Update QML map via C++

vmetodiev

Dear QT Community,

I have a QApplication with an embedded QQuickWidget (a map). I have managed to expose a pointer to the object that is needed to manipulate the current location. However, I cannot figure out how to update (refresh) the view with the newly set coordinates from C++.

May someone please help with this one...

Map::Map(QObject* qmlRootObject,
         QString specificObject) : QObject (Q_NULLPTR)
{
    QObject* qmlSpecificObject = qmlRootObject->findChild<QObject*>(specificObject);
    this->openStreetMap = qmlSpecificObject;
    this->openStreetMapCenterObject = qvariant_cast<QObject*>(openStreetMap->property("center"));

    // Do something
    auto coordinates = this->openStreetMap->property("center").value<QGeoCoordinate>();
    qDebug() << "Coordinates (original): " << coordinates;

    coordinates.setLatitude(coordinates.latitude() + 2);
    coordinates.setLatitude(coordinates.longitude() + 3);
    
    this->openStreetMap->setProperty("newLat", coordinates.latitude());
    this->openStreetMap->setProperty("newLon", coordinates.longitude());
    // the "center" attribute does not work as well

    qDebug() << "Coordinates (new): " << coordinates;
}

Inside main.cpp

   // Access the root object
    QQmlContext *context = engine.rootContext();
    engine.load(QUrl(QStringLiteral("../TrackServ/map.qml")));
    QObject *rootObject = engine.rootObjects().first();

    Map* map = new Map(rootObject, "osmMap");
    if (map == nullptr) {
        qDebug() << "ERROR: QML element not found...";
    }
    else {
        qDebug() << "QML element found...";
        context->setContextProperty("mapConnection", map);
    }

    return a.exec();

And the QML file:

import QtQuick 2.0
import QtQuick.Window 2.0
import QtLocation 5.6
import QtPositioning 5.6

Item {
    objectName: "mapItem"
    Plugin {
        id: osmPlugin
        objectName: "osmPlugin"
        name: "osm"
        PluginParameter {
                    name: "osm.mapping.providersrepository.disabled"
                    value: "true"
        }

        PluginParameter {
                    name: "osm.mapping.providersrepository.address"
                    value: "http://maps-redirect.qt.io/osm/5.6/"
        }
    }

    Map {
        objectName: "osmMap"
        anchors.fill: parent
        plugin: osmPlugin
        center: QtPositioning.coordinate(59.91, 10.75) // Oslo
        zoomLevel: 11
    }
}

SGaist

Hi,

You should rather do it the other way around. Emit a signal from your C++ object and connect to it in your QML code and update there whatever you want.

vmetodiev

Hi @SGaist ,
Alright, thanks a lot for the hint!

vmetodiev

Story continued here: https://forum.qt.io/topic/135852/binding-qquickwidget-to-qml-contex-inside-mainwindow