Thank you for the advice.
Now I use the itemChange() function and it seems to work, but now I think how to detect index of the moved GraphicsItem and the index of the scene, so that I can update the coordinates within my point vectors.
I have got a
Qt Code: 
  1. QVector<QGraphicsScene *> vec_scenes;
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, where I pushed back several scenes. Every scene corresponds to a construct(individual) consisting of two vectors (one for x and another for y coordinates). With this I can then add a certain amount of points (graphicsitems) into the scene for every construct. I have got more than one construct (individuals) within a vector of individuals, so it is like a population. Don't be surprised, I'm working on evolutionary algorithms and want to visualize the process by means of Qt.

So, how can I update the x, y coordinates of an individual , if a graphicsitem within a scene will be moved? Any ideas?

best regards