Multiple Inheritance problems when inheriting from QGraphicsPolygonItem and QObject

I have a QGraphicsViewScene that displays a few QGraphicsPolygonItems. I created a class called DiagramItem that is based on QgraphicsPolygonItems. I wanted each polygon item to toggle it's "state" every 10 seconds after it was created. So I added a "state" member to my DiagramItem class called "zoneState."

I saw that for a QTimer to work, it had to be a QObject. So I added QObject as one of the base classes and added the macro Q_OBJECT to the header class. Now it fails to compile. It gives me the error: "undefined reference to 'vtable for DiagramItem.' What is going on? It seems like it should be something pretty basic. Please advise!




Here is my header file "diagramitem.h"

Code:

---

#include <QTimer>
#include <QObject>
#include <QGraphicsObject>
 
#include "scribblearea.h"
 
QT_BEGIN_NAMESPACE
class QPixmap;
class QGraphicsItem;
class QGraphicsScene;
class QTextEdit;
class QGraphicsSceneMouseEvent;
class QMenu;
class QGraphicsSceneContextMenuEvent;
class QPainter;
class QStyleOptionGraphicsItem;
class QWidget;
class QPolygonF;
QT_END_NAMESPACE
 
//! [0]
class DiagramItem : public QObject, public QGraphicsPolygonItem
{
    Q_OBJECT
public:
QTimer* iTimer;
QTime*  timeValue;
 bool zoneState;
 
public:
    enum { Type = UserType + 15 };
 
    DiagramItem(ScribbleArea *scribble, QGraphicsScene *scene = 0,QGraphicsItem *parent = 0);
    QPolygonF polygon() const
        { return myPolygon; }
 
    int type() const
        { return Type;}
    void toggleState();
    bool getState();
 
    /*
public Q_SLOTS:
    void start(int msec);
    void start();
    void stop();
 
public slots:
*/
 
private:
    QPolygonF myPolygon;
 
 
};

---

Here is "diagramitem.cpp"

Code:

---

#include <QtGui>
#include <QObject>
 
#include "diagramitem.h"
 
 
//! [0]
DiagramItem::DiagramItem(ScribbleArea *scribble, QGraphicsScene *scene,QGraphicsItem *parent)
    : QGraphicsPolygonItem(parent, scene)
{
    zoneState = false;
  //  iTimer = new QTimer();
 
  /*  QTimer *timer = new QTimer();
         connect(timer, SIGNAL(timeout()), this, SLOT(toggleState()));
         timer->start(1000);
*/
 
    //QObject::connect(iTimer,SIGNAL(timeout()),scribble,SLOT(timerToggle()));
 
    QPolygon p = scribble->getPoly();
 
     myPolygon << p.point(0) << p.point(1)<< p.point(2) << p.point(3);
 
 
    setPolygon(myPolygon);
    setFlag(QGraphicsItem::ItemIsMovable, true);
    setFlag(QGraphicsItem::ItemIsSelectable, true);
    setFlag(QGraphicsItem::ItemSendsGeometryChanges, true);
}
 
//! [5]
void DiagramItem::toggleState()
{
    if(zoneState)
        zoneState = false;
    else
        zoneState = true;
}
 
bool DiagramItem::getState()
{
    return zoneState;
 
}

---

Rerun qmake. You need to do that each time you add the Q_OBJECT macro to an existing file.

Thank you, that worked. For further reading fun and limitations regarding Meta Object Compiler go here: http://doc.qt.digia.com/4.2/moc.html#limitations