r - Shiny Dashboard - display a dedicated "loading.." page until initial loading of the data is done

Question

I have initial loading of data from the DB in the server.R which takes a few seconds. Until this is done, the page displayed is distorted (wrong data in selection box, and weird placing of the boxes, see below).

I want to display a different page (or at least different content in my first-displayed tab) until the data is completely loaded.

I thought about doing some kind of conditionalPanel using a condition based on a dedicated global variable (initial_loading_done), but wherever I tried placing the conditionalPanel it didn't work.

This is the structure of my UI.R:

shinyUI(

  dashboardPage(
    dashboardHeader(title = "Title"),
    dashboardSidebar(
       sidebarMenu(
           menuItem("Tab1", tabName = "Tab1",icon = icon("dashboard")),
           menuItem("Tab2", tabName = "Tab2",  icon = icon("bar-chart-o"))
       )
    ),
    dashboardBody(
       includeCSS("custom_css.css"),
       tabItems(
           tabItem(tabName = "Tab1", 
                   fluidRow(<content>),
                   mainPanel(
                      fluidRow(<content>)
                   )
           ),
           tabItem(tabName = "Tab2",
                  fluidRow(<content>),
                  mainPanel(
                      dataTableOutput('my_data_table')  
                  )
           )
       )
    )
 )
)

Answer 1

Here's a very simple example using shinyjs package

The idea is to create the loading "page" and the content "page" under different IDs, have the content page initially hidden, and use show() and hide() after the app is ready

library(shiny)
library(shinyjs)

load_data <- function() {
  Sys.sleep(2)
  hide("loading_page")
  show("main_content")
}

ui <- fluidPage(
  useShinyjs(),
  div(
    id = "loading_page",
    h1("Loading...")
  ),
  hidden(
    div(
      id = "main_content",
      "Data loaded, content goes here"
    )
  )
)

server <- function(input, output, session) {
  load_data()
}

shinyApp(ui = ui, server = server)