bool aboutTest::event(QEvent *mEvent)
{   
    if(mEvent->type() == QEvent::EnterWhatsThisMode)    //не даем войти в режим WhatsThis
        QWhatsThis::leaveWhatsThisMode();
    else if (mEvent->type()==QEvent::QueryWhatsThis)    //при нажатии на "?" показываем окно "О программе"
    {
        about();
    }
    return QMainWindow::event(mEvent);
}

void aboutTest::about()
{
    QMessageBox::about(this, tr("About Icons"),
            tr("The <b>Icons</b> example illustrates how Qt renders an icon in "
               "different modes (active, normal, disabled, and selected) and "
               "states (on and off) based on a set of images."));
}

//QComboBox *linestyleBox;

linestyleBox->setIconSize(QSize(40, 10));
QPen pen;
QPainter paint;
pen.setWidth(3);
pen.setColor(QColor(Qt::black));
paint.begin(&pixmap);

//Solid
pixmap.fill(QColor(Qt::white));
pen.setStyle(Qt::SolidLine);
paint.setPen(pen);
paint.drawLine(0, 5, 40, 5);
linestyleBox->insertItem(0, QIcon(pixmap), "Solid line", Qt::SolidLine);
//DashLine
pixmap.fill(QColor(Qt::white));
pen.setStyle(Qt::DashLine);
paint.setPen(pen);
paint.drawLine(0, 5, 40, 5);
linestyleBox->insertItem(0, QIcon(pixmap), "Dash line", Qt::DashLine);
//... другие типы линий