21_expose_singleton_from_cpp.cpp

#include <QGuiApplication>
#include <QQmlApplicationEngine>
#include <backend.h>

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

    auto backend = new Backend(&app);
    qmlRegisterSingletonInstance<Backend>("Cemb.Backend", 1, 0, "Backend", backend);

    QQmlApplicationEngine engine;
    const QUrl url(QStringLiteral("qrc:/main.qml"));
    QObject::connect(&engine, &QQmlApplicationEngine::objectCreated,
                     &app, [url](QObject *obj, const QUrl &objUrl) {
        if (!obj && url == objUrl)
            QCoreApplication::exit(-1);
    }, Qt::QueuedConnection);
    engine.load(url);

    return app.exec();
}