Express: Cannot create a navbar page with an id and a sidebar

[gadenbuie]

It's common to want to add a global sidebar to a navbar page and to have some content in that sidebar be displayed conditionally. With Shiny Core, you can create an app with this layout using the following code:

from shiny import App, ui

ui = ui.page_navbar(
    ui.nav_panel("A", "Page A content"),
    ui.nav_panel("B", "Page B content"),  # <2>
    title="App with navbar",
    fillable=True,
    id="page",  # <1>
    sidebar=ui.sidebar(
        ui.input_select("data", "Data", ("A", "B", "C")),
        ui.panel_conditional(
            "input.page === 'B'",  # <3>
            ui.input_select("subset", "Subset for B", ("e", "f", "g")),
        ),
    ),
)


def server(input):
    pass


app = App(ui, server)

shinylive.io example

There are three components:

1. The ui.page_navbar() needs the id argument.
2. When id is provided, the current page title is reported at that input.{id}.
3. ui.panel_conditional() can use the value of the input, e.g. input.page === 'B', to display content only when nav_panel("B", ...) is displayed.

In Shiny Express, this pattern is not possible because users cannot set id via ui.page_opts(). In theory, they would need to provide a custom function to ui.page_opts(page_fn=) that passes id to shiny.ui.page_navbar().

from shiny.express import input, ui
from functools import partial
from shiny.ui import page_navbar

def page_navbar_id(*args, **kwargs):
    return page_navbar(*args, **kwargs, id="page")

## Doesn't work
ui.page_opts(title="App with navbar", fillable=True, page_fn=page_navbar_id)
## Does work, but can't set the page `id`
# ui.page_opts(title="App with navbar", fillable=True)

with ui.sidebar(title="Settings"):
    ui.input_select("data", "Data", ("A", "B", "C"))

    with ui.panel_conditional("input.page === 'Settings B'"):
        ui.input_select("subset", "Subset for B", ("e", "f", "g"))

with ui.nav_panel("A"):
    "Page A content"

with ui.nav_panel("B"):
    "Page B content"

shinylive.io example

This doesn't work, however, because the special handling for the top-level with ui.sidebar() only happens when page_fn is None.

py-shiny/shiny/ui/_page.py

Lines 543 to 545 in 340858a

	if page_fn is None:
	if nNavs == 0:
	if nSidebars == 0:

py-shiny/shiny/ui/_page.py

Line 556 in 340858a

elif nSidebars == 1:

Attempting to run the example above using ui.page_opts(page_fn) gives the following error

Traceback (most recent call last):
  File "/Users/garrick/work/posit-dev/py-shiny/shiny/express/_run.py", line 60, in wrap_express_app
    app_ui = run_express(file).tagify()
             ^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/Users/garrick/work/posit-dev/py-shiny/venv/lib/python3.12/site-packages/htmltools/_core.py", line 735, in tagify
    cp.children = cp.children.tagify()
                  ^^^^^^^^^^^^^^^^^^^^
  File "/Users/garrick/work/posit-dev/py-shiny/venv/lib/python3.12/site-packages/htmltools/_core.py", line 222, in tagify
    tagified_child = child.tagify()
                     ^^^^^^^^^^^^^^
  File "/Users/garrick/work/posit-dev/py-shiny/venv/lib/python3.12/site-packages/htmltools/_core.py", line 735, in tagify
    cp.children = cp.children.tagify()
                  ^^^^^^^^^^^^^^^^^^^^
  File "/Users/garrick/work/posit-dev/py-shiny/venv/lib/python3.12/site-packages/htmltools/_core.py", line 222, in tagify
    tagified_child = child.tagify()
                     ^^^^^^^^^^^^^^
  File "/Users/garrick/work/posit-dev/py-shiny/shiny/ui/_navs.py", line 396, in tagify
    nav, content = render_navset(
                   ^^^^^^^^^^^^^^
  File "/Users/garrick/work/posit-dev/py-shiny/shiny/ui/_navs.py", line 1314, in render_navset
    selected = x.get_value()
               ^^^^^^^^^^^
AttributeError: 'Sidebar' object has no attribute 'get_value'

[gadenbuie]

We're going to move forward with passing kwargs (#1314), but we also discussed that this situation would be improved by resolving #939.