Wednesday, 18 February 2015

RE: [Ubuntu-phone] Qt 5.4 QVariant change and module news

Hi!

I have just received a vivid-proposed image and noticed that U1db no longer loads the defaults (which was probably a processed QVariantMap from JS). Did this change break it/could it break even more components?

> Date: Tue, 17 Feb 2015 09:37:38 +0200
> From: [email protected]
> To: [email protected]
> CC: [email protected]
> Subject: [Ubuntu-phone] Qt 5.4 QVariant change and module news
>
> Qt 5.4 is now in vivid, powering Ubuntu Phone starting with devel
> image #102, Kubuntu's Plasma 5 and also the Unity 8 desktop preview.
> No app changes are generally needed, but there is a change in QVariant
> that may be relevant to C++ using apps.
>
> == QVariant change in Qt 5.4 ==
>
> QVariant has changed a bit in Qt 5.4, although in a way that fixing
> its use does not affect negatively use in Qt 5.3 either.
>
> Quote: "When a JavaScript object/array is passed to C++ through a
> QVariant, the engine no longer immediately converts the object
> recursively into a QVariantMap or QVariantList but instead stores a
> QJSValue in the QVariant. This prevents a loss of data when the JS
> object contains non-primitive types such as function objects for
> example. Code that expects the variant type to be exactly
> QVariant::Map or QVariant::List may need to be adapted. Registered
> conversion functions however ensure that code that merely calls
> toMap() or toList() continues to work." [QTBUG-40431]
>
> Examples of fixes:
> - Oxide: https://code.launchpad.net/~aacid/oxide/qt54_variantjs/+merge/248765
> - Ubuntu UI Toolkit:
> https://code.launchpad.net/~aacid/ubuntu-ui-toolkit/statesaver_54/+merge/247986
>
> Another noted small difference:
> "In Qt 5.4 an alias to a null variable is correctly null instead of
> undefined like it was in Qt 5.3"
>
> == Status of less supported Qt modules ==
>
> It's useful to remember that not all of Qt we have in Ubuntu is
> supported by the Qt Project:
>
> - qtlocation: Upstream releases this as part of their releases, but
> they emphasize that Qt Positioning is API stable while Qt Location
> might change. Still, this should be pretty safe to use and will
> probably be declared stable soon.
> - qt3d: The original module has not been developed for two years. A
> complete rewrite has been in development during that time. Qt 3D 2.0
> will be available as a preview with Qt 5.5.
> - qtsystems: Semi-active development. Qt 5.4 absorbed QStorageInfo to
> be official part of qtbase, but it is a bit different and oddly does
> not have QML support at this point. We include the SystemInfo module
> on the phone images, but currently not the Publish Subscribe or
> Service Framework modules from the same source.
> - qtpim: Semi-active development, but can be considered supported
> since our Renato is one of the upstream developers. Ubuntu uses the
> Contacts/Organizer extensively in phone/scheduling apps.
> - qtfeedback: Stable in the sense that there is no development
> happening. It's also a very small module. If you are interested in the
> module, consider taking an active role in the Qt Project where
> contributions would surely be welcome.
>
> -Timo
>
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