How to scale an object which inherit QGrahicsItem within it's parent QGraphicsItem

[wysota]

And I don't catch your mean for i don't know how to use QGraphicsItem::itemChange() to signal it's size change to it's parent item. Should I use QGraphicsItem::ItemTransformHasChanged or QGraphicsItem::ItemPositionChange
as a parameter of QGraphicsItem::itemChange() ?

Use ItemTransformChange so that you can return a new transformation.

And could you provide me with source code on this ! Thank you very much!

There is a nice example in the itemChange() documentation, only that it monitors the position and not the transformation of the item.