Setting boundingRect() for a custom QGraphicsObject drawn using mouse

[MarKS]

I want to draw a custom rectangle when dragged using a mouse events. Since i need additional features like resizing the rectangle, contextMenuEvents() and other stuff, i subclassed QGraphicsObject and overriden pure virtual functions. Moreover, i have a subclassed QGraphicsScene which handles mouse events.

What do i want:

To be able to draw custom rectangle when mouse events are triggered on QGraphicsScene. Like left mouse button->drag.
Drawing it simply using QGraphicsRectItem works fine.

Problem:

How to set boundingRect() of my custom rectangle and paint() or update the rectangle as the mouse moves on the QGraphicsScene?

Currently, i have an empty subclassed RectItem. Which looks like this:

RectItem::RectItem(QObject* parent) :
    QGraphicsObject()
{

}

QRectF RectItem::boundingRect() const
{
      // how to set bounding rect when rectangle is drawn dynamically using mouse?
}

void RectItem::paint(QPainter* painter, const QStyleOptionGraphicsItem* option, QWidget* widget)
{
     // how to update paint() and show a rectangle to the user?
}

How to implement both boundingRect() and paint()?