qt - QGraphicsView rubber band selection rectangle not visible -

i have qgraphicsview widget lots of items on scene. panning view on ctr+left mouse click , zooming rectangle of rubber band created left mouse button drag. not able see rubber band selection rectangle (dotted lines) whereas rubberband selection functionality works fine. can me understand this?.
i use these flags in view:

settransformationanchor(qgraphicsview::anchorundermouse); setviewportupdatemode(qgraphicsview::smartviewportupdate); setrenderhints(qpainter::highqualityantialiasing | qpainter::smoothpixmaptransform); setoptimizationflag(qgraphicsview::dontsavepainterstate,true); setcachemode(qgraphicsview::cachebackground); setoptimizationflag(qgraphicsview::dontadjustforantialiasing); setviewport(new qglwidget); 

below event handlers.

mouse press event handler:

void myview::mousepressevent(qmouseevent* event) {     if(event->button()==qt::leftbutton)     {                if(event->modifiers()==qt::controlmodifier)         {             setdragmode(qgraphicsview::nodrag);             m_rubberbandactive = false;                      mousepressed=true;             m_lastdragpos = event->pos();             return;         }         else         {                        setdragmode(qgraphicsview::rubberbanddrag);             m_rubberbandorigin = event->pos();             m_rubberbandactive = true;         }     }        event->accept();    }    else    {           qwidget::mousepressevent(event);    }     } 

mouse move event:

void myview::mousemoveevent(qmouseevent* event) { if(mousepressed) {     qpointf delta = maptoscene(event->pos()) - maptoscene(m_lastdragpos);     this->panview(delta);     m_lastdragpos = event->pos();        return; } event->accept(); } 

mouse release event handler:

void myview::mousereleaseevent(qmouseevent *event) { if (m_rubberbandactive) {     qpoint rubberbandend = event->pos();             qrectf zoomrectinscene = qrectf(maptoscene(m_rubberbandorigin),maptoscene(rubberbandend));      fitinview(zoomrectinscene, qt::keepaspectratio);     m_rubberbandactive = false; }  mousepressed=false; event->accept(); } 

pan view:

void myview::panview(qpointf delta) {     qpoint viewcenter(viewport()->width() / 2 + delta.x(), viewport()->height() / 2 + delta.y());     qpointf newcenter = maptoscene(viewcenter);     centeron(newcenter); }