How to display a busy indicator when querying data

shiny
1

I'm using the python version of shiny (for the first time) and I'm having trouble finding documentation/examples on the user of spinners / busy indicators. I'm using base rather than express. The documentation for ui.busy_indicators.use implies that the default is "enabled" but I cannot get it to work.

My ui code is

app_ui = ui.page_fixed(
    ui.layout_sidebar(
        ui.sidebar(
            ui.input_date_range("daterange", "Date range", start="2024-01-01"),
            ui.input_action_button("refresh", "Refresh"),
        ),
        ui.layout_columns(
            ui.card(
                ui.card_header("Plot"),
                output_widget("chart"),
            )
        ),
    ),
    ui.busy_indicators.use(spinners=True, pulse=True, fade=True),
)

And my server has a single function that renders an altair chart. It works but it takes a while to fetch and display the data and there's no feedback.

def server(input, output, session):
    @render_altair
    @reactive.event(input.refresh)
    def chart():
        df = data.read_data(start_date=input.daterange()[0], end_date=input.daterange()[1])
       ...
      return alt.Chart(df)...

I'd like some form of spinner to display while the server chart method is executing. How do I do this?

2

I found Executing on a different thread/process which seems to work. I'm not sure if there's an easier way but it solves my problem.