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

[Jan Kundrát]

On Thursday, 29 November 2012 12:33:58 CEST, Volker Poplawski wrote:
>   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;
>   }

When you call removeItem, its children are removed from the scene as well; when you delete it, these children will be deleted immediately, too. Are you sure that none of the items in your m_items is a child of any item present earlier in that list?

Have you tried to run your program under valgrind?

And as a style suggestion, it might be better to rework the loop like this:

  Q_FOREACH(QGraphicsItem *item, m_items) {
    m_scene->removeItem(item);
    delete item;
  }
  m_items.clear();

QList very likely doesn't have much overhead even when used in this way, but it feels wrong to keep deleting a first item from a container which is not a linked list.

> The interesting things is that without the removeItem() call, 
> i.e. just calling delete on the items, my program does not 
> crash.

This is interesting.

Cheers,
Jan