[Interest] QGraphicsScene crash after removeItem() and delete item

[Constantin Makshin]

Well, after following the link Volker gave me
(http://code.woboq.org/kde/qt4/src/) and looking at the code related to
removing/deleting QGraphicsItem-s I admit my guess was too random. :)

On 11/29/2012 06:53 PM, Constantin Makshin wrote:
> QGraphicsScene::removeItem() documentation says "Removes the item item
> and all its children from the scene."
> 
> So here is my random guess:
> You remove an item which has at least one child. Some time later you
> call QGraphicsScene::removeItem() on one of its children and, since it's
> not part of the scene anymore, get a crash.
> 
> I can't check this guess because Gitorious doesn't want to show the
> contents of qgraphicsscene.cpp and I'm too lazy to download the whole Qt
> tarball. :)
> 
> On 11/29/2012 03:33 PM, Volker Poplawski wrote:
>> Hi everybody,
>>
>> I'm facing segfault in succession of deleting a number of QGraphicsItems from a scene.
>>
>> The following code leads to the stack trace below on the next redraw of the scene.
>>
>>   while (not m_items.isEmpty())
>>   {
>>     QGraphicsItem *item = m_items.takeFirst();
>>     m_scene->removeItem(item);  // qtdoc says it's faster to remove item first then delete
>>     delete item;
>>   }
>>
>> The interesting things is that without the removeItem() call, i.e. just calling delete on the items, my program does not crash.
>>
>> 0	QGraphicsSceneFindItemBspTreeVisitor::visit(QList<QGraphicsItem*>*)			0x1075cff	
>> 1	QGraphicsSceneBspTree::climbTree(QGraphicsSceneBspTreeVisitor*, QRectF const&, int) const			0x1074c40	
>> 2	QGraphicsSceneBspTree::climbTree(QGraphicsSceneBspTreeVisitor*, QRectF const&, int) const			0x1074ce0	
>> 3	QGraphicsSceneBspTree::climbTree(QGraphicsSceneBspTreeVisitor*, QRectF const&, int) const			0x1074c40	
>> 4	QGraphicsSceneBspTree::climbTree(QGraphicsSceneBspTreeVisitor*, QRectF const&, int) const			0x1074c40	
>> 5	QGraphicsSceneBspTree::climbTree(QGraphicsSceneBspTreeVisitor*, QRectF const&, int) const			0x1074c40	
>> 6	QGraphicsSceneBspTree::climbTree(QGraphicsSceneBspTreeVisitor*, QRectF const&, int) const			0x1074c40	
>> 7	QGraphicsSceneBspTree::climbTree(QGraphicsSceneBspTreeVisitor*, QRectF const&, int) const			0x1074c40	
>> 8	QGraphicsSceneBspTree::climbTree(QGraphicsSceneBspTreeVisitor*, QRectF const&, int) const			0x1074c40	
>> 9	QGraphicsSceneBspTree::climbTree(QGraphicsSceneBspTreeVisitor*, QRectF const&, int) const			0x1074ce0	
>> 10	QGraphicsSceneBspTree::items(QRectF const&, bool) const			0x107539e	
>> 11	QGraphicsSceneBspTreeIndexPrivate::estimateItems(QRectF const&, Qt::SortOrder, bool)			0xf24058	
>> 12	QGraphicsSceneBspTreeIndex::estimateTopLevelItems(QRectF const&, Qt::SortOrder) const			0xf24233	
>> 13	QGraphicsScenePrivate::drawItems(QPainter*, QTransform const*, QRegion*, QWidget*)			0xf194ad	
>> 14	QGraphicsView::paintEvent(QPaintEvent*)			0xf3505c	
>> 15	QWidget::event(QEvent*)			0xa6941a	
>> 16	QFrame::event(QEvent*)			0xd81236	
>> 17	QGraphicsView::viewportEvent(QEvent*)			0xf362bb	
>> 18	QCoreApplicationPrivate::sendThroughObjectEventFilters(QObject*, QEvent*)			0x11992b7	
>> 19	QApplicationPrivate::notify_helper(QObject*, QEvent*)			0xa240f1	
>> 20	QApplication::notify(QObject*, QEvent*)			0xa2c63f	
>> ...	<More>				
>>
>> ....Volker
>> _______________________________________________
>> Interest mailing list
>> Interest at qt-project.org
>> http://lists.qt-project.org/mailman/listinfo/interest

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