scroll_end off by one

[aaronst]

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.

[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.

[aaronst]

Thanks @lxnn, you're right. Static.update is another one - I guess any method that could affect the dimensions?

[rstomallen]

await asyncio.sleep(0)
didn't work for me but
await asyncio.sleep(0.01)
did....

[willmcgugan]

Does the following fix it?

self.call_later(self.table.scroll_end)

[rstomallen]

self.console_outputs.append(json.dumps(results, indent=4)) self.query_one("#code", Static).update(self.console_outputs) self.call_later(self.body.scroll_end(animate=False, duration=0.01, easing="linear")) no 🙁

…

________________________________ From: Will McGugan ***@***.***> Sent: Tuesday, December 6, 2022 2:50 AM To: Textualize/textual ***@***.***> Cc: Tom Allen ***@***.***>; Comment ***@***.***> Subject: [EXTERNAL]Re: [Textualize/textual] scroll_end off by one (Issue #1215) Does the following fix it? self.call_later(self.table.scroll_end) — Reply to this email directly, view it on GitHub<#1215 (comment)>, or unsubscribe<https://github.com/notifications/unsubscribe-auth/AVAFQFVA7BTAZ34DZFGD5WLWL3V4FANCNFSM6AAAAAASEAMEUU>. You are receiving this because you commented.Message ID: ***@***.***>

[davep]

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 Will is passing the function scroll_end to call_later. call_later takes a callback function.

Try it how Will wrote it.

[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_later<https://textual.textualize.io/api/message_pump/#textual.message_pump.MessagePump.call_later> takes a callback function. Try it how Will wrote it. — Reply to this email directly, view it on GitHub<#1215 (comment)>, or unsubscribe<https://github.com/notifications/unsubscribe-auth/AVAFQFTZ6IQOBSD4YE6AZ2LWL5CLDANCNFSM6AAAAAASEAMEUU>. You are receiving this because you commented.Message ID: ***@***.***>

[keathmilligan]

I ran into this as well. Here was my hacky work-around:

        log_message = Label(str(message))
        await activity_log.mount(log_message)
        activity_log.scroll_end()
        activity_log.scroll_down()

I tried other combinations of call_later or setting a short timer, but this was the only way I could get the container to immediately scroll to the bottom. Most other attempts would initially result in the container scrolling to the next-to-the-last row and then about 100-200ms later the container would "correct" itself and scroll to the actual bottom.

[davep]

I suspect that #1902 will have helped here.

[rodrigogiraoserrao]

I suspect that #1902 will have helped here.

I believe so, too.
The original code works without any changes (i.e., calling self.table.scroll_end directly) as does the alternative solution with self.call_later(self.table.scroll_end), so I am closing this issue.

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