c++ - 设计问题 - 多重继承，C++

Question

首先我将展示一些代码，然后对问题进行描述:

class CGUIObject
{
protected:
    int m_id;
    bool m_bVisible;

    // Other non-relevant fields and methods specific for gui object...
};

class CClickable
{
private:
    bool m_bClicked;
public:
    bool isClicked();
    void setClicked(bool bClicked);

    virtual bool wasClicked(const TPoint& clickPos) = 0;

    // Other non-relevant fields and methods specific for clickable object...
};

class CComponent : public CGUIObject
{
    // The only important part of this class is that it derives from CGUIObject
};    

class CButton : public CComponent, CClickable
{
    // The only important part of this class is that it derives from CComponent and CClickable
};

// Now there is a method in my EventManager which informs all clickables about left mouse click event
void CEventManager::lMouseButtonClickEvent(const CPoint& clickPos)
{
    // Go through all clickables
    for(unsigned int i = 0; i < m_clickableObjectsList.size(); i++)
    {
         TClickable* obj = m_clickableObjectsList[i];

         // Here I would like to also check if obj is visible
         if(obj->wasClicked(clickPos))
         {
          obj->setClicked(true);
          if(obj->m_pOnClickListener != nullptr)
               obj->m_pOnClickListener->onClick();
         return; // Only one object can be clicked at once
         }
    }
}

好的，正如您所看到的:

• CButton 派生自 CComponent 和 CClickable
• CComponent 派生自 CGUIObject
• CGUIObject 有 m_bVisible 字段，这对我来说很重要
• 在 EventManager 中，我创建了 CClickable* 对象的列表

现在我想通知被单击的特定 CClickable 对象，但仅当它可见时。我知道所有可点击对象也都派生自 CGUIObject(例如 CButton)，但它是 CClickable* 列表，因此可以理解我无法访问 m_bVisible 字段。我知道这只是表明我在设计中犯了一个错误，但是有没有办法以某种优雅而简单的方式解决这个问题？

Answer 1

如果您知道所有可点击对象均派生自CGUIObject，则可以使用dynamic_cast:

CClickable* obj = m_clickableObjectsList[i];

// Here I would like to also check if obj is visible
if(obj->wasClicked(clickPos) && dynamic_cast<CGUIObject*>(obj)->m_bVisible)
{
  //...

如果可点击对象不是 GUI 对象，在这种情况下，dynamic_cast 将返回空指针，您应该在取消引用结果之前检查这一点。