qt - QGraphicsItem validating a position change -

i have custom qgraphicsitem implementation. need able limit item can moved - i,e. restrict area. when checked qt documentation suggested:

qvariant component::itemchange(graphicsitemchange change, const qvariant &value)  {      if (change == itempositionchange && scene()) {          // value new position.          qpointf newpos = value.topointf();          qrectf rect = scene()->scenerect();          if (!rect.contains(newpos)) {              // keep item inside scene rect.              newpos.setx(qmin(rect.right(), qmax(newpos.x(), rect.left())));              newpos.sety(qmin(rect.bottom(), qmax(newpos.y(), rect.top())));              return newpos;          }      }      return qgraphicsitem::itemchange(change, value);  } 

so basically, check position passed itemchange, , if don't it, change , return new value.

seems simple enough, except doesn't work. when checked call stack see itemchange being called qgraphicsitem::setpos, doesn't @ return value. there no purpose me returning changed position, no 1 looking @ it. see code qgraphicsitem.cpp

// notify item position changing.     const qvariant newposvariant(itemchange(itempositionchange, qvariantfromvalue<qpointf>(pos)));     qpointf newpos = newposvariant.topointf();     if (newpos == d_ptr->pos)         return;      // update , repositition.     d_ptr->setposhelper(newpos);      // send post-notification.     itemchange(qgraphicsitem::itempositionhaschanged, newposvariant);     d_ptr->sendsceneposchange(); 

any suggestions? hoping avoid re-implementing whole click , drag behavior myself using mouse-down mouse-move etc..., suppose have if can't find better idea.

i didn't try looks me checking return position. returned restricted position used in constructor of newposvariant converted newpos. it's used set position of item if it's different current one.