Dashboard with multiple tabs (shiny.router), all tabs load on start

[shahreyar-abeer]

In a shiny.fluent dashboard with multiple tabs (navigation handled with shiny.router), all the tabs load on start.
Thus slowing down the app.
Is there any solution to this?

[jakubsob]

Hi @shahreyar-abeer,

It's hard to tell what exactly causes your app to slow down without an example, but I've created a simple app that I think illustrates the issue. Let me know if this is what you're struggling with.

library(shiny)
library(shiny.fluent)
library(shiny.router)

router <- make_router(
  route(
    "/",
    tagList(
      Label("Home page")
    )
  ),
  route(
    "hidden",
    tagList(
      Label("Hidden page"),
      textOutput("text")
    ),
    server = function(input, output, session) {
      output$text <- renderText({
        Sys.sleep(5)
        "Delayed text"
      })
    }
  )
)

ui <- fluentPage(router$ui)
server <- function(input, output, session) {
  router$server(input, output, session)
}

shinyApp(ui, server)

this app takes 5 seconds to open due to a Sys.sleep call. In order not to run server code on hidden pages we can introduce a reactive which tracks if given page has been opened:

library(shiny)
library(shiny.fluent)
library(shiny.router)

router <- make_router(
  route(
    "/",
    tagList(
      Label("Home page")
    )
  ),
  route(
    "hidden",
    tagList(
      Label("Hidden page"),
      textOutput("text")
    ),
    server = function(input, output, session) {
      opened <- reactiveVal(FALSE)
      observe({
        # Set `opened` reactive to indicate whether this page has been opened
        # It runs only once, after page has been opened for the first time
        if (!opened()) {
          opened(shiny.router::get_page() == "hidden")
        }
      })

      output$text <- renderText({
        shiny::req(opened())
        Sys.sleep(5)
        "Delayed text"
      })
    }
  )
)

ui <- fluentPage(router$ui)
server <- function(input, output, session) {
  router$server(input, output, session)
}

shinyApp(ui, server)

The app opens instantly. When we go to /hidden page we wait 5 seconds for the text to appear. Then we can go to / and back to /hidden and the text is still there (we don't wait 5 seconds) as it hasn't been invalidated by opened (which is invalidated once in the observer).

Does this help you speed up your app?

[shahreyar-abeer]

Thanks a lot!
This is exactly what I required.

[rodrigoestrellac]

In case you have some reactive output that should not be calculated if the page is hidden what would be the best approach ??
For example, I have a reactive expression that is used to render a bar plot on one page and a scatter plot on another. If the active page is the one with the bar plot, and the reactive expression changes, only the bar plot should be recalculated.

I guess the quicker way would be to create a reactive expression like this:
activePage <- reactive({ shiny.router::get_page() })

And then every output expression should start with req(activePage() == "pageName"), where pageName is the name of the page where the output is placed.

In the example I gave it should look like this
`output$barplot <- renderPlot({
req(activePage() == "barplotPage")

plot
})

output$scatter_plot <- renderPlot({
req(activePage() == "scatter_plotPage")

plot
})
`

Am I right ? Is there a more efficient way to achieve this behaviour ??

Thanks !