Mouse event on a QGraphicsItem that is not in it's own class

[xzyerasu]

Let's say I create a QGraphicsItem (rectangle) in a QGraphicsScene (scene), without creating a class for the item:

Constructur of Mainwindow (.cpp):

ui->setupUi(this);
    scene = new QGraphicsScene(this);
    ui->graphicsView->setScene(scene);
    rectangle = scene->addRect(0,0,100,100);

ui->setupUi(this);
    scene = new QGraphicsScene(this);
    ui->graphicsView->setScene(scene);
    rectangle = scene->addRect(0,0,100,100);

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Is there a way to overwrite a mouse click on the rectangle and make something happen, even if it is not in another class?
What about showing a tooltip when hovering over it?

I hope the question is clear and not completely redundant.