On

Decorator to declare that the method is a message handler.

The decorator accepts an optional CSS selector that will be matched against a widget exposed by a control property on the message.

Example

# Handle the press of buttons with ID "#quit".
@on(Button.Pressed, "#quit")
def quit_button(self) -> None:
    self.app.quit()

Keyword arguments can be used to match additional selectors for attributes listed in ALLOW_SELECTOR_MATCH.

Example

# Handle the activation of the tab "#home" within the `TabbedContent` "#tabs".
@on(TabbedContent.TabActivated, "#tabs", pane="#home")
def switch_to_home(self) -> None:
    self.log("Switching back to the home tab.")
    ...

Parameters:

Name	Type	Description	Default
message_type	type[Message]	The message type (i.e. the class).	required
selector	str | None	An optional selector. If supplied, the handler will only be called if selector matches the widget from the control attribute of the message.	None
**kwargs	str	Additional selectors for other attributes of the message.	{}