Fabulous: Improve performance when item is prepended to list

[johannesegger]

Elm solves this using keyed nodes, React using key attributes, but I didn't find anything similar in Fabulous. Did I miss something or is it not implemented yet?

[davidglassborow]

No you are correct, nothing like this has been implemented.

Please see performance notes on current approaches to optimising performance - Currently list views are optimised for appending rather than prepending.

We accept PRs though if it something you need and fancy having a go at it 😄

[johannesegger]

The alternative is to play around with Layout.RaiseChild and Layout.LowerChild, but in an Elmish architecture that's something I don't really want to play around with.

I'll see if I have the time, energy and skills to put together a PR, thanks.

[dsyme]

I think adding an equivalent to key nodes is an important part of "completing the picture" for Fabulous and bringing it on-par with React and Elm

[TimLariviere]

With Fabulous and Fabulous.XamarinForms now separated, we will need to write a new framework agnostic view diffing algorithm.
It will lead to a lot of rewrite, we should take this chance to implement keyed nodes

[Happypig375]

For anyone looking for workarounds, using isVisible can achieve a partial effect.
Instead of:

View.StackLayout [
    if condition then
        View.BoxView Color.Aqua
    View.BoxView Color.Yellow
]

use

View.StackLayout [
    View.BoxView Color.Aqua |> isVisible condition
    View.BoxView Color.Yellow
]

So that the view will not be destroyed and recreated whenever condition changes.

[TimLariviere]

Closing. It is now available in 0.55 (still preview), albeit performance still need improvements before releasing it as stable.