Error in setting in event filter : Can not cast to its private base class QObject

Question

I am trying to set event filter for rubber band rectangle zoom in. But getting the following error

widget.cpp:29:42: error: cannot cast 'SchematicDesign' to its private base class 'QObject' schematicdesign.h:13:68: note: constrained by implicitly private inheritance here

widget.h

QT_BEGIN_NAMESPACE
namespace Ui { class Widget; }
QT_END_NAMESPACE

class Widget : public QGraphicsView
{
    Q_OBJECT

public:
    Widget(QWidget *parent = nullptr);
    ~Widget();
private:
    Ui::Widget *ui;
    QGraphicsScene* scene;
    QGraphicsView* view;
};
#endif // WIDGET_H

widget.cpp

Widget::Widget(QWidget *parent)
    : QGraphicsView(parent)
    , ui(new Ui::Widget)
{
    ui->setupUi(this);
    scene = new QGraphicsScene(this);

    view = new QGraphicsView(this);
    view->setScene(scene);
    view->setContextMenuPolicy(Qt::CustomContextMenu);
    view->setDragMode(QGraphicsView::RubberBandDrag);
    view->setBackgroundBrush(Qt::gray);
    
    view->viewport()->installEventFilter(new SchematicDesign()); //Error
}        
    

SchematicDesign.h

class SchematicDesign : public QGraphicsRectItem
public:
    explicit SchematicDesign();

    explicit SchematicDesign(qreal x, qreal y, qreal width, qreal height,QGraphicsItem *parent = nullptr)
        : QGraphicsRectItem(x, y, width, height, parent)
        {}
public:
    bool eventFilter(QObject *watched, QEvent *event);
};

Schematicdesign.cpp

SchematicDesign::SchematicDesign(){}

bool SchematicDesign::eventFilter(QObject *watched, QEvent *event)
{
    bool filterEvent = false;
     
      switch(event->type()) {
     
          case QEvent::MouseButtonPress:
          {
            QMouseEvent * mouseEvent = static_cast<QMouseEvent *>(event);
            rubberBandOrigin = mouseEvent->pos();
            rubberBandActive = true;
            break;
          }
     
     
          case QEvent::MouseButtonRelease:
          {
            if (rubberBandActive) {
              QMouseEvent * mouseEvent = static_cast<QMouseEvent *>(event);
              QPoint rubberBandEnd = mouseEvent->pos();
     
              QGraphicsView * view = static_cast<QGraphicsView *>(watched->parent());
              QRectF zoomRectInScene = QRectF(view->mapToScene(rubberBandOrigin),
                                              view->mapToScene(rubberBandEnd));
     
              view->fitInView(zoomRectInScene, Qt::KeepAspectRatio);
              rubberBandActive = false;
            }
            break;
          }
      }
     
      return filterEvent;
}

How to solve this issue ? Any help will be appreciated.