Usage of UIOutput in multiple menuItems in R shiny

The R shiny script below displays "output$brand_selector" output in subItem1. I wish to display the same output in subItem2 and subItem3. Please help, also when I open the dashboard, the output is present by default, I wish to make it appear only when I click on a subItem, thanks and please help.

candyData <- read.table(
text = "
Brand       Candy           value
Nestle      100Grand        Choc1
Netle       Butterfinger    Choc2
Nestle      Crunch          Choc2
Hershey's   KitKat          Choc4
Hershey's   Reeses          Choc3
Hershey's   Mounds          Choc2
Mars        Snickers        Choc5
Nestle      100Grand        Choc3
Nestle      Crunch          Choc4
Hershey's   KitKat          Choc5
Hershey's   Reeses          Choc2
Hershey's   Mounds          Choc1
Mars        Twix            Choc3
Mars        Vaid            Choc2",
header = TRUE,
stringsAsFactors = FALSE)
library(shiny)
library(shinydashboard)
ui <- dashboardPage(
dashboardHeader(),
dashboardSidebar(
sidebarMenu(

  id = "tabs",
  menuItem("Charts", icon = icon("bar-chart-o"),
           menuSubItem("Sub-item 1", tabName = "subitem1"),
           menuSubItem("Sub-item 2", tabName = "subitem2"),
           menuSubItem("Sub-item 3", tabName = "subitem3")
  ))),
dashboardBody(
tabItems(tabItem("subitem1", uiOutput("brand_selector")),
         tabItem("subitem2", 4),
         tabItem("subitem3", 7))
))
server <- function(input, output,session) {
observeEvent(input$Select1,{
updateSelectInput(session,'Select2',

choices=unique(candyData$Candy[candyData$Brand==input$Select1]))
}) 
observeEvent(input$Select2,{
updateSelectInput(session,'Select3',

choices=unique(candyData$value[candyData$Brand==input$Select1 & 
candyData$Candy==input$Select2]))
})
output$brand_selector <- renderUI({
box(title = "Data", status = "primary", solidHeader = T, width = 12,
    fluidPage(
      fluidRow(

        column(2,offset = 0, style='padding:1px;',  
 selectInput("Select1","select1",unique(candyData$Brand))),
        column(2,offset = 0, 
  style='padding:1px;',selectInput("Select2","select2",choices = NULL)),
        column(2, offset = 0, 
  style='padding:1px;',selectInput("Select3","select3",choices=NULL ))
      )))
  })}
  shinyApp(ui = ui, server = server)

You could create a dummy tabItem which is hidden and select that bu default. This will give the illusion that no tabItem is selected. To hide the tabItem option you could use hidden function from shinyjs package.

Following is the modified ui code:

ui <- dashboardPage(
    dashboardHeader(),
    dashboardSidebar(
      sidebarMenu(
       shinyjs::useShinyjs(),
        id = "tabs",
        menuItem("Charts", icon = icon("bar-chart-o"),
                 shinyjs::hidden(menuSubItem("dummy", tabName = "dummy")),
                 menuSubItem("Sub-item 1", tabName = "subitem1"),
                 menuSubItem("Sub-item 2", tabName = "subitem2"),
                 menuSubItem("Sub-item 3", tabName = "subitem3")
        ))),
    dashboardBody(
      tabItems(tabItem("dummy"),
              tabItem("subitem1", uiOutput("brand_selector")),
               tabItem("subitem2", 4),
               tabItem("subitem3", 7))
    ))

EDIT1: As per the comments and reference from the answers given bu Joe here you can do that as follows:

candyData <- read.table(
    text = "
    Brand       Candy           value
    Nestle      100Grand        Choc1
    Netle       Butterfinger    Choc2
    Nestle      Crunch          Choc2
    Hershey's   KitKat          Choc4
    Hershey's   Reeses          Choc3
    Hershey's   Mounds          Choc2
    Mars        Snickers        Choc5
    Nestle      100Grand        Choc3
    Nestle      Crunch          Choc4
    Hershey's   KitKat          Choc5
    Hershey's   Reeses          Choc2
    Hershey's   Mounds          Choc1
    Mars        Twix            Choc3
    Mars        Vaid            Choc2",
    header = TRUE,
    stringsAsFactors = FALSE)
  library(shiny)
  library(shinydashboard)
  ui <- dashboardPage(
    dashboardHeader(),
    dashboardSidebar(
      sidebarMenu(
       shinyjs::useShinyjs(),
        id = "tabs",
        menuItem("Charts", icon = icon("bar-chart-o"),
                 shinyjs::hidden(menuSubItem("dummy", tabName = "dummy")),
                 menuSubItem("Sub-item 1", tabName = "subitem1"),
                 menuSubItem("Sub-item 2", tabName = "subitem2"),
                 menuSubItem("Sub-item 3", tabName = "subitem3")
        ))),
    dashboardBody(
      tabItems(tabItem("dummy"),
              tabItem("subitem1", uiOutput("brand_selector")),
               tabItem("subitem2", uiOutput("brand_selector1")),
               tabItem("subitem3", uiOutput("brand_selector2")))
    ))
  server <- function(input, output,session) {


