Updating current screen before push_screen?

[TomJGooding]

Here's a minimal reproduction where a "Login successful!" message should be displayed before moving to the next screen. If you uncomment the push_screen line, the message no longer displays.

I'm guessing this has something to do with concurrency in Textual, but not sure how to approach a possible workaround?

Thanks in advance for any advice.

import time

from textual.app import App, ComposeResult
from textual.containers import Container
from textual.screen import Screen
from textual.widgets import Input, Label

PASSWORD = "textual"


class LoginScreen(Screen):
    def compose(self) -> ComposeResult:
        yield Container(
            Input(placeholder="Password"),
            Label(" "),
        )

    def on_mount(self) -> None:
        self.query_one(Input).focus()

    def on_input_submitted(self, event: Input.Submitted) -> None:
        password: str = event.input.value.strip()
        msg = self.query_one(Label)
        if password == PASSWORD:
            msg.update("Login successful! Loading...")
            # self.app.push_screen("main")
        else:
            msg.update("Incorrect password!")


class MainScreen(Screen):
    def on_mount(self) -> None:
        time.sleep(3)

    def compose(self) -> ComposeResult:
        yield Label("Hello World!")


class ExampleApp(App):
    CSS = (
        "Screen { align: center middle; }"
        "Container { align: center middle; max-width: 100; }"
    )
    SCREENS = {
        "login": LoginScreen,
        "main": MainScreen,
    }

    def on_mount(self) -> None:
        self.push_screen("login")


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

[davep]

Rather than just push the screen right away, I'd do this (assuming from functools import partial):

msg.call_after_refresh(partial(self.app.push_screen,"main"))

In other words: once the label has fully updated, then swap to the main screen.

[TomJGooding]

Thanks as always Dave! I wasn't aware of call_after_refresh... would you mind explaining what wrapping inside partial is doing here?

[davep]

So call_after_refresh takes a callable to call after the refresh happens, but push_screen has a parameter so we can't just pass a reference to the method alone, so I use it to make a partial that can be called later along with its parameter.

I could have written it like:

msg.call_after_refresh(lambda: self.app.push_screen("main"))

but I generally find Python's lambda ugly. ;-)

[davep]

@willmcgugan just reminded me that call_after_refresh can handle this, so this would work:

msg.call_after_refresh(self.app.push_screen,"main")

I forgot that it takes the arguments and makes the partial for you.

[TomJGooding]

Thank you both for your help!