scroll_end off by one

It looks like Widget.scroll_end() is off by one line. Here’s an app to reproduce:

from textual.app import App, ComposeResult
from textual.widgets import DataTable, Footer


class Test(App):
    BINDINGS = [("a", "add_row", "Add a row")]
    DEFAULT_CSS = """
    DataTable {
        height: 5;
    }
    """

    def compose(self) -> ComposeResult:
        rows = (
            ("1", "one"),
            ("2", "two"),
            ("3", "three"),
            ("4", "four"),
            ("5", "five"),
        )

        self.table = DataTable()
        self.table.add_columns("#", "number")
        self.table.add_rows(rows)

        yield self.table
        yield Footer()

    def action_add_row(self) -> None:
        self.table.add_row("6", "six")
        self.table.scroll_end()


Test().run()

After adding the sixth row, the DataTable scrolls to the fifth row.

[rstomallen]

Ah, thanks for the explanation, I changed it, thanks. Yes, it does work, albeit slowly. My end use case is a MUD/telnet client which will scroll a lot more lines, faster. I’ll play around with using the call_later callback.

Thanks again!

tom

---

From: Dave Pearson @.> Sent: Tuesday, December 6, 2022 9:09 AM To: Textualize/textual @.> Cc: Tom Allen @.>; Comment @.> Subject: [EXTERNAL]Re: [Textualize/textual] scroll_end off by one (Issue #1215)

self.call_later(self.body.scroll_end(animate=False, duration=0.01, easing=“linear”))

Note that what you’ve done there isn’t the same as what will suggested though. You’re passing the result of scroll_end to call_later, whereas well is passing the function scroll_end to call_later. call_laterhttps://textual.textualize.io/api/message_pump/#textual.message_pump.MessagePump.call_later takes a callback function.

Try it how Will wrote it.

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[lxnn]

Hello

I believe because action_add_row() is synchronous, the relevant dimensions won’t have been updated by the time scroll_end() is called.

(Details: add_row() does some stuff then calls check_idle(), sending out a message which is eventually handled by DataTable.on_idle(), where the dimensions are updated.)

I’m not sure if there’s a simple way to guarantee the behavior you want, but the following worked the few times I tested it:

    async def action_add_row(self) -> None:
        self.table.add_row("6", "six")
        await asyncio.sleep(0)
        self.table.scroll_end()

Some other methods, such as Widget.mount(), return an awaitable. It could be useful if DataTable.add_row() did too.