Access `QMap<K,V>` "where V QObject` from qml

paulpv

I have a fairly basic Hello World Qt Quick Application (Qt+Qml) at:
https://github.com/paulpv/QtQmlHelloQVariantMap/

In it I am trying to [learn how to] expose a QMap<K,V> to qml (read-only is fine for now).
My end-goal is to expose a QMap<int, HotkeyInfo>, where HotkeyInfo is defined as:

class HotkeyInfo : public QObject
{
    Q_OBJECT
    ...
    Q_PROPERTY(QString computerName MEMBER m_computerName)
    Q_PROPERTY(QString appName MEMBER m_appName)
    ...
private:
    QString m_computerName;
    QString m_appName;
};

using MapHotkeys = QMap<QString, QVariant>;

class HotkeyManager : public QObject
{
    Q_OBJECT
    ...
    Q_PROPERTY(MapHotkeys hotkeys MEMBER m_hotkeys)

    void add(const int key, HotkeyInfo* hotkeyInfo) {
        m_hotkeys[QString::number(key)] = QVariant::fromValue(hotkeyInfo);
    }

    void remove(const int key) {
        auto hotkeyInfo = m_hotkeys.take(QString::number(key)).value<HotkeyInfo*>();
        if (hotkeyInfo != nullptr) {
            delete hotkeyInfo;
        }
    }
    ...
private:
    MapHotkeys m_hotkeys;
}

I populate the Map with:

void initializeMessages(HotkeyManager& hotkeyManager)
{
    // Ignore NewDeleteLeaks; ~HotkeyManager frees all added HotkeyInfos.
    hotkeyManager.add(1, new HotkeyInfo("computer1", "app2"));
    hotkeyManager.add(2, new HotkeyInfo("computer2", "app4"));
}

Qml code to read the HotkeyInfo properties...

import QtQuick
import QtQuick.Window

ApplicationWindow {
    width: 640
    height: 480
    visible: true
    title: qsTr("Hello World")

    Component.onCompleted: {
        console.log(`Component.onCompleted`)
        console.log(`hotkeyManager=${hotkeyManager}`)
        var hotkeys = hotkeyManager.hotkeys
        console.log(`hotkeys=${hotkeys}`)
        var hotkeyInfo1 = hotkeys[1]
        console.log(`hotkeyInfo1=${hotkeyInfo1}`)
        console.log(`hotkeyInfo1.computerName=${hotkeyInfo1.computerName}`)
        console.log(`hotkeyInfo1.appName=${hotkeyInfo1.appName}`)
        var hotkeyInfo2 = hotkeys[2]
        console.log(`hotkeyInfo2=${hotkeyInfo2}`)
        console.log(`hotkeyInfo2.computerName=${hotkeyInfo2.computerName}`)
        console.log(`hotkeyInfo2.appName=${hotkeyInfo2.appName}`)
    }
}

My qml can see properties of the HotkeyInfo class just fine if I use QMap<String,QVariant> and convert the key to and from an int and values to and from HotkeyInfo*.

qml: Component.onCompleted
qml: hotkeyManager=HotkeyManager(0x930095fb78)
qml: hotkeys=[object Object]
qml: hotkeyInfo1=HotkeyInfo(0x263748f66a0)
qml: hotkeyInfo1.computerName=computer1
qml: hotkeyInfo1.appName=app2
qml: hotkeyInfo2=HotkeyInfo(0x263748f6520)
qml: hotkeyInfo2.computerName=computer2
qml: hotkeyInfo2.appName=app4

I am naive enough to think that I should not have to add extra code to convert to/from key and value types, and/or think that doing that means I might be doing something wrong; I would like to remove that extra code.

If I just change the map to QMap<QString,HotkeyInfo*> then it can no longer access the map entries (ie: "stops working")

qml: Component.onCompleted
qml: hotkeyManager=HotkeyManager(0x16e5cff978)
qml: hotkeys=QVariant(QMap<QString,HotkeyInfo*>, QMap(("1", HotkeyInfo(0x1b975ff7800))("2", HotkeyInfo(0x1b975ff8500))))
qml: hotkeyInfo1=undefined
qrc:/qt/qml/QtQmlHelloQVariantMap/Main.qml:21: TypeError: Cannot read property 'computerName' of undefined

NOTE that the debug output still shows it knows the object types well enough to toString() them.

If I just change the map to QMap<int,QVariant> then strangely also stops working.

qml: Component.onCompleted
qml: hotkeyManager=HotkeyManager(0x22c22ff618)
qml: hotkeys=QVariant(QMap<int,QVariant>, QMap((1, QVariant(HotkeyInfo*, 0x1314e128ac0))(2, QVariant(HotkeyInfo*, 0x1314e1294c0))))
qml: hotkeyInfo1=undefined
qrc:/qt/qml/QtQmlHelloQVariantMap/Main.qml:21: TypeError: Cannot read property 'computerName' of undefined

Interestingly, the qml code has no problem accessing the working QMap<String,QVariant> values using an int key; something seems to auto-convert that to a string.
It seems odd that an int key does not work on a QMap<int,QVariant>, but an int key does work on a QMap<String,QVariant>.

If I change the map to QMap<int,HotkeyInfo*> then it obviously also stops working.

qml: Component.onCompleted
qml: hotkeyManager=HotkeyManager(0xf7969afb58)
qml: hotkeys=QVariant(QMap<int,HotkeyInfo*>, QMap((1, HotkeyInfo(0x2a033aeaab0))(2, HotkeyInfo(0x2a033ae8cb0))))
qml: hotkeyInfo1=undefined
qrc:/qt/qml/QtQmlHelloQVariantMap/Main.qml:21: TypeError: Cannot read property 'computerName' of undefined

Can anyone suggest how to accomplish reading a QMap<?,QObject> from qml?

AI chatbots seem useless on this.

Thanks!

Pv