Add map items at run-time

Mark81

I'm trying to automate a bit of logic, instead of hard-write values each time.
My application may load QML pages into a QQuickWidget. Every page is different but has the same structure. There are some Text controls that have a unique name. They must show a value retrieved by the C++ backend class.

First thoughts. I defined a QVariantMap where the keys are the items' names. Once the map is filled by my C++ class the QML page can show the actual values. Something like this:

C++

public:
    Q_PROPERTY(QVariantMap data READ data NOTIFY dataChanged)
    QVariantMap data() const { return _mapData; }

private:
    QVariantMap _mapData;

signals:
    void dataChanged();

// ...

    QQmlContext *rootContext = ui->quickWidget->rootContext();
    rootContext->setContextProperty("App", this);
    ui->quickWidget->setSource(QUrl(filename));

    _mapData.insert("123", "Hello");
    _mapData.insert("124", "Hello");
    emit dataChanged();

QML

Text {
    id: txt123
    text: App.data["123"]
}

Text {
    id: txt124
    text: App.data["123"]
}

Now the problem is I have different keys for each QML page. I might define a C++ slot so the QML page can tell what keys it has:

signal qmlSignal(string msg)

function foo()
{
    qmlSignal("123,124,125")
}

and in C++ I can split the string and insert them as map keys.
It's ok but still I need to manually compile the list.

I'm looking for an automagic way, like what the QMap::operator[] does. I mean, the first time the QML object try to read a value with a given key, if this is not present it should add to the mapData. Hence, every time I refresh the values I can find new keys.

In C++ I know how to do this (using the [] operator as said) but how to do the same in QML using only the App.data[key] call?
Unfortunately the getter function doesn't allow me to retrieve the current key, otherwise it would be easy enough to check whether it exists.