Conditional controls and screen output

Conditional controls

Sometimes you don’t want your user to be able to go to the next screen if a condition based on inputs is not met. This can be done in shinyglide with the next_condition argument of the screen function. This option takes exactly the same syntax has the one used in shiny::conditionalPanel.

For example, in the following app, the Next button is disabled until the n value is greater then zero :

ui <- fluidPage(
  glide(
    screen(
      next_condition = "input.n > 0",
      
      p("Please choose a value for n :"),
      numericInput("n", "n :", value = 0)
    ),
    screen(
      p("Here is your plot :"),
      plotOutput("plot")
    )
  )
)

server <- function(input, output, session) {
  output$plot <- renderPlot({
    hist(rnorm(input$n), main = paste("n =", input$n))
  })
}

shinyApp(ui, server)

You can do the same for the Back button with the previous_condition argument.

By default the button is disabled when the condition is not met (more precisely, the button gets a disabled = "disabled" argument and a disabled CSS class). If you prefer to hide it entirely, you can add disable_type = "hide" to your glide() definition :

ui <- fluidPage(
  glide(
    disable_type = "hide",
    
    screen(
      next_condition = "input.n > 0",
      
      p("Please choose a value for n :"),
      numericInput("n", "n :", value = 0)
    ),
    screen(
      p("Here is your plot :"),
      plotOutput("plot")
    )
  )
)

server <- function(input, output, session) {
  output$plot <- renderPlot({
    hist(rnorm(input$n), main = paste("n =", input$n))
  })
}

shinyApp(ui, server)

Screen output

Sometimes you want to show a screen only if certain conditions are met based on inputs. For example, if a user chooses a value which is not present in a dataset, you would like to display a specific screen to alert him.

This is possible by using a screenOutput call in you app UI, associated to a renderUI in your app server. If renderUI returns NULL, the screen will be hidden.

Here is an example :

ui <- fluidPage(
  glide(
    disable_type = "hide",
    
    screen(
      p("Do you want to see the next screen ?"),
      checkboxInput("check", "Yes, of course !", value = FALSE)
    ),
    screenOutput("check_screen"),
    screen(
      p("And this is the last screen")
    )
  )
)

server <- function(input, output, session) {
  output$check_screen <- renderUI({
    if(!input$check) return(NULL)
    p("Here it is !")
  })
  outputOptions(output, "check_screen", suspendWhenHidden = FALSE)
}

shinyApp(ui, server)

Important : for the screenOutput to work, it is mandatory to add the following line in your app server :

outputOptions(output, "your_screen_id", suspendWhenHidden = FALSE)

Otherwise, it won’t be updated when hidden.

Sometimes the screenOutput computation takes some time. In these cases, with the default controls, the Next button is disabled and a Loading message is shown until the next screens computations is done. You can see it in the following example, which is the same as the previous one but with an articial 2 seconds waiting time :

ui <- fluidPage(
  glide(
    disable_type = "hide",
    
    screen(
      p("Do you want to see the next screen ?"),
      checkboxInput("check", "Yes, of course !", value = FALSE)
    ),
    screenOutput("check_screen"),
    screen(
      p("And this is the last screen")
    )
  )
)

server <- function(input, output, session) {
  output$check_screen <- renderUI({
    Sys.sleep(2)
    if(!input$check) return(NULL)
    p("Here it is !")
  })
  outputOptions(output, "check_screen", suspendWhenHidden = FALSE)
}

shinyApp(ui, server)