QQuickListView: Do not re-parent existing contexts

If we're not creating a new context, we should not re-parent it.
Otherwise it gets deleted in unexpected moments.

Amends commit 471c909a68.

Pick-to: 6.5 6.6
Fixes: QTBUG-115106
Change-Id: Ib51d80dda07096587c64ac2262d115ea08855cd2
Reviewed-by: Fabian Kosmale <fabian.kosmale@qt.io>
Reviewed-by: Qt CI Bot <qt_ci_bot@qt-project.org>

src/quick/items/qquicklistview.cpp

@@ -1094,7 +1094,8 @@ QQuickItem * QQuickListViewPrivate::getSectionItem(const QString &section)
             } else if (!reuseExistingContext) {
                 context->setContextProperty(QLatin1String("section"), section);
             }
-            QQml_setParent_noEvent(context, nobj);
+            if (!reuseExistingContext)
+                QQml_setParent_noEvent(context, nobj);
             sectionItem = qobject_cast<QQuickItem *>(nobj);
             if (!sectionItem) {
                 delete nobj;

tests/auto/quick/qquicklistview2/data/delegateContextHandling.qml

@@ -0,0 +1,75 @@
+pragma ComponentBehavior: Bound
+
+import QtQuick
+import QtQuick.Window
+
+Item {
+    id: win
+    height: 640
+    width: 480
+
+    property string currentModel: 'foo'
+
+    function toggle() : Item {
+        var ret = listView.itemAtIndex(0);
+        win.currentModel = win.currentModel === 'foo' ? 'bar' : 'foo'
+
+        switch (win.currentModel) {
+        case 'foo':
+            if (listView.model) {
+                listView.model.destroy()
+            }
+            listView.model = fooModelComponent.createObject(win)
+            break
+
+        case 'bar':
+            if (listView.model) {
+                listView.model.destroy()
+            }
+            listView.model = barModelComponent.createObject(win)
+            break
+        }
+
+        return ret;
+    }
+
+    Component {
+        id: fooModelComponent
+        ListModel {
+            ListElement { textValue: "foo1" }
+        }
+    }
+
+    Component {
+        id: barModelComponent
+        ListModel {
+            ListElement { textValue: "bar1" }
+        }
+    }
+
+    ListView {
+        states: [
+            State {
+                when: win.currentModel === 'bar'
+                PropertyChanges {
+                    listView.section.property: 'sectionProp'
+                }
+            }
+        ]
+
+        id: listView
+        model: fooModelComponent.createObject(win)
+        anchors.fill: parent
+
+        section.delegate: Text {
+            required property string section
+            text: section
+        }
+
+        delegate: Text {
+            id: delg
+            text: delg.textValue
+            required property string textValue
+        }
+    }
+}

tests/auto/quick/qquicklistview2/tst_qquicklistview2.cpp

@@ -56,6 +56,8 @@ private slots:
     void sectionGeometryChange();
     void areaZeroviewDoesNotNeedlesslyPopulateWholeModel();
 
+    void delegateContextHandling();
+
 private:
     void flickWithTouch(QQuickWindow *window, const QPoint &from, const QPoint &to);
     QScopedPointer<QPointingDevice> touchDevice = QScopedPointer<QPointingDevice>(QTest::createTouchDevice());
@@ -1022,6 +1024,22 @@ void tst_QQuickListView2::areaZeroviewDoesNotNeedlesslyPopulateWholeModel()
     QVERIFY(delegateCreationCounter() < 100);
 }
 
+void tst_QQuickListView2::delegateContextHandling()
+{
+    QQmlEngine engine;
+    QQmlComponent c(&engine, testFileUrl("delegateContextHandling.qml"));
+    QVERIFY2(c.isReady(), qPrintable(c.errorString()));
+    std::unique_ptr<QObject> o(c.create());
+    QVERIFY(o);
+
+    for (int i = 0; i < 10; ++i) {
+        QQuickItem *delegate = nullptr;
+        QMetaObject::invokeMethod(o.get(), "toggle", Q_RETURN_ARG(QQuickItem *, delegate));
+        QVERIFY(delegate);
+    }
+
+}
+
 QTEST_MAIN(tst_QQuickListView2)
 
 #include "tst_qquicklistview2.moc"