sub_pages_router.on_path_changed

[davetapley]

I was about to post asking for a path change callback for a sub pages parent, and that I had a workaround using ui.on and window.navigation.addEventListener("navigate", but when searching the code for the type of the ui.on callback and I see:

nicegui/nicegui/elements/sub_pages.js

Line 60 in b1b818d

emitEvent("sub_pages_navigate", stripPathPrefix(href));

and:

nicegui/nicegui/sub_pages_router.py

Lines 21 to 22 in b1b818d

	on('sub_pages_open', lambda event: self._handle_open(event.args))
	on('sub_pages_navigate', lambda event: self._handle_navigate(event.args))

Questions:

1. I don't see it mentioned in the docs, but I assume it's a stable and public API?

2. Is there any reason it's on ui.context.client.sub_pages_router and not accessible from the ui.sub_pages element?

   I see it's assigned, but doesn't have a public getter:
   

   nicegui/nicegui/elements/sub_pages.py

   Line 45 in b1b818d

   self._router = context.client.sub_pages_router

---

For context I needed the callback to simplify using a ui.footer per @falkoschindler 's suggestion here:

• Complex, page specific ui.footer with sub pages #5436 (comment)

By doing this I don't have to worry about calling footer.clear() in sub pages to ensure the previous page's content is cleared out:

    def on_path_change(_path: str) -> None:
        footer.clear()

    ui.context.client.sub_pages_router.on_path_changed(on_path_change)

[falkoschindler]

Hi @davetapley,

1. I don't see it mentioned in the docs, but I assume it's a stable and public API?

It's probably stable, but technically I wouldn't consider it public API. A dedicated change event for ui.sub_pages would certainly be a useful feature.

2. Is there any reason it's on ui.context.client.sub_pages_router and not accessible from the ui.sub_pages element?

I think this is because there's usually no need for the user to access the router.