int xx = 0;
int yy = 0;

void QtTest::paintEvent(QPaintEvent*event)
{
    QPainter painter(this);
    painter.setPen(QPen(Qt::black,1));
    painter.drawRect(50+xx,50+yy,50,50);
}

void QtTest::keyPressEvent(QKeyEvent*event)
{
    switch(event->key())
    {
        case Qt::Key_A:
            xx--;break;
        case Qt::Key_D:
            xx++;break;
        case Qt::Key_W:
            yy--;break;
        case Qt::Key_S:
            yy++;break; 
    }

    repaint ();

    QWidget::keyPressEvent(event);
}