宣告

class CLineItem : public QObject,public QGraphicsItem
{
    Q_OBJECT
    Q_INTERFACES(QGraphicsItem)
public:
    explicit CLineItem(QObject *parent = 0);
    ~CLineItem(void);

    virtual QRectF boundingRect() const;
    virtual void paint(QPainter *painter, const QStyleOptionGraphicsItem *option, QWidget *widget);

    void
 
 setLineItem(QPointF startP, QPointF endP);
    void setColor(QColor color);

private:
    void CreatePointNodes(void);

private:
    QPointF         m_EndP;
    QPointF         m_points[3];
    QColor          m_Color;
};

定義：

CLineItem::CLineItem(QObject *parent) : QObject(parent)
{
    //setFlag(ItemIsMovable);
 

    setFlag(ItemIsSelectable);
    setAcceptHoverEvents(true);

    m_Color = TypeLineColor;
}

CLineItem::~CLineItem(void)
{

}

QRectF CLineItem::boundingRect() const
{
    return QRectF(0, 0, m_EndP.x(), m_EndP.y());
}

void CLineItem::paint(QPainter *painter, const QStyleOptionGraphicsItem *option, QWidget *widget)
{
    painter->setRenderHint(QPainter::Antialiasing, true
 
);                   //設定反走樣，防鋸齒
    QPen pen(m_Color, 2, Qt::SolidLine, Qt::RoundCap, Qt::RoundJoin);
    QBrush brush(m_Color, Qt::SolidPattern);

    painter->setPen(pen);
    painter->setBrush(brush);

    QLineF line(0, 0, m_EndP.x(), m_EndP.y());
    painter->drawLine(line);

    painter->drawPolygon(m_points, 3);

    /*pen.setWidth(1);
    painter->setPen(pen);
    brush.setColor(QColor(0,0,0,0));
    painter->setBrush(brush);
    painter->drawRect(boundingRect());*/
}

void CLineItem::setLineItem(QPointF startP, QPointF endP)
{
    m_EndP = endP - startP;

    CreatePointNodes();
}

void CLineItem::setColor(QColor color)
{
    m_Color = color;
}

void CLineItem::CreatePointNodes(void)
{
    float angle = atan2(m_EndP.y(), m_EndP.x()) + 3.1415926;//

    m_points[0] = m_EndP;
    m_points[1].setX(m_EndP.x() + ExtRefArrowLenght * cos(angle - ExtRefArrowDegrees));//求得箭頭點1座標
    m_points[1].setY(m_EndP.y() + ExtRefArrowLenght * sin(angle - ExtRefArrowDegrees));
    m_points[2].setX(m_EndP.x() + ExtRefArrowLenght * cos(angle + ExtRefArrowDegrees));//求得箭頭點2座標
    m_points[2].setY(m_EndP.y() + ExtRefArrowLenght * sin(angle + ExtRefArrowDegrees));
}

使用：

CLineItem *LineItem = new CLineItem(this);
LineItem->setLineItem(startP, endP);
LineItem->setPos(startP);
m_Scene->addItem(LineItem);

圖中為用此自定義類建立的三個物件：