QGraphicsItem

~~~~~~~~~~
mainwindow.cpp
~~~~~~~~~~
#include "mainwindow.h"
#include <QDebug>

MainWindow::MainWindow()
{
  scene = new QGraphicsScene;
  view = new QGraphicsView;
  view->setScene(scene);
  button = new QPushButton("Item");
  QGridLayout  *layout = new QGridLayout;
  layout->addWidget(button);
  layout->addWidget(view);
  setLayout(layout);
  connect(button, SIGNAL(clicked()), this, SLOT(createItem()));
}

void MainWindow::createItem()
{
  myEntity = new Item;
  scene->addItem(myEntity);
  count_items();
}

void MainWindow::count_items()
{
    qDebug() << scene->items().count();
    qDebug() << scene->items();
}

MainWindow::~MainWindow()
{
}

~~~~~~~~~~
item.cpp
~~~~~~~~~~
#include "item.h"

Item::Item()
{
  ClickFlag = true;
  PaintFlag = false;
}

Item::~Item()
{
}

QRectF Item::boundingRect() const
{
   // outer most edges
   return QRectF(0,0,1450,1400);
}
void Item::mousePressEvent(QGraphicsSceneMouseEvent *event)
{
  if(event->button()==Qt::LeftButton){
    if(ClickFlag){
        x = event->pos().x();
        y = event->pos().y();
        PaintFlag = true;
        ClickFlag = false;
    }
  }
}

void Item::paint(QPainter *painter, const QStyleOptionGraphicsItem *option,
                  QWidget *widget)
{
  if(PaintFlag){
    QPen paintPen;
    paintPen.setWidth(4);
    pt.setX(x);
    pt.setY(y);
    painter->setPen(paintPen);
    painter->drawPoint(x,y);
    update();
  }
}