#include <QApplication>
#include <QMainWindow>
#include <QMouseEvent>
#include <QDialog>

class Dialog : public QDialog
{
public:

    Dialog(QWidget *parent = 0)
        : QDialog(parent)
    {
        setMinimumSize(150,150);

        pDialog = new QDialog(this);
        pDialog->setVisible(false);
    }

    void mousePressEvent(QMouseEvent* event)
    {
        Q_UNUSED(event);
        pDialog->show();
    }

    QDialog* pDialog;

};

class MainWindow : public QMainWindow
{
public:
    MainWindow(QWidget *parent = 0)
        : QMainWindow(parent)
    {
        setMinimumSize(300,300);

        pChildDialog = new Dialog(this);
        pChildDialog->show();
    }

    ~MainWindow()
    {

    }

    QDialog* pChildDialog;
};



int main(int argc, char *argv[])
{
    QApplication a(argc, argv);
    MainWindow w;
    w.show();

    return a.exec();
}