直接代碼：

    QPainter *painter;
    static const double Pi = 3.14159265358979323846264338327950288419717;

    static double TwoPi = 2.0 * Pi;

    QLineF line(sourcePoint,destPoint);

    if (qFuzzyCompare(line.length(), qreal(0.)))

        return;

    painter->setPen(QPen(Qt::black, 1, Qt::SolidLine, Qt::RoundCap, Qt::RoundJoin));

    painter->drawLine(line);

    double angle = ::acos(line.dx() / line.length());

    if (line.dy() >= 0)

        angle = TwoPi - angle;

    QPointF destArrowP1 = destPoint + QPointF(sin(angle - Pi / 3) * arrowSize,

                                              cos(angle - Pi / 3) * arrowSize);

    QPointF destArrowP2 = destPoint + QPointF(sin(angle - Pi + Pi / 3) * arrowSize,

                                              cos(angle - Pi + Pi / 3) * arrowSize);

    painter->drawLine(QLineF(destArrowP1,destPoint));

    painter->drawLine(QLineF(destArrowP2,destPoint));

http://blog.csdn.net/u010177010/article/details/51496188

Qt的paint函數重寫，以及QPaint給一條線繪制箭頭