Qt undefined reference vtable - c++

Question

I made simple game to shot rectangle(class Bullet) from other rectangle(class MyRect). I have error undefined reference to 'vtable for bullet'. I have written that is connected with Q_OBJECT and moc.I can't resolve this problem.
Bullet.h
#ifndef BULLET_H
#define BULLET_H
#ifndef Q_MOC_RUN
#include <QGraphicsRectItem>
#include <QObject>
class Bullet: public QObject,public QGraphicsRectItem{
Q_OBJECT
public:
Bullet();
public slots:
void move();
};
#endif
#endif // BULLET_H
MyRect.h
#ifndef MYRECT_H
#define MYRECT_H
#include <QGraphicsRectItem>
class MyRect: public QGraphicsRectItem{
public:
void keyPressEvent(QKeyEvent* event);
};
#endif // MYRECT_H
Bullet.cpp
#include "Bullet.h"
#include <QTimer>
Bullet::Bullet(){
setRect(0,0,10,50);
QTimer * timer = new QTimer();
connect(timer,SIGNAL(timeout()),this,SLOT(move()));
timer->start(50);
}
void Bullet::move(){
this->setPos(x(),y()-10);
}
main.cpp
#include <QApplication>
#include <QGraphicsScene>
#include "MyRect.h"
#include <QGraphicsView>
int main(int argc, char *argv[])
{
QApplication a(argc, argv);
QGraphicsScene * scene = new QGraphicsScene();
MyRect * rect = new MyRect();
rect->setRect(0,0,100,100);
rect->setFlag(QGraphicsItem::ItemIsFocusable);
rect->setFocus();
scene->addItem(rect);
QGraphicsView * view = new QGraphicsView(scene);
view->setHorizontalScrollBarPolicy(Qt::ScrollBarAlwaysOff);
view->setVerticalScrollBarPolicy(Qt::ScrollBarAlwaysOff);
view->show();
return a.exec();
}
MyRect.cpp
#include "MyRect.h"
#include<QKeyEvent>
#include <QGraphicsScene>
#include "Bullet.h"
#include<QDebug>
void MyRect::keyPressEvent(QKeyEvent *event)
{
if(event->key() == Qt::Key_Left)
{
setPos(x()-10,y());
}
else if(event->key() == Qt::Key_Right)
{
setPos(x()+10,y());
}
else if(event->key() == Qt::Key_Up)
{
setPos(x(),y()-10);
}
else if(event->key() == Qt::Key_Down)
{
setPos(x(), y()+10);
}
else if(event->key() == Qt::Key_Space)
{
Bullet * bullet = new Bullet();
bullet->setPos(x(), y());
scene()->addItem(bullet);
}
}
I have written some similar error i Qt, but still i can't resolve my.Thank you very much for your attention.

Answer 1

I got the same kind of error with this statement in a base class.
virtual void setInitiator(QPainter* painter, QImage* image);
Undefined reference to 'vtable for FractalObject'
FractalObject is my base class.
I derive classes which use the member function but there is no implementation in the base class. To fix things all I had to do is this:
virtual void setInitiator(QPainter* painter, QImage* image) = 0;
I'm guessing the assignment to zero forces a vtable to be created that holds a null pointer to the member function. This simple assignment fixed everything for me.