Observer(观察者模式)

某个对象可以被设置为是可观察的，只要通过某种方式允许其他对象注册为观察者。每当被观察的对象改变时，会发送信息给观察者。

<?php
 
interface Observer {
  function onChanged($sender, $args);
}
 
interface Observable {
  function addObserver($observer);
}
 
class CustomerList implements Observable {
  private $_observers = array();
 
  public function addCustomer($name) {
    foreach($this->_observers as $obs)
      $obs->onChanged($this, $name);
  }
 
  public function addObserver($observer) {
    $this->_observers []= $observer;
  }
}
 
class CustomerListLogger implements Observer {
  public function onChanged($sender, $args) {
    echo( "'$args' Customer has been added to the list \n" );
  }
}
 
$ul = new UserList();
$ul->addObserver( new CustomerListLogger() );
$ul->addCustomer( "Jack" );