QML and QQuickItem with QWidgets

webzoid

I'm trying to get the mapviewer QML example application up and running in a QWidgets application.

Having successfully got the osm plugin displaying inside a QWidget, I'm trying to set or get some simple properties of the QML map object.

Being very, very new to QML (i.e. adventures only begun yesterday), I'm now a little stuck.

My QML looks like this:

import QtQuick 2.0

import QtLocation 5.9
import QtPositioning 5.8

Rectangle {
    id: containter;
    width: parent.width
    height: parent.height

    property variant startPoint: QtPositioning.coordinate(53.5, -3.5)

    Plugin {
        id: osmPlugin
        name: "osm"
    }

    Map {
        id: map
        anchors.fill: parent
        plugin: osmPlugin
        zoomLevel: 10
    }

    MouseArea {
        id: ma
        property variant coordinate
        anchors.fill: parent
        onClicked: {
            coordinate = map.toCoordinate(Qt.point(mouse.x, mouse.y))
            map.center = coordinate
            map.update()
        }
    }

    function setCenter() {
        map.center = startPoint
        map.update()
    }

    Component.onCompleted: setCenter()
}

And the initialization of the QQuickView and other QWidgets in MainWindow.cpp looks like this:

m_view = new QQuickView();
QWidget *container = QWidget::createWindowContainer(m_view);

m_view->setSource(QUrl("qrc:/test.qml"));

// Get the root object
QQuickItem *rect = m_view->rootObject();

// Get the map
QQuickItem *map = rect->childItems().at(0);

// How do I set this property???
//QGeoCoordinate center(0.0, 0.0);
//map->setProperty("center", center);

ui->centralWidget->setLayout(new QGridLayout());
ui->centralWidget->layout()->addWidget(container);

So far, so good.

The problem now comes when I want to, say, move the center location of the map from my QWidgets application - maybe via a button press or a function. The Qt documentation seems to indicate that I can use the setProperty function to do this however:

QGeoCoordinate center(0.0, 0.0);
map->setProperty("center", center);

Produces an error because there is no conversion between QGeoCoordinate and QVariant.

A trick is being missed. Any help would be greatly received!

webzoid

Ok, so a bit more Googling has brought me to the following function:

QVariant::fromValue() which allows me to pass in a QGeoCoordinate into the setProperty function and this seems to work.

The next trick is property retrieval. As an example, the supportedMapTypes property in the Map object returns a list of MapTypes for the current plugin.

I can iterate through the supportedMapTypes list in QML:

for (var i = 0; i < map.supportedMapTypes.length; i++) {
    console.log(map.supportedMapTypes[i].name);
}

And then in my QWidgets application, if I try to get the property:

QList<QVariant> types = map->property("supportedMapTypes").toList();

types is just an empty list.

GrecKo

Why QQuickView + QWidget::createWindowContainer instead of just QQuickWidget ?

webzoid

@GrecKo This is indeed a very good question. My searching hadn't brought me across a QQuickWidget before.

I shall investigate. Thanks.

webzoid

Ok, so I've sub-classed a QQuickWidget and added an instance to the ui->centralWidget->layout(). I've left a non-subclassed QQuickWidget with the same QML source in the layout for comparison.

When I run the application, the non-subclassed QQuickWidget renders the QML perfectly but the sub-classed version shows nothing but a white canvas - nothing is showing.

ldanzinger

Agreed on using QQuickWidget instead. As a side note, if you want a mapping API that supports Widgets (and thus won't require you to use classes like this to shoehorn a QML view into a Widgets app), you can check out the ArcGIS Runtime SDK for Qt - https://developers.arcgis.com/qt/