How to receive notifications from QGraphicsScene by addItem or itemChange?

Question

In my project, I use QGraphicsScene and add / remove items throughout the code.

Now I want to receive notifications when a QGraphicsItem added or removed. Many Qt classes have notification signals, or at least virtual functions, called upon such changes. I try to avoid adding many lines of code in many places, which is not only cumbersome, but also unsafe (forgetting about inserting / deleting now or in the future).

I need a solution that works with any QGraphicsItem .

This is a list of things that don't work:

• connect to the QGraphicsScene signal ^{(as in QAbstractItemModel::rowsInserted() ) ->} no.
• inherit from QGraphicsScene and overload the virtual notifier function ^{(as in QTabWidget::tabInserted() ) ->} no.
• Inheriting and overloading addItem() , sending notifications itself ^{(as in QMdiArea::addSubWindow() )} → addItem not virtual and is called from the QGraphicsItems constructors.
• set event filters to newly added QGraphicsItems → I don’t know how to get a newly added element And it will be a sceneEventFilter , which can only be set on another QGraphicsItems .
• connect to itemChange() from QGraphicsItem → itemChange not a signal And overloading QGraphicsItem not an option.
• wrap QGraphicsScene (having the scene as a private member) and only expose the addItem and removeItem → functions, but QGraphicsItems in this scene can still be accessed through the scene() function, so this solution is not safe enough.

How can I be notified of item changes?

If there is a simple way that I just skipped, write to me. Otherwise, I would be very grateful for the ideas.

Answer 1

I think that best of all, you can connect to the QGraphicsScene::changed() signal.

It will not tell you which items have been changed / added / deleted since it is designed for QGraphicsView to update the display. But you should be able to find out using the provided areas.