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

[Guido Seifert]

QGraphicsItem is a QObject. To delete Objects with 'delete' is a 
risky game. Better use deleteLater().

Guido


On Thu, Nov 29, 2012 at 12:33:58PM +0100, 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
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