How to correctly use a checkboxInput 'All/None' in a uiOutput context in R Shiny?

Here is the context :

library(shiny)

liste_statut <- c("A","B","C")

ui <- shinyUI(fluidPage(uiOutput("testUI")))
server <- function(input, output, session) {

   output$testUI <- renderUI({

    navbarPage(
      title = "Test",

  tabPanel(icon = icon("users"), 'Test',

           sidebarPanel(
             # Statut
             checkboxGroupInput("statut", "Statut", liste_statut, liste_statut),
             checkboxInput('selectall_statut', 'Tout / Aucun', T))))

})

  # observe({
  #   updateCheckboxGroupInput(
  #     session, 'statut', choices = liste_statut,
  #     selected = if (input$selectall_statut) liste_statut
  #   )
  # })
}

 shinyApp(ui = ui, server = server)

I would like to use my checkbox All/None (in comment lines) properly cause in this case i have a "Warning: Error in if: argument is of length zero". Where should i put it or maybe should i redefine properly something in the UI part?

I willingly use the renderUI/uiOutput option (contrary to the "standard mode" ui/server) because in future, i will add an authentification module, so be able to display several "panels" according to user.

Thanks and sorry for my terrible english :).

Solution

The following works for me:

library(shiny)
liste_statut <- c("A","B","C")

ui <- shinyUI(fluidPage(uiOutput("testUI")))
server <- function(input, output, session) {

  output$testUI <- renderUI({

    navbarPage(
      title = "Test",

      tabPanel(icon = icon("users"), 'Test',

               sidebarPanel(
                 # Statut
                 checkboxGroupInput("statut", "Statut", liste_statut, liste_statut),
                 checkboxInput('selectall_statut', 'Tout / Aucun', T))))

  })

  observeEvent(input$selectall_statut,{
    val <- liste_statut
    if(!input$selectall_statut)
      val <- character(0)

    updateCheckboxGroupInput(
      session, 'statut', 
      selected = val
    )
  })
}

I initially tried selected = ifelse(input$selectall_statut, liste_statut, character(0)) instead of the intermediate variable val. However, ifelse() only returned a single value, not a vector.

If you are going to do this many times over, then I would recommend a custom ifelse function. Perhaps something like the following:

ifelse2 <- function(test, yes, no){
    if(test)
        return(yes)
    return(no)
}