Support progress indicators

[kamilzyla]

With Shiny it is possible to report progress of a long running computation (using either the functional or object-oriented API). Many React libraries provide components which could be used instead (e.g. Spinner and ProgressIndicator from Fluent UI), however it is difficult to use them as Shiny is super vigilant about delaying any rendering until all computations are finished. It is possible to hack around this problem to some extent, e.g.:

library(shiny)
library(shiny.fluent)

shinyApp(
  ui = Stack(tokens = list(childrenGap = 10), style = list(width = 200),
    PrimaryButton.shinyInput("start", text = "Start Computation"),
    reactOutput("spinner")
  ),
  server = function(input, output) {
    computing <- reactiveVal(FALSE)
    trigger <- debounce(computing, 5) # Enough delay for Shiny to render the Spinner first
    observeEvent(input$start, computing(TRUE))
    observeEvent(trigger(), {
      if (trigger()) {
        Sys.sleep(3) # Long computation
        computing(FALSE)
      }
    })
    output$spinner <- renderReact({
      if (computing()) Spinner(size = 3)
    })
  }
)

Still, this is far from being a drop-in replacement for the progress reporting functionality in base Shiny.

[kamilzyla]

It would be great to be able to use progress indicators in a similar fashion to this (Slack discussion):

plotly::plotlyOutput("plot") |> shinycssloaders::withSpinner()

[OrangeIcecubes]

Thanks for sharing, very helpful