观察者模式

<?php
 
// 主题接口
interface Subject
{
    public function attach(Observer $observer): void;
    public function detach(Observer $observer): void;
    public function notify(): void;
}
 
// 具体主题类
class ConcreteSubject implements Subject
{
    private $observers = [];
    private $state;
 
    public function attach(Observer $observer): void
    {
        $this->observers[] = $observer;
    }
 
    public function detach(Observer $observer): void
    {
        $this->observers = array_filter($this->observers, function ($o) use ($observer) {
            return $o !== $observer;
        });
    }
 
    public function notify(): void
    {
        foreach ($this->observers as $observer) {
            $observer->update($this);
        }
    }
 
    public function setState($state): void
    {
        $this->state = $state;
        $this->notify();
    }
 
    public function getState()
    {
        return $this->state;
    }
}
 
// 观察者接口
interface Observer
{
    public function update(ConcreteSubject $subject): void;
}
 
// 具体观察者类
class ConcreteObserver implements Observer
{
    private $name;
 
    public function __construct($name)
    {
        $this->name = $name;
    }
 
    public function update(ConcreteSubject $subject): void
    {
        echo "观察者 {$this->name} 已更新，新的状态是：{$subject->getState()}\n";
    }
}
 
// 客户端代码
$subject = new ConcreteSubject();
 
$observer1 = new ConcreteObserver("Observer 1");
$observer2 = new ConcreteObserver("Observer 2");
 
$subject->attach($observer1);
$subject->attach($observer2);
 
echo "设置状态为 1:\n";
$subject->setState(1);
 
echo "设置状态为 2:\n";
$subject->setState(2);
 
$subject->detach($observer1);
 
echo "设置状态为 3:\n";
$subject->setState(3);