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 " ); } } $ul = new UserList(); $ul->addObserver( new CustomerListLogger() ); $ul->addCustomer( "Jack" );