c++qtqgraphicsviewqgraphicssceneqgraphicsitem

QGraphicsScene doesn't removeItem() immediately

I have a simple node graph editor in c++/Qt that uses QGraphicsView/QGraphicsScene to draw the graph and I'm experiencing a weird issue where QGraphicsItems sometimes remain on the scene for a split second after calling scene.removeItem(Item). I'm deleting the the items right after removing them from the scene so it's causing segfaults. When I comment the deletion out I can see a part of the item being drawn (not the whole thing) for a literal second before it disappears completely.
Here's my code. It's a slot that gets called by a when a connection gets removed.

void GraphScene::connectionRemoved(QUuid uuid)
{
    //Connections and nodes are stored in QMaps to retrieve them by uuid
    ConnectionGraphicsItem *connectionItem = connections.value(uuid);
    if (connectionItem == nullptr) return;
    removeItem(connectionItem); //Delayed
    //delete connectionItem;
    qDebug() << "con removed" << uuid;
}

I tried calling prepareGeometryChange() before removing the item from the scene and it didn't fix it. Setting QGraphicsView update mode to FullViewportUpdate didn't help either.

Solution

  • I've solved the problem. Qt Docs for

    void QGraphicsItem::prepareGeometryChange()

    state that you need to call this method before changing the bounding rectangle of the item so that the graphics scene updates its index. I didn't do this. So when I added this before the code that adjusts the connections to match node ports the problem disappeared.
    Edit: Also, I've realized that I don't remove the item from the QMap.