    observeEvent(input$Select1,{
      updateSelectInput(session,'Select2',

                        choices=unique(candyData$Candy[candyData$Brand==input$Select1]))
    }) 
    observeEvent(input$Select2,{
      updateSelectInput(session,'Select3',

                        choices=unique(candyData$value[candyData$Brand==input$Select1 & 
                                                         candyData$Candy==input$Select2]))
    })
    output$brand_selector1 <-  output$brand_selector2 <-  output$brand_selector <- renderUI({
      box(title = "Data", status = "primary", solidHeader = T, width = 12,
          fluidPage(
            fluidRow(

              column(2,offset = 0, style='padding:1px;',  
                     selectInput("Select1","select1",unique(candyData$Brand))),
              column(2,offset = 0, 
                     style='padding:1px;',selectInput("Select2","select2",choices = NULL)),
              column(2, offset = 0, 
                     style='padding:1px;',selectInput("Select3","select3",choices=NULL ))
            )))
    })}
  shinyApp(ui = ui, server = server)

EDIT2:

Here is a slightly different approach without using renderUI and using shinyModule:

candyData <- read.table(
  text = "
  Brand       Candy           value
  Nestle      100Grand        Choc1
  Netle       Butterfinger    Choc2
  Nestle      Crunch          Choc2
  Hershey's   KitKat          Choc4
  Hershey's   Reeses          Choc3
  Hershey's   Mounds          Choc2
  Mars        Snickers        Choc5
  Nestle      100Grand        Choc3
  Nestle      Crunch          Choc4
  Hershey's   KitKat          Choc5
  Hershey's   Reeses          Choc2
  Hershey's   Mounds          Choc1
  Mars        Twix            Choc3
  Mars        Vaid            Choc2",
  header = TRUE,
  stringsAsFactors = FALSE)
library(shiny)
library(shinydashboard)

submenuUI <- function(id) {
  ns <- NS(id)
  tagList(
    box(title = "Data", status = "primary", solidHeader = T, width = 12,
              fluidPage(
                fluidRow(

                  column(2,offset = 0, style='padding:1px;',
                         selectInput(ns("Select1"),"select1",unique(candyData$Brand))),
                  column(2,offset = 0,
                         style='padding:1px;',selectInput(ns("Select2"),"select2",choices = NULL)),
                  column(2, offset = 0,
                         style='padding:1px;',selectInput(ns("Select3"),"select3",choices=NULL ))
                )))
        )

}

# submenu <- function(input,output,session){}
submenuServ <- function(input, output, session){

  observeEvent(input$Select1,{
    updateSelectInput(session,'Select2',

                      choices=unique(candyData$Candy[candyData$Brand==input$Select1]))
  })
  observeEvent(input$Select2,{
    updateSelectInput(session,'Select3',

                      choices=unique(candyData$value[candyData$Brand==input$Select1 &
                                                       candyData$Candy==input$Select2]))
  })

}




ui <- dashboardPage(
  dashboardHeader(),
  dashboardSidebar(
    sidebarMenu(
      shinyjs::useShinyjs(),
      id = "tabs",
      menuItem("Charts", icon = icon("bar-chart-o"),
               shinyjs::hidden(menuSubItem("dummy", tabName = "dummy")),
               menuSubItem("Sub-item 1", tabName = "subitem1"),
               menuSubItem("Sub-item 2", tabName = "subitem2"),
               menuSubItem("Sub-item 3", tabName = "subitem3")
      ))),
  dashboardBody(
    tabItems(tabItem("dummy"),
             tabItem("subitem1", submenuUI('submenu1')),
             tabItem("subitem2", submenuUI('submenu2')),
             tabItem("subitem3", submenuUI('submenu3'))
             )
  ))
server <- function(input, output,session) {

  callModule(submenuServ,"submenu1")
  callModule(submenuServ,"submenu2")
  callModule(submenuServ,"submenu3")

}
shinyApp(ui = ui, server = server)

Hope it helps!