regarding qgraphicsitem_cast

[Gopala Krishna]

Hello guys,
I am facing some problems with qgraphicsitem_cast which casts in a wrong manner resulting in crashes.
Because of this now I am forced to check manually the value of type() function and then cast.
I am using Qt4.2.2 on linux.

The following working example illustrates my problem.
Is there something wrong in my code or is it a Qt bug ??

#include <QtGui>
 
class Item : public QGraphicsItem
{
public:
    enum ItemTypes {
         ItemType = UserType+5,
         ComponentType,
         WireType,
      };
 
      Item() : QGraphicsItem(0,0) { }
 
      QRectF boundingRect() const { return QRectF(-20,-20,40,40); }
 
      void paint(QPainter *p,const QStyleOptionGraphicsItem *, QWidget *)
      {
             p->drawLine(-20,-20,20,20);
      }
      int type() const { return ItemType; }
};
 
class Component : public Item
{
public:
    int type() const { return Item::ComponentType; }
};
 
class Resistor : public Component
{
};
 
 
class Wire : public Component
{
public:
    int type() const { return Item::WireType; }
};
 
int main(int argc,char *argv[])
{
   QApplication app(argc,argv);
   QGraphicsScene sc(0,0,500,500);
 
   Resistor * r= new Resistor();
 
   sc.addItem(r);
   r->setPos(50,50);
   QGraphicsView v;
   v.setScene(&sc);
   v.show();
 
  // The problematic part
   Wire *w = qgraphicsitem_cast<Wire*>(r);
   if(w != 0l) // this always happens
   {
           qDebug("WRONGLY CASTED");
           Q_ASSERT(0);
   }
 
   return app.exec();
};

#include <QtGui>

class Item : public QGraphicsItem
{
public:
    enum ItemTypes {
         ItemType = UserType+5,
         ComponentType,
         WireType,
      };

      Item() : QGraphicsItem(0,0) { }

      QRectF boundingRect() const { return QRectF(-20,-20,40,40); }

      void paint(QPainter *p,const QStyleOptionGraphicsItem *, QWidget *)
      {
             p->drawLine(-20,-20,20,20);
      }
      int type() const { return ItemType; }
};

class Component : public Item
{
public:
    int type() const { return Item::ComponentType; }
};

class Resistor : public Component
{
};


class Wire : public Component
{
public:
    int type() const { return Item::WireType; }
};

int main(int argc,char *argv[])
{
   QApplication app(argc,argv);
   QGraphicsScene sc(0,0,500,500);

   Resistor * r= new Resistor();

   sc.addItem(r);
   r->setPos(50,50);
   QGraphicsView v;
   v.setScene(&sc);
   v.show();

  // The problematic part
   Wire *w = qgraphicsitem_cast<Wire*>(r);
   if(w != 0l) // this always happens
   {
           qDebug("WRONGLY CASTED");
           Q_ASSERT(0);
   }
 
   return app.exec();
};

To copy to clipboard, switch view to plain text mode 

I checked the source of qgraphicsitem_cast but I couldn't understand how it works. Can somebody enligten me ?

template <class T> inline T qgraphicsitem_cast(QGraphicsItem *item)
{
    return int(static_cast<T>(0)->Type) == int(QGraphicsItem::Type)
        || (item && int(static_cast<T>(0)->Type) == item->type()) ? static_cast<T>(item) : 0;
}

template <class T> inline T qgraphicsitem_cast(QGraphicsItem *item)
{
    return int(static_cast<T>(0)->Type) == int(QGraphicsItem::Type)
        || (item && int(static_cast<T>(0)->Type) == item->type()) ? static_cast<T>(item) : 0;
}

To copy to clipboard, switch view to plain text mode