Exposing already defined enum to QML

jay1

I have an enum which is already define as below:

// Defines.h file
namespace com {
enum class BookType {
SMALL = 0, BIG, UNKOWN
};
}

Above enum doesn't have a Q_NAMESPACE declared.
I created the QObject class to expose enum to QML

// Book.h file
#include "Defines.h"
namespace com {
Q_NAMESPACE
Q_ENUM_NS(BookType)
}

namespace ui {
class Book: public QObject {
Q_OBJECT
QML_ELEMENT
QML_SINGLETON
Q_PROPERTY(com::BookType type READ type WRITE setType NOTIFY onTypeChanged)
....
}
}

// Main.qml

Button {
onClicked: {
console.log(Book.BookType.BIG) // gives undefined
console.log(Book.type) // gives 1
}
}

How can access BookType enum be used in qml ?

sierdzio

What about:

console.log(BookType.BIG)

jay1

@sierdzio It prints following errors

ReferenceError: BookType is not defined
TypeError: Cannot read property 'BIG' of undefined

sierdzio

An easy but ugly way would be to change com into a stuct with Q_GADGET.

Alternatively you should be able to register the enum manually Qt5-way:

qRegisterMetaType<com::BookType>();

TomZ

enums are always a mess, basically the general idea to have a clean namespace with enums doesn't work with QML.

I'm always just going for the slightly ugly but entirely functional solution to make the namespace a QObject instead. Example:
https://codeberg.org/Flowee/pay/src/branch/master/src/WalletEnums.h

Then in your C++ you just need: qmlRegisterType<WalletEnums>("something.or.other", 1, 0, "MyEnums");

Then in your QML you need to import the first argument (something.or.other) and you can use your values in that file without problems.

jay1

I ended up creating the enum and registering it as a type.

GrecKo

@TomZ said in Exposing already defined enum to QML:

enums are always a mess, basically the general idea to have a clean namespace with enums doesn't work with QML.

It does work fine with namespaces. Q_ENUM needs to be made in the scope where the enum was defined though, it doesn't work with an already defined enum. And this requirement exists for both object/gadgets and namespaces.
The code you linked would have been fine with a namespace.

Also don't use qmlRegister*** in Qt 6, QML_*** are preferred.