how to use scene object of main file in other file?

Question

I tried to make tictactoe game using Qt and Qgraphicsview but when I draw x on board using Graphicstextitem in mousePressEvent , X does not appear. how fix that ?

I think the problem is that scene of textitem Different from scene of main file but I do not know how fix that.

main.cpp:

int main(int argc, char *argv[])
 {
   QApplication a(argc, argv);
      Game *gm = new Game;

     Game *rect1=new Game;
  gm->scenc->setSceneRect(0,0,800,600);
  rect1->setRect(160,100,150,150);
  gm->scenc->addItem(rect1);
  gm->view->setScene(gm->scenc);
  gm->view->show();
  return a.exec();
 }

in game.cpp:

#include <game.h>

 Game::Game()
 {
  scenc= new QGraphicsScene;
  view = new QGraphicsView;
  text= new QGraphicsTextItem;
}

 void Game::mousePressEvent(QGraphicsSceneMouseEvent *event)
 {
    if (event->buttons() == Qt::LeftButton )
     { 
                 text->setPlainText("X");
                 text->setFont(QFont("Tahoma",24));
                 text->setPos((160+160+120)/2,140);
                 scenc->addItem(text);


     } 

   }

in game.h :

 class Game : public QObject , public QGraphicsRectItem
{
    Q_OBJECT
    public:

     Game();

     QGraphicsScene *scenc;
     QGraphicsView *view;
     QGraphicsTextItem *text;
     void mousePressEvent(QGraphicsSceneMouseEvent *event);




       };

Answer 1

The following example illustrates how to do it the right way. Firstly, you have to notice, that Game::mousePressEvent doesn't override any virtual function. It's a good habit to use the override keyword and to drop the virtual keyword in order to be sure, that a virtual function is overwritten.

Game is not derived from QGraphicsScene and has therefore no mousePressEvent member.

Try the following example app.

MyScene.h

#pragma once
#include <QWidget>
#include <QDebug>
#include <QHBoxLayout>
#include <QGraphicsScene>
#include <QGraphicsView>
#include <QGraphicsTextItem>
#include <QGraphicsSceneMouseEvent>

class MyScene : public QGraphicsScene {
    Q_OBJECT
public:
    MyScene(QWidget* parent = nullptr) : QGraphicsScene(parent) {
        setSceneRect(0, 0, 800, 600);       
    }
    void mouseDoubleClickEvent(QGraphicsSceneMouseEvent* mouseEvent) override {
        if (mouseEvent->buttons() == Qt::LeftButton)
        {
            auto text = new QGraphicsTextItem;
            addItem(text);
            text->setPlainText("X");
            text->setPos(mouseEvent->scenePos());
        }
    }
private:
    QGraphicsView* mView;
    QGraphicsTextItem* mText;
};

main.cpp

#include <QApplication>
#include <QGraphicsScene>
#include <QGraphicsView>
#include <QGraphicsTextItem>
#include "MyScene.h"

int main(int argc, char* argv[])
{
    QApplication a(argc, argv);
    auto scene = new MyScene;
    auto view = new QGraphicsView;
    view->setScene(scene);
    view->show();
    return a.exec();
}