Strange behavior when adding SystemCommand to switch screen modes

[cdxjcl]

I tried adding a SystemCommand to switch from the Main Screen to the Setting Screen, following the guide. However, when I click the Header button or press Ctrl+P, the command palette does not open—instead, the Setting Screen switches immediately. On the second attempt to open the palette, the app crashes.

from typing import Iterable

from textual.app import App, ComposeResult, SystemCommand
from textual.screen import Screen
from textual.widgets import (
    Footer,
    Header,
    Placeholder,
)


class SettingScreen(Screen):
    BINDINGS = [("esc", "app.switch_mode('main')", "Exit")]

    def compose(self) -> ComposeResult:
        yield Header()
        yield Placeholder("Setting Screen")
        yield Footer()


class MainScreen(Screen):
    def compose(self) -> ComposeResult:
        yield Header()
        yield Placeholder("Main Screen")
        yield Footer()


class FooApp(App):
    BINDINGS = [
        ("q", "quit", "Quit"),
    ]

    MODES = {
        "main": MainScreen,
        "setting": SettingScreen,
    }

    async def on_mount(self) -> None:
        await self.switch_mode("main")

    def get_system_commands(self, screen: Screen) -> Iterable[SystemCommand]:
        yield from super().get_system_commands(screen)
        yield SystemCommand("Setting", "App Setting", self.switch_mode("setting"))


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

Crash Info:

DuplicateIds: Tried to insert a widget with ID '--command-palette', but a widget already exists with that ID (CommandPalette(id='--command-palette', classes='-ready
--textual-command-palette')); ensure all child widgets have a unique ID.

Textual Diagnostics

Versions

Name	Value
Textual	6.1.0
Rich	14.1.0

Python

Name	Value
Version	3.13.5
Implementation	CPython
Compiler	MSC v.1943 64 bit (AMD64)
Executable	C:\Users\xxx.venv\Scripts\python.exe

Operating System

Name	Value
System	Windows
Release	11
Version	10.0.26100

Terminal

Name	Value
Terminal Application	Windows Terminal
TERM	Not set
COLORTERM	Not set
FORCE_COLOR	Not set
NO_COLOR	Not set

Rich Console options

Name	Value
size	width=165, height=48
legacy_windows	False
min_width	1
max_width	165
is_terminal	True
encoding	utf-8
max_height	48
justify	None
overflow	None
no_wrap	False
highlight	None
markup	None
height	None

[github-actions[bot]]

We found the following entry in the FAQ which you may find helpful:

• Why do some key combinations never make it to my app?

Feel free to close this issue if you found an answer in the FAQ. Otherwise, please give us a little time to review.

This project is developed and maintained by Will McGugan. Consider sponsoring Will's work on this project (and others).

This is an automated reply, generated by FAQtory

[willmcgugan]

Have a look at the following line again:

yield SystemCommand("Setting", "App Setting", self.switch_mode("setting"))

The third argument expects a callback, but you are calling switch_mode. So the switch happens right there in that method.

What you want is to supply a callable so the command palette can call it when it is selected. In the examples you linked to, you will notice that the third parameter is self.bell, and not self.bell().

Given that your callback has a parameter, you could replace the call with a partial or a lambda. Or define a new method. For example:

def switch_settings_mode(self):
    self.switch_mode("setting")

yield SystemCommand("Setting", "App Setting", self.switch_settings_mode)

[cdxjcl]

Thank you so much — I just realized this was my own oversight.
Really appreciate your help!