尝试解决办法

• QDialog::winEvent 拦截 if (message->message == WM_QUERYENDSESSION) 测试失败
• 重载 QApplication::commitData( QSessionManager & manager ) 会话管理  感谢QT官方回答者 http://qt-project.org/forums/viewthread/5223 测试成功

//QMyApplication.h
class QMyApplication: public QApplication
public:
           virtual void commitData ( QSessionManager & manager );
signals:
	void appShutdown();


//QMyApplication.cpp
void QMyApplication::commitData( QSessionManager & manager )
{
	//if (manager.allowsInteraction())
	{
		manager.release();
		emit appShutdown();
		//if (error) manager.cancel();
	}
}

//main.cpp
int main(int argc, char *argv[])
{
	QMyApplication a(argc, argv);
        a.exec();
}

//MainWindow.h
slots:
         void whenShutdownDothing();
//MainWindow.cpp

MainWindow()
{
        connect(qApp, SIGNAL(appShutdown()), this, SLOT(whenShutdownDothing()));
}

void MyApplication::commitData(QSessionManager& manager)
 {
     if (manager.allowsInteraction()) {
         int ret = QMessageBox::warning(
                     mainWindow,
                     tr("My Application"),
                     tr("Save changes to document?"),
                     QMessageBox::Save | QMessageBox::Discard | QMessageBox::Cancel);

         switch (ret) {
         case QMessageBox::Save:
             manager.release();
             if (!saveDocument())
                 manager.cancel();
             break;
         case QMessageBox::Discard:
             break;
         case QMessageBox::Cancel:
         default:
             manager.cancel();
         }
     } else {
         // we did not get permission to interact, then
         // do something reasonable instead
     }
 }