Ok Let me say , what i want to achieve. I am studying an API where they have subclassed the QGraphicsView. It is possible to drag graphics item into the view . Now I wan to connect two items with an arrow. The arrow is only drawn when the mouse is moved from one item to the other item while the Ctrl button is down. Now i think that i have to over-ride the mouseMoveEvent with the modifiers() . What do you think?
That sounds reasonable to me.

To achieve this do i have to subclass QGraphicsScene as well or it will be fine if i over-ride the mouseMoveEvent() function in the QGraphicsView subclass - which is already done.
I guess it depends on whether you want to have specialized data in your scene. If you are absolutely sure you are not going to modify your scene but just extend your view then I guess subclassing QGraphicsScene is not necessary. Having said that I think it's not too late if you subclass the QGraphicsScene when you need to I guess sometimes it is better to kick off the journey to figure out which way you are going rather than sitting in the room and falling into the endless worrying and "what-if" questions.

Regards,