Plasma 2 DataEngine & QML bindings

[Sebastian Kügler]

Hi Mark,

On Wednesday, July 03, 2013 11:41:20 Mark wrote:
> On Tue, Jul 2, 2013 at 3:18 AM, Sebastian Kügler <sebas at kde.org> wrote:

> > I'm looking into our dataengine and relevant QML bindings right now, I can
> > now load a dataengine and use it from Plasma 2, but I have to convert the
> > payload (::data() from a QHash to a QVariantMap.
> > 
> > In src/declarativeimports/core/datasource.*) the data property returns
> > QHash<QString, QVariant>. This doesn't seem to be consumable from QML,
> > (javascript code sees a  QVariant(QVariantHash), but I can't iterate over
> > it, it has no keys, no [] accessors, etc..
> > Converting it to a QVariantMap instead makes it work from QML, but it's
> > not
> > actually what we want to do here. Or is it?
> > 
> > There's some qscriptvalue magic that I don't understand completely in
> > dataenginebindings_p.h, is this the necessary glue to do the conversion
> > automatically (and more efficiently)?

> Just a quick thought. Does it help if you expose the data as a
> QAbstractItemModel (or QAbstractListModel)? That way you stay in
> control of how the data is represented in the backend without
> conversions specifically for QML. It also makes it very easy to use
> the data in QML views
> 
> The downside is probably that you need to have a model class which can
> be a big pain to make (specially QAbstractItemModel).

We actually have that, and you're correct: it's a pain. That's mainly because 
you have to set the rolenames pretty early on, otherwise the data is not 
visible from QML, and it took us a lot of fixing. I haven't tested this code 
path in PW2 though.
That's in declarativeimports/core/datamodel.cpp

For the simple case, where the dataengine just passes through a smallish set 
of data, it works now (with QVariantHash), and I've actually already moved on.

I want to change as little code as possible in there, since it's quite brittle 
and could incur some serious porting costs for everybody.

Btw, didn't you write a calendarcomponent which we could use in the QML 
version of the clock? :)

Cheers,
-- 
sebas

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