[Interest] QML: Use singleton types instead of pragma library scripts

Dmitry Q linuxsquirrel.dev at gmail.com
Fri Dec 26 12:43:17 CET 2014

Thanks, now it is clear what did they mean

2014-12-26 13:22 GMT+03:00 Dmitry Volosnykh <dmitry.volosnykh at gmail.com>:

> Dmitry, you can read more on that in this wiki article:
> http://qt-project.org/wiki/QmlStyling
> Primarily, you are interested in section "Nesting QtObjects", but reading
> the whole article would be useful too.
> In our application, we found it more convenient to do that in slightly
> different manner. We instantiate a single instance of that component
> (rather than making it be a true singleton) which is placed in the root
> .qml file and provided with some id (say, 'appStyle') which is supposed by
> our internal convention to be a global name used to refer from any other
> QML component. This trick allows us to live code UI components. True
> singletons lack this ability since they are not re-created at the time UI
> gets reloaded due to changes to .qml files. My collegue has noted that such
> implicit referring to an id out of component definition may impact QML
> engine performance. Maybe some one can elaborate more on this.
> Regards,
> Dmitry.
> On Fri, Dec 26, 2014 at 1:12 PM, Dmitry Q <linuxsquirrel.dev at gmail.com>
> wrote:
>> Hi. In the official QML documentation we see the following suggestion (
>> http://doc.qt.io/qt-5/qtquick-performance.html):
>> >>>
>> Use singleton types instead of pragma library scripts
>> If you are using a pragma library script to store application-wide
>> instance data, consider using a QObject singleton type instead. This should
>> result in better performance, and will result in less JavaScript heap
>> memory being used.
>> <<<
>> What does is mean? How should we use QObject singletons? For example, I
>> have the following ".pragma library" JS to store application-wide constants:
>> .pragma library
>> var X = 10;
>> ... many other declarations...
>> How should I rewrite this with QObject singletons?
>> _______________________________________________
>> Interest mailing list
>> Interest at qt-project.org
>> http://lists.qt-project.org/mailman/listinfo/interest
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