Behavior of mount in new version

[vpet98]

After installing a newer version of textual, I notice a different behavior when mounting widgets to other widgets.

In the code provided below when the button is pressed I get NoMatches error, although lines widget is previously mounted (being inside a ContentSwitcher widget) in another widget.

import textual
from textual.app import App, ComposeResult
from textual.containers import Container, ScrollableContainer
from textual.widgets import Static, Button, ContentSwitcher


class Results(Static):
    def compose(self) -> ComposeResult:
        yield Static("Results")


class Test(App):
    def compose(self) -> ComposeResult:
        yield Results(id="results-widget")
        yield Button("Press")

    def on_button_pressed(self, event: Button.Pressed) -> None:
        self.query_one('#results-widget').mount(ContentSwitcher(Container(id="lines"), ScrollableContainer(Static(id="plain"), id="plain-container"), initial="lines", id='switcher'))
        item = self.query_one('#lines')

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

However, the below code works:

import textual
from textual.app import App, ComposeResult
from textual.containers import Container, ScrollableContainer
from textual.widgets import Static, Button, ContentSwitcher


class Results(Static):
    def compose(self) -> ComposeResult:
        yield Static("Results")
        yield ContentSwitcher(Container(id="lines"), ScrollableContainer(Static(id="plain"), id="plain-container"), initial="lines", id='switcher')


class Test(App):
    def compose(self) -> ComposeResult:
        yield Results(id="results-widget")
        yield Button("Press")

    def on_button_pressed(self, event: Button.Pressed) -> None:
        item = self.query_one('#lines')

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

I would expect both pieces of code to have the exact same behavior, as was the case a few versions of textual before (0.42.0 or 0.45.0 if I remember correctly)

[davep]

In your first example, you'd need to await the mount before you could query back the widgets:

--- vpet98.py-orig	2024-02-05 12:01:59
+++ vpet98.py	2024-02-05 12:02:05
@@ -14,8 +14,8 @@
         yield Results(id="results-widget")
         yield Button("Press")
 
-    def on_button_pressed(self, event: Button.Pressed) -> None:
-        self.query_one('#results-widget').mount(ContentSwitcher(Container(id="lines"), ScrollableContainer(Static(id="plain"), id="plain-container"), initial="lines", id='switcher'))
+    async def on_button_pressed(self, event: Button.Pressed) -> None:
+        await self.query_one('#results-widget').mount(ContentSwitcher(Container(id="lines"), ScrollableContainer(Static(id="plain"), id="plain-container"), initial="lines", id='switcher'))
         item = self.query_one('#lines')
 
 if __name__ == "__main__":