Cannot compare C++ enum in QML

rdeem

Hi,

I have exported a C++ enum to QML and it seems to be recognized correctly in QML. When I use the enum as a property type in another class then the property isn't compared correctly with the enum value and comparison returns false. I have added a small example below.

Class with enum

#ifndef TYPES_H
#define TYPES_H

#include <QObject>

class SystemStateClass
{
    Q_GADGET
public:
    enum SystemStateEnum {
        Idle = 0,
        MainView,
    };
    Q_ENUM(SystemStateEnum)
private:
    explicit SystemStateClass() {}
};

using SystemState = SystemStateClass::SystemStateEnum;

#endif // TYPES_H

Class with enum property

#ifndef CTRL_H
#define CTRL_H

#include <QObject>
#include "Types.h"

class Ctrl : public QObject
{
     Q_OBJECT
public:

    Ctrl() {};
    ~Ctrl() = default;
    Q_PROPERTY(SystemState state READ state NOTIFY stateChanged)
    SystemState state() { return m_state; }

signals:
    void stateChanged(SystemState);

private:
    SystemState m_state = SystemState::MainView;
};

#endif // CTRL_H

main.cpp

#include <QGuiApplication>
#include <QQmlApplicationEngine>
#include <QQmlContext>
#include "Ctrl.h"

int main(int argc, char *argv[])
{
    QCoreApplication::setAttribute(Qt::AA_EnableHighDpiScaling);
    QGuiApplication app(argc, argv);
    QQmlApplicationEngine engine;

    qRegisterMetaType<SystemState>("SystemState");
    engine.rootContext()->setContextProperty("ctrl", new Ctrl());
    qmlRegisterUncreatableType<SystemStateClass>("App.Types", 1, 0, "SystemState", "Not creatable as it is an enum type");

    engine.load("qrc:/main.qml");
    return app.exec();
}

main.qml

import QtQuick 2.14
import QtQuick.Window 2.14
import App.Types 1.0

Window {
    visible: true
    width: 640
    height: 480
    title: qsTr("Test enum")

    Component.onCompleted: {
        console.log("ctrl.state:", ctrl.state)
        console.log("Enum value:", SystemState.MainView)
        console.log("Equals enum val:", (ctrl.state === SystemState.MainView))
        console.log("Equals int:", (ctrl.state === 1))
    }
}

Output

qml: ctrl.state: MainView
qml: Enum value: 1
qml: Equals enum val: false
qml: Equals int: false

rdeem

I solved it. The type used in the Q_PROPERTY must be stated explicitly as SystemStateClass::SystemStateEnum instead of using using-declaration (or typedef) SystemState.

Q_PROPERTY(SystemStateClass::SystemStateEnum state READ state NOTIFY stateChanged)

This will allow QML to interpret the enum as int and the output will be:

qml: ctrl.state: 1
qml: Enum value: 1
qml: Equals enum val: true
qml: Equals int: true

The using-declaration SystemState can be used in all other parts of C++ code except in Q_PROPERTY.