OptionList with only one parameter does not return highlighted

[CognitiveDisson]

I subclassed OptionList, added an on_key callback, and noticed that if the list contains only one option, the highlighted property always None.
I subclassed OptionList, added an on_key callback, and noticed that if the list contains only one option, the highlighted property always None. (even when you select the row with that option and it's visually highlighted)

class ListWidget(OptionList):
    def on_mount(self) -> None:
        self.add_option(Option("1"))

    def on_key(self, event: events.Key) -> None:
        print(f"highlighted: {self.highlighted}")

In textual console:

highlighted: None

[davep]

I'd expect this behaviour, which doesn't have anything to do with just having one option. If you create an OptionList with no options, and then add more afterwards, nothing with be highlighted until some sort of input causes an option to be highlighted. As such highlighted should be None.

See this in action with this little app, which creates an OptionList with no options, adds some on_mount, logs highlighted, and then further logs highlighted when the highlight is moved.

from textual import on
from textual.app import App, ComposeResult
from textual.containers import Vertical
from textual.widgets import OptionList, TextLog
from textual.widgets.option_list import Option

class OptionListApp(App[None]):

    CSS = """
    OptionList {
        height: 4fr;
    }

    TextLog {
        height: 1fr;
    }
    """

    def compose(self) -> ComposeResult:
        with Vertical():
            yield OptionList()
            yield TextLog()

    def on_mount(self):
        for n in range(20):
            self.query_one(OptionList).add_option(Option(f"Here is option {n}"))
        self.log_highlighted()

    @on(OptionList.OptionHighlighted)
    def log_highlighted(self) -> None:
        highlighted = self.query_one(OptionList).highlighted
        self.query_one(TextLog).write(f"Highlighted: {highlighted!r}")

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

[nmay231]

I subclassed OptionList, added an on_key callback, and noticed that if the list contains only one option, the highlighted property always None. (even when you select the row with that option and it's visually highlighted)

@CognitiveDisson As already mentioned, if there is no option selected, it should print None. However, I got highlighted: 0 when I selected the row, so there must be something else going on for you to get None even after the row is selected.

[willmcgugan]

The issue was that the OptionList didn't have an opertunity to process the key bindings. Responding to the OptionList.OptionHighlighted event as @davep suggested will ensure that your code runs when the highlight changes.

This code reproduces the issue (and includes the solution).

from textual.app import App, ComposeResult
from textual.widgets import OptionList
from textual.widgets.option_list import Option
from textual import events
from textual import on


class ListWidget(OptionList):
    def on_mount(self) -> None:
        self.add_option(Option("1"))

    def on_key(self, event: events.Key) -> None:
        print(f"highlighted: {self.highlighted}")

    @on(OptionList.OptionHighlighted)
    def highlight_changed(self, event: OptionList.OptionHighlighted) -> None:
        print(f"highlighted (change): {self.highlighted}")


class TestApp(App):
    def compose(self) -> ComposeResult:
        yield ListWidget()


app = TestApp()
app.run()

[CognitiveDisson]

Thanks for helping solve that issue. The suggested solution works for me.