Qt Qml, embedding a map (OSM Mapbox Mapboxgl) into a QQuickWidget C++ object, on iOS

Question

I am developing a cross-platform mobile application which must display a geographical map. then we're using Qt framework (Qt 5.9), and the main part of the implementation is in C++.

Qt has ready-to-use Map objects available in QML. Then, the best way I found to integrate the map view is to load QML code into a QQuickWidget.

The following piece of code works fine on MacOS Desktop but I am still getting a blank view when deploying on iOS.

map.qml

import QtQuick 2.0
import QtQuick.Controls 1.4
import QtLocation 5.9
import QtPositioning 5.5

Map {
    id: map
    plugin: Plugin {
        name: "mapboxgl"
        PluginParameter { name: "mapboxgl.access_token"; value: "***" }
    }

    center: QtPositioning.coordinate(60.170448, 24.942046) // Helsinki
    zoomLevel: 8

    width: 500  // no effects since it will be resized
    height: 500 // no effects since it will be resized
    gesture.enabled: true

    Component.onCompleted: {
        console.log("Dimensions: ", width, height) // print 500 500 whether or not the map is displayed
    }
}

viewport.cpp

Viewport::Viewport(QWidget *parent) : QWidget(parent),
    _engine(new QQmlEngine(this)),
    _mapview(new QQuickWidget(_engine,this)),
    _toolbar(new Toolbar(this)) // subclass of QWidget
{
    _mapview->setSource(QUrl("qrc:/map.qml"));
    _mapview->setResizeMode(QQuickWidget::SizeRootObjectToView);
}

Note :

map.qml is properly declared at the root of a qt resource file, so that mobile device can access it. I know mapboxgl plugin is very new on Qt 5.9 No matter what plugin I use for the map (osm, mapbox, mapboxgl) I'm always getting a blank view on iOS, with no error message.
When running a simple sample project, the warning message for mapboxgl plugin is something like ssl handshake failed. Even though Qt says the mapboxgl QML plugin, for instance, supports iOS.
The Viewport class inherits from QWidget and is not associated to any ui file, both of the _mapview and the _toolbar geometries are managed by hand. For the moment there is no overlapping widgets and all of them are fully opaque. Nevertheless I tried to set/unset several OpenGL attributes (Qt::AA_UseOpenGLES, Qt::AA_ShareOpenGLContexts etc...) but still don't do the thing ...
Last note : replacing the map of the above code, with a simple red Rectangle with a Text on it works well.

My question what am I doing wrong ? Did I miss something in the documentation ? Nothing says iOS cannot support these map qml objects.

fury fury · Accepted Answer · 2017-07-08T00:53:12

It looks as though this is due to a bug in Qt 5.9.0's SSL socket handling for iOS - https://bugreports.qt.io/browse/QTBUG-61053

I was seeing in the debug output "SSL handshake failed" when attempting either with osm highdpi tiles, or with mapboxgl.

I opened the online installer, added Qt 5.9.1 iOS, waited a bit while it downloaded, then reconfigured the project for 5.9.1 iOS and it worked.

Qt Qml, embedding a map (OSM Mapbox Mapboxgl) into a QQuickWidget C++ object, on iOS

1 Answers