set parent when creating a QML component from C++

[lqsa]

Hello,

I've a QML component that is created from C++ code:

QML code:

Rectangle {
    width: parent.width
    y: parent.height / 2
    color: "red"
}

Rectangle {
    width: parent.width
    y: parent.height / 2
    color: "red"
}

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QQmlComponent component(engine, QUrl(src));
QObject *comp = component.create();
QQuickItem *item = qobject_cast<QQuickItem*>(comp);
item->setParentItem(root);

QQmlComponent component(engine, QUrl(src));
QObject *comp = component.create();
QQuickItem *item = qobject_cast<QQuickItem*>(comp);
item->setParentItem(root);

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When the component is created appears these errors:

TypeError: Cannot read property 'height' of null
TypeError: Cannot read property 'width' of null

On creation, the parent property is null and not is valid until the item->setParentItem is executed. How can I set the parent item when creating the component? or how to avoid these errors?

Best regards.