QGraphicsScene

#ifndef INFOITEM_H
#define INFOITEM_H

#include <QGraphicsObject>
#include <QPainter>

class InfoItem : public QGraphicsObject
{
    Q_OBJECT
public:
    explicit InfoItem(QString title, QGraphicsItem *parent = nullptr);
    QRectF boundingRect() const;
    void paint(QPainter *painter, const QStyleOptionGraphicsItem *option, QWidget *widget);

protected:
    virtual void mouseDoubleClickEvent(QGraphicsSceneMouseEvent *event) override;

signals:
    void doubleClicked(const QString& title);

private:
    QString m_title;
};

#endif // INFOITEM_H

#include "infoitem.h"

InfoItem::InfoItem(QString title, QGraphicsItem *parent)
    : QGraphicsObject(parent),
      m_title(title)
{

}

QRectF InfoItem::boundingRect() const
{
    return QRectF (-20, -20, 40, 40);
}

void InfoItem::paint(QPainter *painter, const QStyleOptionGraphicsItem *option, QWidget *widget)
{
    painter->setPen(Qt::black);
    painter->setBrush(Qt::green);
    painter->drawRect(-20, -20, 40, 40);
    Q_UNUSED(option);
    Q_UNUSED(widget);
}

void InfoItem::mouseDoubleClickEvent(QGraphicsSceneMouseEvent *event)
{
    emit doubleClicked(m_title);
    QGraphicsObject::mouseDoubleClickEvent(event);
}

#ifndef WIDGET_H
#define WIDGET_H

#include <QWidget>
#include <QGraphicsScene>

namespace Ui {
class Widget;
}

class Widget : public QWidget
{
    Q_OBJECT

public:
    explicit Widget(QWidget *parent = 0);
    ~Widget();

private:
    Ui::Widget *ui;
    QGraphicsScene *m_scene;
};

#endif // WIDGET_H

#include "widget.h"
#include "ui_widget.h"

#include "infoitem.h"

/* Функция для получения рандомного числа
 * в диапазоне от минимального до максимального
 * */
static int randomBetween(int low, int high)
{
    return (qrand() % ((high + 1) - low) + low);
}

Widget::Widget(QWidget *parent) :
    QWidget(parent),
    ui(new Ui::Widget)
{
    ui->setupUi(this);
    this->resize(640,640);
    this->setFixedSize(640,640);

    m_scene = new QGraphicsScene(this);
    ui->graphicsView->resize(600,600);
    ui->graphicsView->setScene(m_scene);

    for (int i = 0; i < 10; ++i)
    {
        InfoItem* item = new InfoItem("Info Item number - " + QString::number(i));
        item->setPos(randomBetween(50, 550), randomBetween(50, 550));
        m_scene->addItem(item);

        connect(item, &InfoItem::doubleClicked, [this](const QString& str){
            ui->label->setText(str);
        });
    }
}

Widget::~Widget()
{
    delete ui;
}