QML component enum class property

Question

I have delegate component in a separate qml file, in which I'd like to have a property which is an enum class type coming from a c++ QObject. Is this possible?

Here is a Minimum (non)Working Example:

card.h

#include <QObject>

class Card : public QObject
{
    Q_OBJECT
public:
    explicit Card(QObject *parent = 0);

    enum class InGameState {
        IDLE,
        FLIPPED,
        HIDDEN
    };
    Q_ENUM(InGameState)

private:
    InGameState mState;
};
Q_DECLARE_METATYPE(Card::InGameState)

main.cpp

#include <QGuiApplication>
#include <QQmlApplicationEngine>
#include "card.h"
int main(int argc, char *argv[])
{
    QGuiApplication app(argc, argv);

    qmlRegisterType<Card::InGameState>("com.memorygame.ingamestate", 1, 0, "InGameState");
    QQmlApplicationEngine engine;
    engine.load(QUrl(QStringLiteral("qrc:/main.qml")));

    return app.exec();
}

testcard.qml

import QtQuick 2.0
import com.memorygame.ingamestate 1.0

Item {
    property InGameState state

    Rectangle {
        id: dummy
        width: 10
    }
}

Compiler error I get:

D:\Programs\Qt\Qt5.7.0\5.7\mingw53_32\include\QtQml\qqml.h:89: error: 'staticMetaObject' is not a member of 'Card::InGameState' const char *className = T::staticMetaObject.className(); \

The enum class in not a QObject, that's why I get this error, right? But shouldn't Q_ENUM macro makes it available in the MetaSystem?

Could you please help me with this out? I could drop enum class, and change it to enum, and use an int property in qml, but I would like to use c++11 features.

Answer 1

According to the documentation,

To use a custom enumeration as a data type, its class must be registered and the enumeration must also be declared with Q_ENUM() to register it with Qt's meta object system.

So you need to register your class Card instead of the enum InGameState:

qmlRegisterType<Card>("com.memorygame.card", 1, 0, "Card");

Additionally:

The enumeration type is a representation of a C++ enum type. It is not possible to refer to the enumeration type in QML itself; instead, the int or var types can be used when referring to enumeration values from QML code.

For example, in your case, the enum should be use as follows:

import QtQuick 2.0
import com.memorygame.card 1.0

Item {
    property int state: Card.FLIPPED

    Rectangle {
        id: dummy
        width: 10
    }
}