SetProperty for loaded QML component without using SetContextProperty - initialization

Question

I have a C++ plugin system, where a QQmlComponent is created and a qml file is loaded when the user requests a new plugin instance.
Currently I am using setContextProperty() to tell QML about a QObject that is needed for proper initialization.
mEngine->rootContext()->setContextProperty("controller", QVariant::fromValue(mController));
mComponent = new QQmlComponent(mEngine);
mComponent->loadUrl(QUrl{ "qrc:///MyPlugin.qml" });
The problem is, when instantiating a second plugin, both will use the controller of the second one because "controller" is global in QML.
Repeater {
model: controller.numEntries
Is there a way to set a context property locally (only for the current instance)?
I found solutions using setProperty() or QQmlIncubator and setInitialState(), but they all seem to require an object that was already created from my component. But in my plugin I only define the component, which is loaded in the main application through a Loader item. So, when trying these approaches, I always ended up in setting the value in a copy of the item, but not the one being created in my backend.
How can I get access to a property of the component that is created in QML?
mComponent->findChild<QQuickItem*>("controller");
does not give me any results, even if I defined the property in MyPlugin.qml.

Answer 1

Maybe you can create a QObject based class and have a slot and instead of using property you can call slot to slot create a new property in c++ and return it to QML
ControllerCreator.h
#ifndef CONTROLLERCREATOR_H
#define CONTROLLERCREATOR_H
#include <QObject>
class ControllerCreator : public QObject {
Q_OBJECT
public:
explicit ControllerCreator(QObject *parent = nullptr);
signals:
public slots:
int propertyCreator();
private:
int m_example;
};
#endif // CONTROLLERCREATOR_H
ControllerCreator.cpp
#include "ControllerCreator.h"
ControllerCreator::ControllerCreator(QObject *parent)
: QObject(parent), m_example(0)
{
}
int ControllerCreator::propertyCreator()
{
m_example++;
return m_example;
}
main.cpp
#include <QGuiApplication>
#include <QQmlApplicationEngine>
#include <QQmlContext>
#include "ControllerCreator.h"
int main(int argc, char *argv[])
{
QCoreApplication::setAttribute(Qt::AA_EnableHighDpiScaling);
QGuiApplication app(argc, argv);
QQmlApplicationEngine engine;
ControllerCreator controllerCreator;
engine.rootContext()->setContextProperty("creator", &controllerCreator);
engine.load(QUrl(QLatin1String("qrc:/main.qml")));
if (engine.rootObjects().isEmpty())
return -1;
return app.exec();
}
main.qml
import QtQuick 2.7
import QtQuick.Controls 2.0
import QtQuick.Layouts 1.3
ApplicationWindow {
visible: true
width: 640
height: 480
title: qsTr("Hello World")
Column{
anchors.fill: parent
Text{
text: creator.propertyCreator()
color: "blue"
}
Text{
text: creator.propertyCreator()
color: "red"
}
Text{
text: creator.propertyCreator()
color: "green"
}
}
}