Dear Ulf,
On Thu, Jun 23, 2022, at 23:21, Ulf Hermann wrote:
> In Qt5 if we have a QQmlEngine, each and every Qt namespace enum value
> is added as a property to the Qt object, keyed by a newly created
> QString, wrapped into a JS string, and the whole thing every time you
> query one of those enums (until you query something that doesn't exist).
> You may guess why I've removed this particular piece of code.
I fully understand why it would be desirable to remove such a kludge, though I
might have expected a bit more consideration for applications that relied on
these values. But maybe my use-case is pretty rare. Thanks a lot for your
elaborate explanation and the suggested workarounds!
> If you want to work around the problem, there are a number of ways to
> extend the JavaScript environment. For example:
>
> QJSEngine engine;
> engine.installExtensions(QJSEngine::AllExtensions);
> engine.globalObject().setProperty(
> QStringLiteral("QtNamespace"),
> engine.newQMetaObject(&Qt::staticMetaObject));
> engine.evaluate(QStringLiteral("console.log(QtNamespace.Checked)"));
That worked, thanks! However, for compatibility I really need both the
functions and the enums, so I also tried the neat trick:
> QJSEngine engine;
> engine.installExtensions(QJSEngine::AllExtensions);
> QJSValue qtObject = engine.globalObject().property("Qt");
> QJSValue qtNamespace = engine.newQMetaObject(&Qt::staticMetaObject);
> qtNamespace.setPrototype(qtObject);
> engine.globalObject().setProperty("Qt", qtNamespace);
> engine.evaluate(QStringLiteral("console.log(Qt.Checked)"));
This is very promising, but unfortunately I could only get it to work with
QJSEngine and not with QQmlEngine. With the latter, the Qt object stubbornly
still only provides various functions.
I'm relying on QQmlEngine rather than a QJSEngine, because only the QQmlEngine
provides basic functions to control where output goes, like
QQmlEngine::setOutputWarningsToStandardError (which I use to disable this) and
the QQmlEngine::warnings signal (which I use to route any JS errors to a
Console window inside the application).
Would there be any way to get this working with a QQmlEngine?
Alternatively, I guess I could open a feature request for the errors/warnings
related API to be made available at the QJSEngine level. Though I would
eventually like to support loading QML extensions as well.
> Now, it wouldn't be all that hard to do the above prototype trick
> already when adding the Qt object to the JS global object. I need to
> check if it opens new compatibility pitfalls, though.
That'd be nice, and hopefully it would work for both QJSEngine and QQmlEngine.
But yeah, it's a bit hard to foresee the consequences.
Cheers,
Thorbjørn
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