How to implement (and use) custom themes for std-widgets.slint?

[Reverier-Xu]

Hi, I'm trying to use slint to develop application with my own design.

In Qt/QML, we could change the outlook of QtQuick Controls by deriving QtQuick.Templates, then provide a style plugin as a library, I have developed a set of styled controls in my media player, and I want to do the same thing to styling std-widgets.slint in slint, but it seems do not have similar features like QtQuick.Templates?

I also tried write my widgets from scratch using basic elements, but I found ListView has "Elements are only instantiated if they are visible", which I can't find the implementation in the source code of listview.slint. Although I can implement the display optimizations myself, I still want to simply styling std-widgets.slint or reuse logic infrastructures instead of re-implement wheels.

Is there some way to implement themes like fluent or cosmic without monkey-editing slint's source code?

[Reverier-Xu]

Additional: ListView in QtQuick is provided as a basic element, not a styled-control.

Maybe we could do the same thing? provide something like ListView as a basic element and styling & extending it as another name in std-widgets.slint.

[ogoffart]

Is there some way to implement themes like fluent or cosmic without monkey-editing slint's source code?

The way this was designed is that one would adapt the include path so that "std-widgets.slint" point to your own.
But in practice this is hardly possible because the styles now rely on some internal that might not even be accessible.
This is tracking in issue #45 , but we are currently not really working on that.

Regarding the ListView question, the ListView has special handling in the compiler so that at runtime, a special layout function is called:

slint/internal/core/model.rs

Line 959 in 87702e9

pub fn ensure_updated_listview(

This works by just matching the name of the component to "ListView", so if you declare a component called ListView, it will have the same behavior (#861)