观察者设计模式问题(observer design pattern question)

 我正在PHP中创建一个oop系统，并希望在其中实现更多的观察者模式，因为我希望减少我的类之间的重度耦合。 
 
 我的问题是这个。 关于这种模式的设计的最佳实践，一个类可以将观察者添加到该类正在使用的另一个类。 或者我应该让观察者加入到链条的最高层？ 
 
 示例:(假设其他方法被调用但未包含在类中，但对于此示例而言并不重要。） 
 
class orderItem extends observable {
     public function pick($qty, $user){
          $this->setUser($user);
          $position = new position($this->getPositionID());
          $position->addObserver(new ProductObserver());  // is this the best option ? ?
          $position->setQty($position->getQty() - $qty);
          $position->save();
          $this->notify(self::EVENT_PICK); // notify observers
     }
}

class orderProductObserver implements observer {
     public function update($orderitem){
           $position = new position($orderitem->getPositionID());
           $product = new product($position->getProductID());
           if($product->getQty() < $product->getMinimum()) {
                $alert = new minProductAlert($product);
           }
     }
}

class ProductObserver implements observer {
     public function update($position){
           $product = new product($position->getProductID());
           if($product->getQty() < $product->getMinimum()) {
                $alert = new minProductAlert($product);
           }
     }
}

$order = new orderItem(123);
$order->addObserver(new orderProductObserver()); // or is this the best option ??
$order->pick(2, 'bill');
 
 或者如果两种方法都错了，我对你的输入很感兴趣。 
 
 通过消除orderitem和position之间的依赖关系，这个例子是最理想的吗？ 
 
 class OrderItem extends Observable {
         public function pick($qty, $user){
              $this->setUser($user);
              $this->setPickedQty($qty);
              $this->save();
              $this->notify(self::EVENT_PICK); // notify observers
         }
    }

    class OrderItemPickObserver implements Observer {
         public function update($orderitem){
               $position = new Position($orderitem->getPositionID());
               $position->addObserver(new ProductPositionObserver());
               $position->setQty($position->getQty() - $orderItem->getPickedQty());
               $position->save();
         }
    }

    class ProductPositionObserver implements Observer {
         public function update($position){
               $product = new product($position->getProductID());
               if($product->getQty() < $product->getMinimum()) {
                    $alert = new minProductAlert($product);
               }
         }
    }
    $pickQty = 2;
    $orderitem = new OrderItem(123);
    $position = new Position($orderitem->getPositionID());
    if($position->getQty() >= $pickQty)
    {
           $orderitem->addObserver(new OrderItemPickObserver()); // or is this the best option ??
           $orderitem->pick($pickQty, 'bill');
    }

i am creating a oop system in php and would like to implement more observer patterns into it as i have heavy coupling between my classes that i wish to reduce.
 
my question is this. in relation to best practice in design for this pattern is it ok for one class to add an observer to another class, that class is working with. or should i keep the observer adding to the top most level of the chain?
 
example: (assume other methods called, but not included in the class, exist but are not important for this example.)
 
class orderItem extends observable {
     public function pick($qty, $user){
          $this->setUser($user);
          $position = new position($this->getPositionID());
          $position->addObserver(new ProductObserver());  // is this the best option ? ?
          $position->setQty($position->getQty() - $qty);
          $position->save();
          $this->notify(self::EVENT_PICK); // notify observers
     }
}

class orderProductObserver implements observer {
     public function update($orderitem){
           $position = new position($orderitem->getPositionID());
           $product = new product($position->getProductID());
           if($product->getQty() < $product->getMinimum()) {
                $alert = new minProductAlert($product);
           }
     }
}

class ProductObserver implements observer {
     public function update($position){
           $product = new product($position->getProductID());
           if($product->getQty() < $product->getMinimum()) {
                $alert = new minProductAlert($product);
           }
     }
}

$order = new orderItem(123);
$order->addObserver(new orderProductObserver()); // or is this the best option ??
$order->pick(2, 'bill');
 
Or alternatively if both methods are wrong i am very interested in your input.
 
would this example be the most ideal by removing dependency between orderitem and position ?
 
 class OrderItem extends Observable {
         public function pick($qty, $user){
              $this->setUser($user);
              $this->setPickedQty($qty);
              $this->save();
              $this->notify(self::EVENT_PICK); // notify observers
         }
    }

    class OrderItemPickObserver implements Observer {
         public function update($orderitem){
               $position = new Position($orderitem->getPositionID());
               $position->addObserver(new ProductPositionObserver());
               $position->setQty($position->getQty() - $orderItem->getPickedQty());
               $position->save();
         }
    }

    class ProductPositionObserver implements Observer {
         public function update($position){
               $product = new product($position->getProductID());
               if($product->getQty() < $product->getMinimum()) {
                    $alert = new minProductAlert($product);
               }
         }
    }
    $pickQty = 2;
    $orderitem = new OrderItem(123);
    $position = new Position($orderitem->getPositionID());
    if($position->getQty() >= $pickQty)
    {
           $orderitem->addObserver(new OrderItemPickObserver()); // or is this the best option ??
           $orderitem->pick($pickQty, 'bill');
    }

原文：https://stackoverflow.com/questions/7568660