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                ### 觀察者模式 #### 特點: 觀察者模式(Observer),當一個對象狀態發生變化時,依賴它的對象全部會收到通知,并自動更新。觀察者模式實現了低耦合,非侵入式的通知與更新機制。 #### 應用: 一個事件發生后,要執行一連串更新操作。傳統的編程方式,就是在事件的代碼之后直接加入處理的邏輯。當更新的邏輯增多之后,代碼會變得難以維護。這種方式是耦合的,侵入式的,增加新的邏輯需要修改事件的主體代碼。 ``` // 主題接口 interface Subject{ public function register(Observer $observer); public function notify(); } // 觀察者接口 interface Observer{ public function watch(); } // 主題 class Action implements Subject{ public $_observers=[]; public function register(Observer $observer){ $this->_observers[]=$observer; } public function notify(){ foreach ($this->_observers as $observer) { $observer->watch(); } } } // 觀察者 class Cat1 implements Observer{ public function watch(){ echo "Cat1 watches TV<hr/>"; } } class Dog1 implements Observer{ public function watch(){ echo "Dog1 watches TV<hr/>"; } } class People implements Observer{ public function watch(){ echo "People watches TV<hr/>"; } } // 調用實例 $action=new Action(); $action->register(new Cat1()); $action->register(new People()); $action->register(new Dog1()); $action->notify(); ```
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