SIGSEGV when using inherited QGraphicsScene

Question

I'm trying to inherit from a QGraphicsScene but somehow that crashes my program when I try to use it. I guess somewhere I'm missing a small thing, but I couldn't figure it out. Here is a minimal example of what I tried so far:

myscene.h

#ifndef MYSCENE_H
#define MYSCENE_H

#include <QGraphicsScene>

class MyScene : public QGraphicsScene
{
    Q_OBJECT

    QPen* pen_bg;

public:
    explicit MyScene(QObject* parent=nullptr);
    ~MyScene();
};

#endif // MYSCENE_H

myscene.cpp

#include "myscene.h"

MyScene::MyScene(QObject* parent):
    QGraphicsScene (parent)
{
    pen_bg = new QPen(Qt::blue);
}

MyScene::~MyScene()
{
    delete pen_bg;
}

mainwindow.cpp

#include "mainwindow.h"
#include "ui_mainwindow.h"
#include "myscene.h"

MainWindow::MainWindow(QWidget *parent) :
    QMainWindow(parent),
    ui(new Ui::MainWindow)
{    
    MyScene *m_scene = new MyScene(this);
    ui->graphicView->setScene(m_scene);
}

As soon as I call the setScene(m_scene) function, the program crashes with a SIGSEGV.

Answer 1

If you use the UI file, you need to first call setupUi() before using it, otherwise the UI elements are not initialized. See docs: http://doc.qt.io/qt-5/designer-using-a-ui-file.html

Add

 ui->setupUi(this); 

to your MainWindow constructor.