Setting OptionList.highlighted after repopulating with new options doesn't update the vertical scrollbar

[davep]

This might be a variation of #5631, but the workaround I used there doesn't seem to work here so I thought it worth writing up as a separate MRE of a possibly-different effect.

Given this code:

from textual.app import App, ComposeResult
from textual.widgets import OptionList

class OptionListScrollIssueApp(App[None]):

    CSS = """
    OptionList {
        height: 1fr;
    }
    """

    BINDINGS = [("space", "toggle_size")]

    def compose(self) -> ComposeResult:
        yield OptionList(*[f"This is option {n}" for n in range(1000)])

    def on_mount(self) -> None:
        # Workaround for https://github.com/Textualize/textual/issues/5631
        self.call_after_refresh(self.query_one(OptionList).action_last)

    def action_toggle_size(self) -> None:
        option_list = self.query_one(OptionList)
        new_conent = [f"This is option {n}" for n in range(5 if option_list.option_count == 1000 else 1000)]
        option_list.clear_options().add_options(new_conent)
        option_list.highlighted = 0

if __name__ == "__main__":
    OptionListScrollIssueApp().run()

when you first run it you see this:

That is: the list is populated, the highlight is on the last item, the vertical scrollbar is in the correct place.

If you then press space you see this:

Again: all good; the list is repopulated and there is no vertical scrollbar visible.

If you press space again you see this:

Here the list is repopulated with lots of items, the highlight is on the first item (as intended), but the vertical scrollbar is positioned as if we were on the last item.

Even doing some form of call_after_refresh to reset the highlight doesn't seem to help. I can get the effect I would expect by tearing down and recreating the OptionList, of course:

from textual.app import App, ComposeResult
from textual.widgets import OptionList

class OptionListScrollIssueApp(App[None]):

    CSS = """
    OptionList {
        height: 1fr;
    }
    """

    BINDINGS = [("space", "toggle_size")]

    def compose(self) -> ComposeResult:
        yield OptionList(*[f"This is option {n}" for n in range(1000)])

    def on_mount(self) -> None:
        # Workaround for https://github.com/Textualize/textual/issues/5631
        self.call_after_refresh(self.query_one(OptionList).action_last)

    async def action_toggle_size(self) -> None:
        next_size = 5 if self.query_one(OptionList).option_count == 1000 else 1000
        with self.batch_update():
            await self.query_one(OptionList).remove()
            await self.mount(OptionList(*[f"This is option {n}" for n in range(next_size)]))
            self.query_one(OptionList).focus()

if __name__ == "__main__":
    OptionListScrollIssueApp().run()

Textual Diagnostics

Versions

Name	Value
Textual	2.1.2
Rich	13.9.4

Python

Name	Value
Version	3.13.1
Implementation	CPython
Compiler	Clang 18.1.8
Executable	/Users/davep/temp/z/.venv/bin/python3

Operating System

Name	Value
System	Darwin
Release	24.3.0
Version	Darwin Kernel Version 24.3.0: Thu Jan 2 20:23:36 PST 2025; root:xnu-11215.81.4~3/RELEASE_ARM64_T8112

Terminal

Name	Value
Terminal Application	ghostty (1.1.2)
TERM	xterm-256color
COLORTERM	truecolor
FORCE_COLOR	Not set
NO_COLOR	Not set

Rich Console options

Name	Value
size	width=114, height=56
legacy_windows	False
min_width	1
max_width	114
is_terminal	False
encoding	utf-8
max_height	56
justify	None
overflow	None
no_wrap	False
highlight	None
markup	None
height	None