[Qt]qmake and updating makefile

[ut`ler]

Hello,
I bought the book "Prentice Hall PTR: C++ GUI Programming with Qt 3". There's a chapter 2 (Subclassing dialogs) and there's the following text:

Visual C++'s output starts like this:

finddialog.obj : error LNK2001: unresolved external symbol
"public:~virtual bool __thiscall FindDialog::qt_property(int,
int,class QVariant *)"

If this ever happens to you, run qmake again to update the makefile, then rebuild the application.

I tried that few times but it doesn't working at all. My Visual Studio gives exatly such an error.
How I tried:
Start->Run->cmd - gone to the "qmake"-directory and typed in "qmake.exe -tp vc findDialog/dialog.pro", everything seems to be ok, but if I want rebuild in vstudio the same errors are caming again! What's wrong or was it my fault? Please help me to fix this problem
Here my SourceCode:

#include<qapplication.h>
#include<qcheckbox.h>
#include<qlabel.h>
#include<qlayout.h>
#include<qlineedit.h>
#include<qpushbutton.h>

#ifndef FINDDIALOG_H
#define FINDDIALOG_H
#include<qdialog.h>

class QCheckBox;
class QLabel;
class QLineEdit;
class QPushbutton;

class FindDialog : public QDialog
{
	Q_OBJECT
public:
	FindDialog(QWidget *parent = 0, const char *name = 0);
signals:
	void findNext(const QString &str, bool CaseSensitive);
	void findPrev(const QString &str, bool CaseSensitive);
private slots:
	void findClicked();
	void enableFindButton(const QString &text);
private:
	QLabel *label;
	QLineEdit *lineEdit;
	QCheckBox *caseCheckBox;
	QCheckBox *backwardCheckBox;
	QPushButton *findButton;
	QPushButton *closeButton;
};

#endif

FindDialog::FindDialog(QWidget *parent, const char *name) : QDialog(parent, name)
{
	setCaption(tr("Find"));

	label = new QLabel(tr("Find &what:"), this);
	lineEdit = new QLineEdit(this);
	label->setBuddy(lineEdit);

	caseCheckBox = new QCheckBox(tr("Match &case"), this);
	backwardCheckBox = new QCheckBox(tr("Search &backward"), this);

	findButton = new QPushButton(tr("&Find"), this);
	findButton->setDefault(true);
	findButton->setEnabled(false);

	closeButton = new QPushButton(tr("Close"), this);

	connect(lineEdit, SIGNAL(textChanged(const QString &)), this, SLOT(enableFindButton(const QString &)));
	connect(findButton, SIGNAL(clicked()), this, SLOT(findClicked()));
	connect(closeButton, SIGNAL(clicked()), this, SLOT(close()));

	QHBoxLayout *topLeftLayout = new QHBoxLayout;
	topLeftLayout->addWidget(label);
	topLeftLayout->addWidget(lineEdit);

	QVBoxLayout *leftLayout = new QVBoxLayout;
	leftLayout->addLayout(topLeftLayout);
	leftLayout->addWidget(caseCheckBox);
	leftLayout->addWidget(backwardCheckBox);

	QVBoxLayout *rightLayout = new QVBoxLayout;
	rightLayout->addWidget(findButton);
	rightLayout->addWidget(closeButton);
	rightLayout->addStretch(1);

	QHBoxLayout *mainLayout = new QHBoxLayout(this);
	mainLayout->setMargin(11);
	mainLayout->setSpacing(6);
	mainLayout->addLayout(leftLayout);
	mainLayout->addLayout(rightLayout);
}

void FindDialog::findClicked()
{
	QString text = lineEdit->text();
	bool caseSensitive = caseCheckBox->isOn();

	if(backwardCheckBox->isOn()) emit findPrev(text, caseSensitive);
	else emit findNext(text, CaseSensitive);
}

void FindDialog::enableFindButton(const QString &text)
{
	findButton->setEnabled(!text.isEmpty());
}

int main(int argc, char *argv[])
{
	QApplication app(argc, argv);
	FindDialog *dialog = new FindDialog;
	app.setMainWidget(dialog);
	dialog->show();
	return app.exec();
}