#include <QtGui>

class TChildWindow:public QMainWindow
{
public:
	TChildWindow(void);
	~TChildWindow(void);
private:
	void virtual mousePressEvent(QMouseEvent *event); 
};
//-------------------------------------------------------

#include "TChildWindow.h"

TChildWindow::TChildWindow(void)
{
	setStyleSheet("background-color: gray");	
}

TChildWindow::~TChildWindow(void)
{
}

void TChildWindow::mousePressEvent(QMouseEvent *event)
{
   this->close(); 
};

//----------------------------------------

#include <QtGui>
#include "TChildWindow.h"

class TMainWindow:public QMainWindow
{
Q_OBJECT
public:
	TMainWindow(void);
	~TMainWindow(void);
private:
    TChildWindow *childwindow;
	QWidget *mainWidget;
	QGridLayout *layout;
	QPushButton *button;
public slots:
    void slotPushButton(void);
};

//---------------------------

#include "TMainWindow.h"

TMainWindow::TMainWindow(void)
{

	mainWidget=new QWidget();
    layout=new QGridLayout();
	mainWidget->setLayout(layout);
	this->setCentralWidget(mainWidget);

	button=new QPushButton("OK");
	layout->addWidget(button);

	childwindow=new TChildWindow();
	connect(button,SIGNAL(clicked()),this,SLOT(slotPushButton()));
}

TMainWindow::~TMainWindow(void)
{
}

void TMainWindow::slotPushButton(void)
{
	childwindow->setParent(this);
	childwindow->setFixedWidth(this->width()/2);
	childwindow->setFixedHeight(this->height()/2);
	childwindow->move(20,20);
    childwindow->setWindowModality(Qt::WindowModal);	
	childwindow->show();
};

//---------------------------------------

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