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class ObjectRelationship{
protected:
    ObjectRelationship(){}

public:
    virtual ~ObjectRelationship(){}

private:
    ObjectRelationship(const ObjectRelationship&);
    ObjectRelationship& operator =(const ObjectRelationship&);

public:
    bool CreateRelationship(ObjectRelationship* pObject)
    {
        if (!DoCreateRelationship_(pObject))
        {
            return false;
        }
        RelationshipCreated_(pObject);
        return true;
    }
    bool DestroyRelationship(ObjectRelationship* pObject)
    {
        if (!DoDestroyRelationship_(pObject))
        {
            return false;
        }
        RelationshipDestroyed_(pObject);
        return true;
    }

protected:
    virtual bool DoCreateRelationship_(ObjectRelationship* /*pObject*/) = 0;
    virtual bool DoDestroyRelationship_(ObjectRelationship* /*pObject*/) = 0;

protected:
    virtual void RelationshipCreated_(ObjectRelationship* /*pObject*/){}
    virtual void RelationshipDestroyed_(ObjectRelationship* /*pObject*/){}
};

class LayoutChildren;

typedef std::set<LayoutChildren*> LayoutChildrenSet;

class RelatedObject{
    Widget* pWidget_; // 控件

    // 控件所關聯的對象
    LayoutChildrenSet layoutChildrens_; // 可以有多個布局管理管理不同的子控件布局

private:
    friend class Widget;
    explicit RelatedObject(Widget* const pWidget);

public: // 獲取關聯對象的接口
    const LayoutChildrenSet& GetLayoutChildrens() const{return layoutChildrens_;}

private:
    void RelationshipCreated_(ObjectRelationship* pObject);
    void RelationshipDestroyed_(ObjectRelationship* pObject);
};

void Widget::RelationshipCreated_(ObjectRelationship* pObject)
{
    GetRelatedObject()->RelationshipCreated_(pObject);
}
void Widget::RelationshipDestroyed_(ObjectRelationship* pObject)
{
    GetRelatedObject()->RelationshipDestroyed_(pObject);
}

void Widget::LayoutChildren()
{
    auto pRelatedObject = GetRelatedObject();
    if (pRelatedObject)
    {
        const widget::LayoutChildrenSet& layoutChildrens = pRelatedObject->GetLayoutChildrens();
        std::for_each(
            layoutChildrens.begin(), layoutChildrens.end(), 
            std::bind(std::mem_fn(&widget::LayoutChildren::Layout), std::placeholders::_1, this));
    }
}