PHP デザイン パターン: フレームワークとの統合

<?php

class Database {

    private static $instance;

    private function __construct() {}

    public static function getInstance() {
        if (!isset(self::$instance)) {
            self::$instance = new Database();
        }

        return self::$instance;
    }
}

$db1 = Database::getInstance();
$db2 = Database::getInstance();

var_dump($db1 === $db2); // true

<?php

interface Observer {
    public function update($subject);
}

class Subject {

    private $observers = [];

    public function attach(Observer $observer) {
        $this->observers[] = $observer;
    }

    public function detach(Observer $observer) {
        $index = array_search($observer, $this->observers);

        if ($index !== false) {
            unset($this->observers[$index]);
        }
    }

    public function notify() {
        foreach ($this->observers as $observer) {
            $observer->update($this);
        }
    }
}

class MyObserver implements Observer {

    public function update(Subject $subject) {
        // 处理主题状态的变化
    }
}

$subject = new Subject();
$observer1 = new MyObserver();
$observer2 = new MyObserver();

$subject->attach($observer1);
$subject->attach($observer2);

$subject->notify(); // 会调用观察者的 update() 方法