[Qt-interest] How can I pop-up a menu when I clikcked a button?

[Kermit Mei]

Hello,community!

I need to use a button to pop-up a menu. I can't use MenuBar, because it
can't show as a icon. So I set a button, and connect it to a slot
showMenu(): 

void MainWidget::showMenu() {
  QWidget *senderWidget = qobject_cast<QWidget *>(sender());
  if(senderWidget == 0)
    return;
  QMenu menu(this);
  foreach(QAction *act,confActions)
    menu.addAction(act);
  menu.exec(senderWidget->pos());
}

But, when I click the button, the menu always pop-up out of the current
Widget when I move the widget. I hope the menu can be inside the widget
which include the button. 

Thanks.
Kermit