioral\Observer\Tests;

use DesignPatterns\Behavioral\Observer\User;
use DesignPatterns\Behavioral\Observer\UserObserver;
use PHPUnit\Framework\TestCase;

class ObserverTest extends TestCase
{
    public function testChangeInUserLeadsToUserObserverBeingNotified()
    {
        $observer = new UserObserver();

        $user = new User();
        $user->attach($observer);

        $user->changeEmail('[email protected]');
        $this->assertCount(1, $observer->getChangedUsers());
    }
}

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