#include <QtWidgets>
#include <QMainWindow>
#include <QtGui>
#include <Windows.h>

class TChild : public QWidget
{
public:
	TChild(QWidget* parent, QWidget* window2)
		:
		QWidget(parent, Qt::Dialog),
		m_button(parent),
		m_window2(window2)
		{
		}
		void mouseReleaseEvent(QMouseEvent*)
		{
			m_button->setParent(m_window2, m_button->windowFlags());
			//SetWindowLongPtr((HWND)winId(), GWL_HWNDPARENT, m_window2 ? (LONG_PTR)m_window2->winId() : 0);
			m_button->show();
		}
	QWidget*	m_button;
	QWidget*	m_window2;
};
 
int main(int argc, char** argv)
{
	QApplication app(argc, argv);

	QWidget* window1 = new QWidget(0, Qt::Window);
	QPushButton* button = new QPushButton(QLatin1String("Button"), window1);
	window1->setWindowTitle(QLatin1String("Window 1"));
	window1->resize(400,400);
	window1->move(100,100);
	window1->show();

	QWidget* window2 = new QWidget(0, Qt::Window);
	window2->setWindowTitle(QLatin1String("Window 2"));
	window2->resize(400,400);
	window2->move(300,300);
	window2->show();

	TChild* child = new TChild(button, window2);
	child->setWindowTitle(QLatin1String("Child of button"));
	child->resize(200,200);
	child->move(500,500);
	child->show();

	return app.exec();
}