Retrieving the id of a QML object in C++ code with a call to QObject::objectName() only works if there are quotes around the id name in the QML source. Yet, examples in the QML documentation do not have quotes around id names.

Rectangle
{
id: hello // This id is NOT retrievable via a C++ call to QObject::objectName()...
}

Rectangle
{
id: "hello" // ...but this one is.
}