ubuntu-phone team mailing list archive

[Andrea Bernabei <andrea.bernabei@xxxxxxxxxxxxx>]

On Mon, Apr 18, 2016 at 12:43 PM, Alberto Mardegan <
alberto.mardegan@xxxxxxxxxxxxx> wrote:

> On 18/04/2016 13:57, Omer Akram wrote:
> > While working on a pet project[1] for the Phone, an issue that I faced
> > was stuttering scrolling in listviews. QML tips page[2] suggested to use
> > Flickable+Column+Repeater combination to have smooth scrolling, that
> > worked and is currently what I have implemented in my app but I always
> > thought that was not the perfect solution.
> >
> > With some knowledge of how Android ListView works and its mechanism of
> > recycling ListView items, I wrote a hack[3] to achieve something similar
> > in QML.
> [...]
>
> You are trying to reinvent the QML ListView :-)
> The QML ListView recycles the delegates, and this behaviour is partially
> configurable via the cacheBuffer property:
>
>   http://doc.qt.io/qt-5/qml-qtquick-listview.html#cacheBuffer-prop
>
> Now, this means that when scrolling a listview, occasionally the
> delegates need to be either created (the first time they are used) or
> reused (which causes a reassignment of their properties based on the
> model data).
> Both these operations can be expensive, that's why someone gave the tip
> of using a Column+Repeater when the number of delegates is low and
> doesn't change, so that the whole list is created only once and
> scrolling will be smooth.
>
> If now you found that this tip doesn't work well for you (typically
> because of high memory consumption if the model has many items), it
> means that you should go back to using a ListView. :-)
>
>
Does ListView reuse delegates?
As far as I know, it creates new ones on the fly, every time.

I guess Omar's solution was for cases where:
- you have fixed delegate height
- you have a fixed and known number of delegates
- you want to avoid instantiating all of them at once

in that case reusing the delegates could work better than recreating them
like ListView does.

If I'm wrong and ListView already reuses delegates instances, then my
points above are of course void.


> Ciao,
>   Alberto
>
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