托盘菜单出来了，无法响应，报错：Object::connect: No such slot QSystemTrayIcon::helpAction() 。
#include <QApplication>
#include <QSystemTrayIcon>
#include <QMenu>
#include <QAction>
void helpAction(){
qDebug("helpAction");
}
int main(int argc, char *argv[])
{
QApplication a(argc, argv);
qDebug("begin");
QWidget *window=new QWidget;
window->show();
QSystemTrayIcon *systray=new QSystemTrayIcon();
systray->setToolTip("I am tray!");
systray->setIcon(QIcon(":icon.png"));
systray->setVisible(true);
QAction *aboutAction=new QAction("about",systray);
QMenu *traymenu=new QMenu();
traymenu->addAction(aboutAction);
systray->setContextMenu(traymenu);
QObject::connect(aboutAction, SIGNAL(triggered()), systray, SLOT(helpAction()));
return a.exec();
}
| 
