[Development] Qml/JS QVariantMap conversion problem

[Nils Jeisecke]

Hi Simon,

thank you very much for the explanation. No need for bug hunting then.

On Thu, Sep 25, 2014 at 7:55 AM, Simon Hausmann
<simon.hausmann at digia.com> wrote:
> We've changed this in Qt 5.4 slightly: When
> converting a JavaScript object back to a QVariant, we won't try to "destroy"
> it but instead we'll give you a QVariant that holds a (strong) reference to
> the JavaScript object, it'll be a QJSValue in a QVariant. Note how somebody
> could call setMap with the return value of buildMap() but also with a JS
> object literal: setMap( { x: ["a", "b" ] })
>
>     QVariant(QVariantMap, QMap(("x", QVariant(QStringList, ("a", "b")) ) ) )
>
> You can do the conversion like this:
>
>     QVariant map = ...
>     if (map.userType() == qMetaTypeId<QJSValue>())
>         map = qvariant_cast<QJSValue>(map).toVariant();
I think this should be added to the documentation. Maybe here:
http://doc-snapshot.qt-project.org/qt5-5.4/qtqml-cppintegration-data.html.
I'd give it a try if this is the right place.

This is very important to know especially if you use Qml only as glue
to directly bind C++ objects properties. I wasn't aware that this also
involves two (in this use case unwanted) conversions (C++ -> JS ->
C++).

Nils