Assigning or changing int property using enum inside QML

Question

Consider this simple enum class:

#include <QObject>
class BookTypes : public QObject
{
    Q_GADGET
    Q_ENUMS(AllBooksType)    

public:

    enum AllBooksType{
        eMagazine,
        eReference,
        eTextBook,
        eThesis
    };

signals:

public slots:

};

Type registration in main()

qmlRegisterUncreatableType<BookTypes>("trial", 1, 0, "BookTypes", 
"Don't create qml instance for BookTypes");

And this is sample QML:

Rectangle {
        id: rect
        x: 100; y: 100
        width: 100
        height: 70
        color: "PowderBlue"
        border.color: "RoyalBlue"
        border.width: 1
        radius: 3

        MouseArea{
            x: 0; y: 0
            height: parent.height
            width: parent.width
            property int bt: BookTypes.eTextBook //perfect. now bt is 2
            onClicked: {
                console.debug("old book type:- ")
                console.debug(bt) //prints 2
                console.debug("selected book type:- ")
                bt = BookTypes.eReference //gives error - why ?
                console.debug(BookTypes.eReference) //prints 'undefined'
                console.debug(bt)
            }
        }
    }

This means that the enum is properly exposed, since it initializes bt successfully in

property int bt: BookTypes.eTextBook

What I don't understand is: why it is not accessible when I try to replace value of bt in handler:

bt = BookTypes.eReference //gives error - why ?

How do I pass such an enum as an argument of Q_INVOKABLE method, for instance:

console.debug(BookTypes.eReference) //prints 'undefined'
SomeObj.someCPPMethod(BookTypes.eReference) // sends 'undefined' and defaults to 0

Answer 1

Taken from the docs:

Note: The names of enum values must begin with a capital letter in order to be accessible from QML.

Which does beg the question: Why does it work in the property binding? I've no idea, probably a Qt bug.