Qt QML Access a QObject by a String - c++

Question

I have a Model which is exposed to the qml context property and it contains a List of Lists. These Lists are created dynamically and are then exposed to the qml context as well.
Model:
#include <QtCore>
#include <QQmlContext>
class Model : public QObject
{
Q_OBJECT
public:
Model(QQmlContext* rootContext) {
rootContext->setContextProperty(QML_NAME, this);
dataLists.push_back( new DatedValueList(rootContext, "List1", "m"));
names.push_back("List1");
}
QList<DatedValueList*> dataLists;
QString QML_NAME = "Model";
QList<QString> names;
Q_INVOKABLE QList<QString> getListNames() { return names };
};
DatedValueList:
#include <QObject>
#include <QtCore>
#include <QQmlContext>
class DatedValueList: public QObject, public QList<int>
{
Q_OBJECT
public:
DatedValueList(QQmlContext* rootContext, QString i_name, QString i_unit) : name(i_name), unit(i_unit)
{
rootContext->setContextProperty(name, this);
}
QString name; //under this name it is exposed
QString unit;
Q_INVOKABLE QString getName() {return name;}
Q_INVOKABLE QString getUnit() {return unit;}
};
Main:
#include <QtCore>
#include <QQmlContext>
#include <QGuiApplication>
#include <QQmlApplicationEngine>
int main(int argc, char *argv[])
{
QGuiApplication app(argc, argv);
QQmlApplicationEngine engine;
//create Controller w/ thread
QQmlContext* rootContext = engine.rootContext();
Model model(rootContext );
//load QML into engine
engine.load(QUrl(QStringLiteral("qrc:/resource/qml/MainWindow.qml")));
return app.exec();
}
in QML I now want to access one of these DatedValueLists like this. MainWindow.qml:
import QtQuick 2.15
import QtQuick.Window 2.15
Window {
id: mainview
width: 1800
height: 768
visible: true
flags: Qt.Window
Timer {
interval: 1000 // 1 Hz
running: true
repeat: true
onTriggered: {
console.log( Model.getListNames()[0] ) // Output: List1
console.log( Model.getListNames()[0].getUnit() ) // Not working
}
}
}
The second output line is not working. It is a String and I want to call a function of on it. But how can I cast it or use the String as a qml context id?

Answer 1

As minimal requirement you will have to implement a function that returns the DatedValueList on your Model class:
Q_INVOKABLE DatedValueList getList(const QString& name) { return ... };
But this immediately poses a small challenge, since your data structure does not allow lookup and thus should iterate the whole dataLists member.
I think you are better of providing a QVariantMap from your Model class, you can give a name to each list and also obtain the list itself:
//C++
Q_PROPERTY(QVariantMap listMap ...)
//QML
model.listMap.keys()[0]
model.listMap[model.listMap.keys()[0]].getUnit()
But this can even be a bad decision depending on how you want to shape the rest of your UI, which I'm most sure will not be console.log's only ;-)
Another note, context properties should not have a capital for the first letter. You are likely instantiating a Model inside the console.log call instead of referencing the one instantiate in main