ubuntu-phone team mailing list archive

[Omer Akram <omer.akram@xxxxxxxxxxxxx>]

On Mon, Apr 18, 2016 at 4:43 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


My initial implementation was indeed using ListView and with a
higher(random) cacheBuffer, it was smooth but I had that itch of
experimenting and producing an optimized version of ListView. Plus I have
seen quite a few apps in the store have scrolling issues.

>
>
> 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.
>

Well, I think re-using already created elements and updating their
properties is potentially much less resource hungry than creating a new
element, though I don't have stats to prove that but my experimental
ListView scrolls smooth, as I would expect it to.


>
> 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. :-)
>
> Ciao,
>   Alberto
>
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