1 基本

<?php
interface Subject
{
    public function add(Observer $observer);
    public function del(Observer $observer);
    public function notify();
}
interface Observer
{
    public function say();
}
class ConcreteObserver implements Observer
{
    private $name ;
    public function __construct($name)
    {
        $this->name = $name;
    }
    public function say()
    {
        echo 'say '.$this->name.PHP_EOL;
    }
}
class ConcreteSubject implements Subject
{
    private $_observer;
    private $notify_times = 0;
    public function __construct()
    {
        $this->_observer = [];
    }
    public function add(Observer $observer)
    {
        return array_push($this->_observer, $observer);
    }
    public function del(Observer $observer)
    {
        $index = array_search($observer, $this->_observer);
        if ($index === false || !key_exists($index, $this->_observer)) {
            return false;
        }
        unset($this->_observer[$index]);
        return true;
    }
    public function notify()
    {
        $this->notify_times++;
        echo "开始第 $this->notify_times 次通知".PHP_EOL;;
        if (!is_array($this->_observer)) return false;
        foreach ($this->_observer as $item) {
            $item->say();
        }
        return true;
    }
}
$dog = new ConcreteObserver('dog');
$cat = new ConcreteObserver('cat');
$subject = new ConcreteSubject();
$subject->add($dog);
$subject->notify();
$subject->add($cat);
$subject->add($cat);
$subject->notify();
$subject->del($cat);
$subject->notify();
$subject->del($dog);
$subject->notify();
$subject->del($cat);
$subject->notify();