textual._on.OnDecoratorError: The message class must have a 'control' to match with the on decorator

[machin3io]

Using the Enter or Leave event decorators with a CSS selector throws the following exception:

Traceback (most recent call last):
  File "/home/x/Archive/python/2024/textual/enter_leave_css_selector.py", line 9, in <module>
    class EnterLeave(App):
  File "/home/x/Archive/python/2024/textual/enter_leave_css_selector.py", line 14, in EnterLeave
    @on(Enter, "Button")
  File "/home/x/.local/lib/python3.10/site-packages/textual/_on.py", line 69, in on
    raise OnDecoratorError(
textual._on.OnDecoratorError: The message class must have a 'control' to match with the on decorator

Textual Diagnostics

Versions

Name	Value
Textual	0.83.0
Rich	13.8.1

Python

Name	Value
Version	3.10.12
Implementation	CPython
Compiler	GCC 11.4.0
Executable	/usr/bin/python3

Operating System

Name	Value
System	Linux
Release	6.9.3-76060903-generic
Version	#202405300957171834820922.04~7817b67 SMP PREEMPT_DYNAMIC Mon J

Terminal

Name	Value
Terminal Application	Alacritty
TERM	alacritty
COLORTERM	truecolor
FORCE_COLOR	Not set
NO_COLOR	Not set

Rich Console options

Name	Value
size	width=229, height=43
legacy_windows	False
min_width	1
max_width	229
is_terminal	True
encoding	utf-8
max_height	43
justify	None
overflow	None
no_wrap	False
highlight	None
markup	None
height	None
It will be helpful if you run the following command and paste the results:

Example Code

#!/usr/bin/python

from textual import on
from textual.app import App
from textual.events import Enter, Leave
from textual.widgets import Button


class EnterLeave(App):
    def compose(self):
        yield Button("Hello")

    @on(Enter, "Button")
    @on(Leave, "Button")
    def hover_button(self, event):
        button = self.query_one(Button)

        if event.handler_name == "on_enter":
            button.label = "Hovering" 

        else:
            button.label = "Hello" 

EnterLeave().run()

Without the selectors it works fine, but then I have to check within the method if I'm entering or leaving a specific widget I want to act on:

#!/usr/bin/python

from textual import on
from textual.app import App
from textual.events import Enter, Leave
from textual.widgets import Button


class EnterLeave(App):
    def compose(self):
        yield Button("Hello")

    @on(Enter)
    @on(Leave)
    def hover_button(self, event):
        button = self.query_one(Button)

        if event.handler_name == "on_enter":
            button.label = "Hovering" 

        else:
            button.label = "Hello" 

EnterLeave().run()

[github-actions]

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

• How do I center a widget in a screen?
• How do I fix WorkerDeclarationError?
• Why doesn't Textual look good on macOS?
• No widget called TextLog

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

This is an automated reply, generated by FAQtory