Qt QGraphicsScene is not accessable from QGraphicsView (on Qt 5.6.1) -


i new qt. trying catch mouse press , release in qgraphicsview area , draw line. this, extended qgraphicsview , called myqgraphicsview. seems scene not attached since added "hello world" , never appears in view. here code extended class:

class myqgraphicsview : public qgraphicsview {   q_object  public:  myqgraphicsview(qgraphicsscene *scene, qwidget *parent = q_nullptr) : qgraphicsview(scene,parent){      //  qgraphicsview::qgraphicsview(scene,parent); }    qpoint *pointptr, *startpos,*endpos;  qgraphicsview *cv;//maa  qgraphicsscene *c;  qgraphicsscene *sceneptr; // maa protected: void paintevent(qpaintevent *event) {        show();  }  void mousepressevent(qmouseevent *event) {     // pos wrt widget. global wer global screen     qdebug()<<" mouse pressed @ "<<qwidget::mapfromglobal(event->globalpos()); //globalx();     startpos = new qpoint;     startpos->setx(qwidget::mapfromglobal(event->globalpos()).x());     startpos->sety(qwidget::mapfromglobal(event->globalpos()).y());  }  void mousereleaseevent(qmouseevent *event) {    qdebug()<<" mouse relase pressed @ x="<<event->globalpos().x()<<" y ="<<event->globalpos().y();    endpos = new qpoint;    endpos->setx(qwidget::mapfromglobal(event->globalpos()).x());    endpos->sety(qwidget::mapfromglobal(event->globalpos()).y());    c->addline(0,0,50,50);    update(); }  void mousemoveevent ( qmouseevent * event ) {   //show x , y coordinate values of mouse cursor here   qdebug()<<"x:"<<qstring::number(event->x())<<"-- y:"<<qstring::number(event->y());   endpos = new qpoint;  }   }

it seems mouse gets detected , right methods called. however, neither "hello world" nor line gets drawn in view. tried cv1->setscene on view , did not either.

so declared 2nd view pointer called cv2 , using qgraphicsview. information seems work fine there , gets drown. read through posting , seems suggestion of setting event filters added both views (cv1 , cv2). event filter returns false events ( should default behavior documentation). did not anything. here code snippet in great.cpp cv1 , cv2. notice in cv1 (mymyqgraphicsview instance), created pointer scene (called c) , gets assigned c1 can addline it. 

        c1 = new qgraphicsscene(0,0,500,300,this);       text= c1->addtext("hello, world!");      text->setflag(qgraphicsitem::itemismovable);     text->setvisible(true);     cv1 = new myqgraphicsview(c1,this);     cv2= new qgraphicsview(c1,this);     keypresseater *keypresseaterptr = new keypresseater(this);     cv1->installeventfilter(keypresseaterptr);     cv2->installeventfilter(keypresseaterptr);     cv1->c =c1;      layout = new qgridlayout;     layout->addwidget(toplabel,0,0);     layout->addwidget(wellcoord,1,0);     layout->addwidget(cv1,1,1,1,-1); <-view added great class     layout->addwidget(timestepgroup,2,0);     setlayout(layout);

finally, here great.h:

 myqgraphicsview *cv1;//maa  qgraphicsview *cv2;//maa   qgraphicsscene *c1; // maa   public:  void paintevent(qpaintevent *event) {     // maa      cv2->show();   }   protected:    void mousepressevent(qmouseevent *event) {      qdebug()<<"gridwell mouse pressed @ "<<qwidget::mapfromglobal(event->globalpos()); //globalx();     startpos = new qpoint;     startpos->setx(qwidget::mapfromglobal(event->globalpos()).x());     startpos->sety(qwidget::mapfromglobal(event->globalpos()).y());     qwidget::mousepressevent(event);  } void mousereleaseevent(qmouseevent *event) {      qdebug()<<"gridwell mouse released @ x="<<event->globalpos().x()<<" y ="<<event->globalpos().y();    qwidget::mousereleaseevent(event);     endpos = new qpoint;    endpos->setx(qwidget::mapfromglobal(event->globalpos()).x());    endpos->sety(qwidget::mapfromglobal(event->globalpos()).y());     lineitemptr = c1->addline(startpos->x(),startpos->y(),(endpos->x())- (startpos->x()),(endpos->y())-(startpos->y()) );    lineitemptr->setvisible(true);    cv2->update(); }  void mousemoveevent ( qmouseevent * event ) {   //show x , y coordinate values of mouse cursor here   qdebug()<<"gridwell x:"<<qstring::number(event->x())<<"-- y:"<<qstring::number(event->y());   endpos = new qpoint;  }

finally, here keyeater cut , pasted documentation:

class keypresseater : public qobject {   q_object  public:   keypresseater(qobject *parent = q_nullptr) : qobject (parent){   }  protected:    bool eventfilter(qobject *obj, qevent *event)   {      return(false); // propagates events   } };

any ideas why cv1 not scene c1 ( since not print "hello world". cv2 does?

thanks help!

update: did more investigation , changed following routine:

 void mygraphicsview::mousereleaseevent(qmouseevent *event) {    qdebug()<<" mouse relase pressed @ x="<<event->x()<<" y ="<<event->y();    endpos = new qpoint;    endpos->setx(event->x());    endpos->sety(event->y());         c->addline(0,0,event->x(),50);    }

now, when click inside cv1 view area, see line in cv2 since both cv2 , cv1 views pointing same scene (cv1->c = c1; line in great.cpp). proves scene not mapped correctly in cv2 since not "hello world" shows up. baffled since seems simple object being passed constructor shown in many examples.


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