QML WebChannel - "value updates in HTML will be broken"

Stuart Jones

After a bit of work, I've got WebChannel working from my QML:

import QtQuick 2.7
import QtQuick.Window 2.2
import MyLibrary 1.0

Window {
    width: 1280
    minimumWidth: 1024

    height: 960
    minimumHeight: 240

    WebEngineView {
        webChannel: myWebChannel

        anchors.fill: parent
    }

    WebChannel {
        id: myWebChannel
        registeredObjects: [myLibraryObject]
    }

    MyLibraryObject {
        id: myLibraryObject
        WebChannel.id: "myLibaryObject"
    }
}

The HTML:

<head>
    <script type="text/javascript" src="qrc:///qtwebchannel/qwebchannel.js"></script>
    <script type="text/javascript" src="qrc:///js/modules/myLibrary.js"></script>
</head>

And the Javascript:

console.log("myLibrary.js");

window.onload = function() {
    new QWebChannel(qt.webChannelTransport, function (channel) {
        var myLibraryObject = channel.objects.myLibraryObject;

        console.log(myLibraryObject.label);
    });
}

When I run my application, the debug output is full of "Property 'X' of object 'QQuickItem' has no notify signal and is not constant, value updates in HTML will be broken!"

It refers not only to my custom MyLibraryObject, but also QQuick objects lik QQuickItem and QQuickRectangle.

I'm also seeing a number of "Don't know how to handle '', use qRegisterMetaType to register it."

How is this all fixed?