How to color arc in Qt?

tushu

I have a QGraphicsItem which is made of Line, Arc's and Circle. I have drawn a digital gate XNOR using arcs and lines and circles and colored it with blue color.
So when I initially load it looks like this:

But when I click somewhere else, arc's color gets disappeared. And it looks like this:

I have colored it like this:

class myPoly: public QGraphicsPathItem 
{
   public:
    explicit myPoly();
    myPoly(QPainterPath p) : QGraphicsPathItem(p) {}
}         

   //Drawing Arc
    for (unsigned int i = 0; i < iter->second._allArcs.size(); i++) 
     {       
        // getting 6 co-ordinates for Arc
        
        QPointF from(first, second);
        QPointF to(third, fourth);
        QPointF center(fifth, sixth);
        
        QLineF lineFrom{center, from};
        QLineF lineTo{center, to};
        qreal radius = lineFrom.length();
        QRectF bounding{center - QPointF{radius, radius},
                        center + QPointF{radius, radius}};
        
        QRectF bounding1(bounding.x() + x, bounding.y() + y, bounding.width(),bounding.height());
        
  // Use QLineF to calculate angles wrt horizontal axis.
        qreal startAngle = lineFrom.angle();
        qreal sweep = lineFrom.angleTo(lineTo);
        
        QPainterPath path;
        path.moveTo(from.x(), from.y());
        
        path.arcTo(bounding1, startAngle, sweep);
        myPoly* poly = new myPoly(path);
        
        poly->createArc();
        scene->addItem(static_cast<QGraphicsPathItem*>(poly));
  }   
            

 class myLine: public QGraphicsLineItem
{
  public:
    myLine();
    myLine(int x1,int y1,int x2 ,int y2,QGraphicsItem *parent = nullptr)
        : QGraphicsLineItem(x1,y1,x2,y2,parent)
    {}
    void DrawLine();
};         

// Drawing line 
for (unsigned int i = 0; i < iter->second._allLines.size(); i++) 
{
  // getting 4 co-ordinates of lines.
  myLine* line = new myLine(first,second,third,fourth);
  line->DrawLine();
  scene->addItem(static_cast<QGraphicsLineItem*>(line));
 }
  
void myLine::DrawLine()
{
    this->setPen(QPen(QColor("blue"), 1));
}

void myPoly::createArc()
{
   QPen mPen;
   mPen.setWidth(1);
   mPen.setBrush(Qt::blue);
   this->setPen(mPen);
}

Why this is happening ? And how to avoid it ?