Serialize QGraphicsScene Binary Data By Using QDataStream

QGraphicsScene class enables easy management of QGraphicsItem instances in a 2D environment. QGraphicsScene acts as a container for custom QGraphicsItems.
Custom QDialog with a QGraphicsView helps to visualize QGraphicsItems that are included in a QGraphicsScene. By using addItem() function of QGraphicsScene, custom QGraphicsItems can be added to the QGraphicsScene instance. QGprahicsItem binary data such as x() and y() coordinates can be serialized to a QFile by using QDataStream.
Sample project started as a QT Gui Application and contains main.cpp, SceneToDataStream.h, SceneToDataStream.cpp, MyGraphicsItem.h and MyGraphicsItem.cpp files.
Project Directory Structure in Qt Creator IDE :

SceneToDataStream.pro is the project configuration file and contains:

QT       += core gui
TARGET = SceneToDataStream
TEMPLATE = app
SOURCES += main.cpp\
        SceneToDataStream.cpp \
    MyGraphicsItem.cpp
HEADERS  += SceneToDataStream.h \
    MyGraphicsItem.h

main.cpp file contains the custom QDialog instance and shows it.

#include <QApplication>
#include "SceneToDataStream.h"
int main(int argc, char *argv[])
{
    QApplication a(argc, argv);
    Dialog w;
    w.show();
    return a.exec();
}

SceneToDataStream.h file is the extended QDialog class header file.

#ifndef SCENETODATASTREAM_H
#define SCENETODATASTREAM_H
#include <QDialog>

class QGraphicsScene;
class MyGraphicsItem;
class QGraphicsView;
class QVBoxLayout;

class Dialog : public QDialog
{
    Q_OBJECT

public:
    Dialog(QWidget *parent = 0);
    ~Dialog();

public slots:
    void sl_saveSceneToFile();

private:
    QGraphicsScene* scene;
    MyGraphicsItem* item;
    QGraphicsView* view;
    QVBoxLayout* layout;
    QPushButton* btnSave;
};

#endif // SCENETODATASTREAM_H

SceneToDataStream.cpp file contains implementation details for extended QDialog class.

#include "SceneToDataStream.h"
#include "MyGraphicsItem.h"

#include <QGraphicsScene>
#include <QGraphicsView>
#include <QVBoxLayout>
#include <QPushButton>
#include <QFile>
#include <QList>
#include <QMessageBox>
#include <QDir>

Dialog::Dialog(QWidget *parent)
    : QDialog(parent)
{
    scene = new QGraphicsScene(this);
    item = new MyGraphicsItem();
    item->setPos(34,35);
    scene->addItem(item);
    view = new QGraphicsView(scene,this);
    layout = new QVBoxLayout(this);
    layout->addWidget(view);
    btnSave = new QPushButton("Save Scene To File");
    connect(btnSave, SIGNAL(clicked()), this, SLOT(sl_saveSceneToFile()));
    layout->addWidget(btnSave);
    setLayout(layout);
    resize(270,200);
}

Dialog::~Dialog()
{
    delete btnSave;
    delete layout;
    delete item;
    delete scene;
    delete view;
}

void Dialog::sl_saveSceneToFile()
{
    QString fileName = QDir::currentPath().append("/sceneData.txt");
    QFile file(fileName);
    if (!file.open(QIODevice::WriteOnly))
    {
            return;
    }
    QDataStream out(&file);
    QList<QGraphicsItem*> itemList = scene->items();
    int itemListSize = itemList.size();
    out << itemListSize;
    foreach( QGraphicsItem* item, itemList)
    {
        out << item->x();
        out << item->y();
    }
    QMessageBox::warning(this,"Success","Saved Scene Data to File");
    close();
}

sl_saveSceneToFile() slot of Dialog class is connected to QPushButton clicked signal and serializes number of all the items on the scene with item x() and y() coordinates respectively.

MyGraphicsItem is a derived custom QGraphicsItem class that implements boundingRect() and paint() functions of the parent. MyGraphicsItem is a rectangular derived QGraphicsItem and added to the QGraphicsScene.
MyGraphicsItem.h file contains custom QGraphicsItem class declaration.

#ifndef MYGRAPHICSITEM_H
#define MYGRAPHICSITEM_H
#include <QGraphicsItem>
class MyGraphicsItem : public QGraphicsItem
{
public:
    MyGraphicsItem(QGraphicsItem *parent = 0, QGraphicsScene *scene = 0);
    ~MyGraphicsItem();

protected:
    QRectF boundingRect() const;

    void paint(QPainter *painter, const QStyleOptionGraphicsItem *option,
               QWidget *widget);
};

#endif // MYGRAPHICSITEM_H

MyGraphicsItem.cpp file contains implementation details for custom QGraphicsItem class.

#include "MyGraphicsItem.h"
#include <QPainter>
MyGraphicsItem::MyGraphicsItem(QGraphicsItem* parent, QGraphicsScene* scene) : QGraphicsItem(parent,scene)
{
}

MyGraphicsItem::~MyGraphicsItem(){}

QRectF MyGraphicsItem::boundingRect() const
{
    qreal penWidth = 1;
    return QRectF(-10 - penWidth / 2, -10 - penWidth / 2,
                  20 + penWidth, 20 + penWidth);
}

void MyGraphicsItem::paint(QPainter *painter, const QStyleOptionGraphicsItem *option,
           QWidget *widget)
{
    Q_UNUSED(widget)
    Q_UNUSED(option)

    QPen pen;
    pen.setWidthF(2);
    pen.setStyle(Qt::DashLine);
    painter->setPen(pen);
    painter->setBrush(QBrush(QColor(50,120,80)));
    painter->drawRoundedRect(boundingRect(), 25, 25, Qt::RelativeSize);
}

sceneData.txt is the produced file that contains serialized binary data.