QGraphicsView Scale / Zoom Issue & QGraphicsRectItem paint failed to called

[SandyMedical]

My work Environment :Qt 5.8 MSVC2015 64bit, QT GraphicsView, QGraphicsRectItem, Windows 7 64 bit.

Issues : When I zoom in & zoom out on GraphicsView, I call GraphicsView scale method. But When I add QGraphicsRectItem to scene it failed to call its paint method.

my class hierarchy :

class GraphicsView : public QGraphicsView
class mySquare : public QObject, public QGraphicsRectItem
class Scene : public QGraphicsScene

Code :

//////*****Draw Rect in QGraphicsRectItem *****////////////

void mySquare::paint(QPainter *painter, const QStyleOptionGraphicsItem *option, QWidget *widget)
{
      QRectF rect(0,0,_width,_height);
      painter->drawRect(rect);
}

void GraphicsView::wheelEvent(QWheelEvent * event)
{
  int angle = event->angleDelta().y(); // angle will tell you zoom in or out.
  double scaleFactor = 1.15; //How fast we zoom
  setTransformationAnchor(QGraphicsView::AnchorUnderMouse);
  if (angle > 0)
  {
      qDebug()<<"Zoom in";
      scale(scaleFactor, scaleFactor);
  }
  else
  {
      qDebug()<<"Zoom out";
      scale(1.0 / scaleFactor, 1.0 / scaleFactor);
  }
      mySquare  _square = new mySquare(0,blankImage);
     _square->setPos(QPointF(0, 0));
//Bug!!! Why after scale function call, _square failed to draw rect in paint method.
      _scene->addItem(_square);        //add square to scene. 
      _square->update(); 
}

my git code
I spend days & hours but still not able to find out why it QGraphicsRectItem failed to print, when scale method get called. Any suggestion is highly appreciated ?