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c++qt5qgraphicsitemqgraphicsscene

Crash after QGraphicsScene::removeItem() with custom item class

I am populating a QGraphicsScene with instances of a custom item class (inherting QGraphicsPathItem). At some point during runtime, I try to remove an item (plus its children) from the scene by calling:

delete pItem;

This automatically calls QGraphicsScene::removeItem(), however it also leads to a crash in the class QGraphicsSceneFindItemBspTreeVisitor during the next repaint.

Solution

  • TL;DR: The solution is to ensure that QGraphicsItem::prepareGeometryChange() gets called before the item's removal from the scene.

    The problem is that during the item removal from the scene, the scene internal index was not properly updated, resulting in the crash upon the next attempt of drawing the scene.

    Since in my case, I use a custom subclass from QGraphicsPathItem, I simply put the call to QGraphicsItem::prepareGeometryChange() into its destructor since I am not manually removing the item from the scene (via QGraphicsScene::removeItem()), but instead I simply call delete pItem; which in return triggers the item's destructor as well as removeItem() later on.