The moment of setting the focus has changed (omits can_focus set in on_mount) after the 2.0.0

[mzebrak]

This works correctly in 1.0.0 but changed in 2.0.0.

Right after launch, Long widget should have focus (so, e.g. key_down binding should work and scroll). But it is not focused since 2.0.0.

CanFocusOnlyWhenScrollbars originated from: #3717

MRE:

from __future__ import annotations

from textual.app import App, ComposeResult
from textual.containers import VerticalScroll
from textual.widget import Widget
from textual.widgets import Static


class CanFocusWithScrollbarsOnly(Widget):
    """
    A Widget that can be focused only when scrollbar is active.

    Inherit from this class to make a widget focusable only when any scrollbar is active.
    """

    def on_mount(self) -> None:
        self._enable_focus_only_when_scrollbar_is_active()

    def watch_show_vertical_scrollbar(self) -> None:
        self._enable_focus_only_when_scrollbar_is_active()

    def watch_show_horizontal_scrollbar(self) -> None:
        self._enable_focus_only_when_scrollbar_is_active()

    def _enable_focus_only_when_scrollbar_is_active(self) -> None:
        self.can_focus = any(self.scrollbars_enabled)


class Long(VerticalScroll, CanFocusWithScrollbarsOnly):
    """Will be focused right after launching  in 1.0.0 but not in 2.0.0."""

    def compose(self) -> ComposeResult:
        for i in range(50):
            yield Static(f"static no. {i}")


class MyApp(App):
    def compose(self) -> ComposeResult:
        yield Long()


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

[willmcgugan]

from __future__ import annotations

from textual.app import App, ComposeResult
from textual.containers import VerticalScroll
from textual.widget import Widget
from textual.widgets import Static


class Long(VerticalScroll):
    """Will be focused right after launching  in 1.0.0 but not in 2.0.0."""

    def allow_focus(self) -> bool:
        return any(self.scrollbars_enabled)

    def compose(self) -> ComposeResult:
        for i in range(50):
            yield Static(f"static no. {i}")


class MyApp(App):
    def compose(self) -> ComposeResult:
        yield Long()

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[TomJGooding]

I almost raised an issue about allow_focus earlier, as I don't think it works as expected.

Here's a slightly modified version of your example. When you first start the app, this widget is still focusable despite not having any scrollbars:

from __future__ import annotations

from textual.app import App, ComposeResult
from textual.containers import VerticalScroll
from textual.widget import Widget
from textual.widgets import Button, Static


class Long(VerticalScroll):
    DEFAULT_CSS = """
    Long {
        border: tall red;
        &:focus {
            border: tall green;
        }
    }
    """

    def allow_focus(self) -> bool:
        return any(self.scrollbars_enabled)

    def compose(self) -> ComposeResult:
        for i in range(10):
            yield Static(f"static no. {i}")


class MyApp(App):
    def compose(self) -> ComposeResult:
        yield Long()
        yield Button()


if __name__ == "__main__":
    app = MyApp()
    app.run()

[mzebrak]

Adding basic logging to the allow_focus method shows that it is not called when the widget is mounted. So initially Widget does have focus even though allow_focus would return False.

from __future__ import annotations

from textual.app import App, ComposeResult
from textual.containers import VerticalScroll
from textual.widget import Widget
from textual.widgets import Button, Static


class Long(VerticalScroll):
    DEFAULT_CSS = """
    Long {
        border: tall red;
        &:focus {
            border: tall green;
        }
    }
    """

    def allow_focus(self) -> bool:
        v = any(self.scrollbars_enabled)
        self.log(f"allow_focus value:: {v}")
        return v

    def compose(self) -> ComposeResult:
        for i in range(10):
            yield Static(f"static no. {i}")


class MyApp(App):
    def compose(self) -> ComposeResult:
        yield Long()
        yield Button()


if __name__ == "__main__":
    app = MyApp()
    app.run()