неопределенная ссылка на класс

Я строю небольшую игру в Qt4. вот код:

lcdcontrol.h:

#ifndef LCDCONTROL_H
#define LCDCONTROL_H#include <QLCDNumber>
#include <QtGui>
#include <QWidget>

class lcdControl: public QWidget
{
Q_OBJECT

public:
lcdControl(QWidget *parent=0);

signals:
void valueChanged(int newValue);

public slots:
void setValue(int value);
//void setRange(int minValue, int maxValue);
//void quit();

private:
QSlider *slider;
//QPushButton *quitbutton;

};#endif

lcdcontrol.cpp:

#include <QLCDNumber>
#include <QSlider>
#include <QGridLayout>

#include "lcdcontrol.h"
lcdControl::lcdControl(QWidget *parent): QWidget(parent)
{

QLCDNumber *lcd = new QLCDNumber(2);                //2 for 2 digits
lcd->setSegmentStyle(QLCDNumber::Filled);

slider = new QSlider(Qt::Horizontal);
slider->setRange(0,99);
slider->setValue(0);

connect(slider,SIGNAL(valueChanged(int)),lcd,SLOT(display(int)));
connect(slider,SIGNAL(valueChanged(int)),this,SIGNAL(valueChanged(int)));

QVBoxLayout *layout = new QVBoxLayout;
layout->addWidget(lcd);
layout->addWidget(slider);
setLayout(layout);

setFocusProxy(slider);
}

void lcdControl::setValue(int value)
{
slider->setValue(value);
}

Drawing.h:

#ifndef DRAWING_H
#define DRAWING_H

#include <QPushButton>

class drawingClass : public QWidget
{
Q_OBJECT
public:
drawingClass(QWidget *parent=0);

private:
QPushButton *quitbutton;
};#endif

Drawing.cpp:

#include <QVBoxLayout>
#include <QGridLayout>
#include <QtGui>
#include "drawing.h"#include "lcdcontrol.h"
drawingClass::drawingClass(QWidget *parent): QWidget(parent)
{

quitbutton = new QPushButton(tr("&Quit!"));
connect(quitbutton,SIGNAL(clicked()),qApp,SLOT(quit()));

lcdControl *angle = new lcdControl;
lcdControl *force = new lcdControl;

QVBoxLayout *leftlayout = new QVBoxLayout;
leftlayout->addWidget(angle);
leftlayout->addWidget(force);

QGridLayout *mainlayout = new QGridLayout;
mainlayout->addWidget(quitbutton,0,0);
mainlayout->addLayout(leftlayout);
mainlayout->setColumnStrech(1,10);
setLayout(mainlayout);
}

main.cpp

#include <QApplication>
#include <QtGui>
#include "drawing.h"
int main(int argc, char **argv)
{
QApplication app(argc,argv);
drawingClass ob;
ob.resize(500,200);
ob.show();
return app.exec();
}

Ошибка:

main.cpp:(.text.startup+0x28): undefined reference to `drawingClass::drawingClass(QWidget*)'
main.cpp:(.text.startup+0x6e): undefined reference to `vtable for drawingClass'
main.cpp:(.text.startup+0x77): undefined reference to `vtable for drawingClass'
main.cpp:(.text.startup+0xb4): undefined reference to `vtable for drawingClass'
main.cpp:(.text.startup+0xbd): undefined reference to `vtable for drawingClass'
collect2: ld returned 1 exit status

Пожалуйста, помогите мне с этим.