- 
    Bug 
- 
    Resolution: Fixed
- 
    P2: Important 
- 
    6.8
- 
        8fc186e1a (dev), 643426716 (dev), 5db17816f (6.9), b61bd7cb3 (6.9), 6e1577cfa (6.8), 0913fe1c1 (6.8), a48071da9 (dev), 7c8eed416 (6.9), d2bb2002f (6.8)
- 
        framework-content 4, framework-content 5, framework-content 6
Any usage of QQmlListProperty requires accessing the inner object / data fields. But those fields are undocumented: https://doc.qt.io/qt-6/qqmllistproperty.html
The example https://doc.qt.io/qt-6/qtqml-tutorials-extending-qml-example.html#chapter-5-using-list-property-types shows the fields being accessed:
void PieChart::append_slice(QQmlListProperty<PieSlice> *list, PieSlice *slice)
{
    PieChart *chart = qobject_cast<PieChart *>(list->object); // <-- here
    if (chart) {
        slice->setParentItem(chart);
        chart->m_slices.append(slice);
    }
}