行为型设计模式 - 观察者 (发布订阅) Observer
作者：菜皮日记
- 2023-09-08 北京
本文字数：1506 字
阅读完需：约 5 分钟
简介
也叫做发布/订阅模式，多个观察者可订阅一个主题对象，当主题状态发生变化时会通知所有已订阅的观察者，观察者可自由处理。
角色
Subject/Publisher 主题/发布者
维护已订阅的观察者
通知已订阅的观察者
抽象 Subscribe 订阅者
定义订阅者接口
具体 Subscribe 订阅者
实现订阅者通用接口，并实现各自逻辑
类图
类图
代码
class Subject implements \SplSubject{ public $state;
private $observers;
public function __construct() { $this->observers = new \SplObjectStorage(); }
public function attach(\SplObserver $observer): void { echo "Subject: Attached an observer.\n"; $this->observers->attach($observer); }
public function detach(\SplObserver $observer): void { $this->observers->detach($observer); echo "Subject: Detached an observer.\n"; }
public function notify(): void { echo "Subject: Notifying observers...\n"; foreach ($this->observers as $observer) { $observer->update($this); } }
public function someBusinessLogic(): void { echo "\nSubject: I'm doing something important.\n"; $this->state = rand(0, 10);
echo "Subject: My state has just changed to: {$this->state}\n"; $this->notify(); }}
class ConcreteObserverA implements \SplObserver{ public function update(\SplSubject $subject): void { if ($subject->state < 3) { echo "ConcreteObserverA: Reacted to the event.\n"; } }}
class ConcreteObserverB implements \SplObserver{ public function update(\SplSubject $subject): void { if ($subject->state == 0 || $subject->state >= 2) { echo "ConcreteObserverB: Reacted to the event.\n"; } }}$subject = new Subject();
$o1 = new ConcreteObserverA();$subject->attach($o1);
$o2 = new ConcreteObserverB();$subject->attach($o2);
$subject->someBusinessLogic();$subject->someBusinessLogic();
$subject->detach($o2);
$subject->someBusinessLogic();
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output:
Subject: Attached an observer.Subject: Attached an observer.
Subject: I'm doing something important.Subject: My state has just changed to: 2Subject: Notifying observers...ConcreteObserverA: Reacted to the event.ConcreteObserverB: Reacted to the event.
Subject: I'm doing something important.Subject: My state has just changed to: 0Subject: Notifying observers...ConcreteObserverA: Reacted to the event.ConcreteObserverB: Reacted to the event.Subject: Detached an observer.
Subject: I'm doing something important.Subject: My state has just changed to: 8Subject: Notifying observers...
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