Detecting when a QGraphicsItem's boundingRect has changed

Asperamanca

I am looking for a clean way to detect when the boundingRect of a QGraphicsItem subclass has changed, or is about to change.

What I have found so far:

-) prepareGeometryChange is not virtual, therefore I should not subclass it (why, oh why is that one not virtual!?)
-) The itemChange event has everything BUT the boundingRect. I could track a change in position, but if only the size changes, I wouldn't get an event, according to the docs

Other ideas?

MaQzma

You are the only one that change the boundingRect (calling prepareGeometryChange), so after you call prepareGeometryChange you could call an other function that does all what you want.

Asperamanca

For a QGraphicsTextItem, I doubt that. It automatically seems to enlarge depending on how much text you put into it.

andre

Hmmm... I would have expected that

setting the QGraphicsItem::ItemSendsGeometryChanges flag on your graphics item, and

reimplement the itemChange() method of your QGraphicsItem

would do the trick, but it seems there is no QGraphicsItem::ItemSizeHasChanged value available. Weird... Good question!

MaQzma

If your item is a QGraphicsTextItem, its easy; every QGraphicsTextItem have a QTextDocument, so you can connect the signal "contentsChanged()":http://doc.qt.nokia.com/4.7-snapshot/qtextdocument.html#contentsChanged with a slot that do what you want.

@
QObject::connect(QGraphicsTextItem::document(), SIGNAL(contentsChanged()),
this, SLOT(doSomething()));
@

[quote author="Asperamanca" date="1341213416"]For a QGraphicsTextItem, I doubt that. It automatically seems to enlarge depending on how much text you put into it.
[/quote]

andre

Note that, while that may serve the purpose of the TS, it is not a real solution. A new text might have the same size, after all.

MaQzma

Mmm I dont understand what TS mean. We want to detect when boundingRect has changed does not matter if the boundingRect has the same size. Or yes?

Asperamanca

@Mario: Thanks for the hint regarding QGraphicsTextItem. It might be a useful workaround, if nothing comes up that works for all QGraphicsItem subclasses.