Move cursor after adding rows

[willmcgugan]

Reported on Discord. If you add rows then call move cursor, the view won't follow the cursor.

A workaround is to use call_after_refresh, which suggests something on idle needs to be done before move_cursor works?

from textual.app import App
from textual.widgets import DataTable


class TestMove(App):
    def compose(self):
        yield DataTable()

    def on_mount(self):
        dt = self.query_one(DataTable)
        dt.add_column("thecolumn")

        for row in range(1000):
            dt.add_row(f"row number {row}")

        dt.move_cursor(row=500, column=1, animate=True)
        # self.call_after_refresh(dt.move_cursor, row=500, column=1, animate=False)


TestMove().run()

[TomJGooding]

I think similar to #3533, the problem is that DataTable dimensions are only calculated on idle. The window in scroll_to_region has a height/width of zero, so the scrolling with move_cursor won't work.

But I'm sure you figured that out already, I'm just not sure of the proper fix.

[darrenburns]

Yeah, exactly right. The virtual_size needs to be updated before move_cursor works. Since the virtual_size is recomputed inside on_idle, if you try to move the cursor immediately, it won't work.

I think the fix is literally just to use call_after_refresh(self._scroll_cursor_into_view) inside move_cursor, since this can only work after on_idle runs.

I've implemented this fix in #3552

[TomJGooding]

Both fixes a lot more straightforward then I expected!

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