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POQT 4.5 - QGraphicsItem is assigned to parent scene of 0x0
 

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  1. POQT 4.5 - QGraphicsItem is assigned to parent scene of 0x0
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    <p>This is a rather strange situation here. I have a class which derived from QGraphicsScene</p> <pre><code>class DrawingScene : public QGraphicsScene { ... } </code></pre> <p>Whenever I add any item within the derived class, the item ended up attaching to a parent of 0x0. The thing is that despite that, the graphics item appearing within the scene as normal, and can be interacted with. For instance, this snippet of code:</p> <pre><code>QGraphicsEllipseItem * newEllipse = addEllipse(rect, pen); qDebug() &lt;&lt; "Scene info " &lt;&lt; this newEllipse-&gt;setPos(pos); newEllipse-&gt;setZValue(100); qDebug() &lt;&lt; "New point added = " &lt;&lt; newEllipse; </code></pre> <p>Here are some depug output</p> <pre><code>Scene info DrawingScene(0x1d2ffb8) New point added = QGraphicsItem(this = 0x3f0fda0 , parent = 0x0 , pos = QPointF(326, 307), z =100, flags = {"isVisible|isEnabled" }) </code></pre> <p>And whenever I try to delete the item, I get a warning that the scene is different, but the item is gone nonetheless.</p> <p>Am I missing something, or is QGraphicsScene not meant to be derived from in the first place?</p> <p><strong>Edit: Code for deletion</strong></p> <p>The QGraphicsItems, are added to QMap for fast mapping purpose and to disable a group of them at a go. So this is how the item is added to the scene (as above) and the Map</p> <pre><code>int SceneTrackerData::addLink(QGraphicsLineItem * newLink) { links_.insert(currentLinkID_, newLink); qDebug() &lt;&lt; links_; // Store the ID of the newly added link and increment link count int thisLinkID = currentLinkID_; currentLinkID_++; newLink-&gt;setData(LinkData::LinkID, QVariant(thisLinkID)); qDebug() &lt;&lt; "Link " &lt;&lt; thisLinkID &lt;&lt; " connecting " &lt;&lt; newLink-&gt;data(0).toInt() &lt;&lt; " and " &lt;&lt; newLink-&gt;data(1).toInt() &lt;&lt; " added."; return thisLinkID; } </code></pre> <p>Here's the deletion:</p> <p>SceneManager contains an instance of DrawingScene, which inherits QGraphicsScene</p> <pre><code>void SceneManager::DeleteLink(int linkID, int startNodeID, int endNodeID) { // sceneData_ wraps the QMap&lt;int, QGraphicsItem&gt;. // This calls SceneTrackerData::deleteLink(int) (below) QGraphicsLineItem * link = sceneData_-&gt;deleteLink(linkID); qDebug() &lt;&lt; "Link to remove " &lt;&lt; link; // scene_ is an instance of DrawingScene, which inherits QGraphicsItem, so // this is just a vanila call to QGraphicsScene::removeItem() scene_-&gt;removeItem(link); // release the link from memory delete link; emit informLinkDeleted(startNodeID, endNodeID); } QGraphicsLineItem* SceneTrackerData::deleteLink(int linkid) { qDebug() &lt;&lt; "deleting link of id " &lt;&lt; linkid; QGraphicsLineItem * line = links_.take(linkid); qDebug() &lt;&lt; links_; return line; } </code></pre> <p>The warning is </p> <blockquote> <p>QGraphicsScene::removeItem: item 0x32fa7d8's scene (0x0) is different from this scene (0x1aabb60)</p> </blockquote> <p><strong>More edits</strong></p> <p>After adding some lines and ellipse items, this is how the scene->items() looks like after adding the objects. They all have parent = 0x0</p> <pre><code>(QGraphicsItem(this =0x3b980a8, parent =0x0, pos =QPointF(0, 0), z =-1, flags = {"isVisible|isEnabled" }), QGraphicsItem(this =0x3c32980, parent =0x0, pos =QPointF(326, 303), z =100, flags = {"isVisible|isEnabled" }), QGraphicsItem(this =0x3b9a1e0, parent =0x0, pos =QPointF(420, 410), z =100, flags = {"isVisible|isEnabled" }), QGraphicsItem(this =0x3f0ffc0, parent =0x0, pos =QPointF(411, 395), z =100, flags = {"isVisible|isEnabled" }), QGraphicsItem(this =0x3cf4600, parent =0x0, pos =QPointF(327, 302), z =0, flags = {"isVisible|isEnabled" })) </code></pre> <p>What I am trying to delete is QGraphicsItem(this =0x3cf4600), and here's the outcome:</p> <pre><code>Link to remove QGraphicsItem(this = 0x3cf4600 , parent = 0x0 , pos = QPointF(327, 302), z =0, flags = {"isVisible|isEnabled" }) Before removing: QGraphicsScene::removeItem: item 0x3cf4600's scene (0x0) is different from this scene (0x1e2ffb8) Scene after moving (QGraphicsItem(this =0x3b980a8, parent =0x0, pos =QPointF(0, 0), z =-1, flags = {"isVisible|isEnabled" }), QGraphicsItem(this =0x3c32980, parent =0x0, pos =QPointF(326, 303), z =100, flags = {"isVisible|isEnabled" }), QGraphicsItem(this =0x3b9a1e0, parent =0x0, pos =QPointF(420, 410), z =100, flags = {"isVisible|isEnabled" }), QGraphicsItem(this =0x3f0ffc0, parent =0x0, pos =QPointF(411, 395), z =100, flags = {"isVisible|isEnabled" })) </code></pre> <p>The behaviour is correct. I am puzzled why the warning is evening triggered at all.</p>
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