can not see my second tabitem after clicking action button

[sgr308]

Hi
I am learning Shiny to develop an App.

I have two tabItems in sidebar where first one is simple home page and in another, user has to upload the .txt file.

After click on submit button I want to see the uploaded file contents but I can not see the second tabitem contents in my dashboardBody after clicking on action button.

Can someone please let me know if I am missing something in this code??

The code is here:

# Upload library ----
library(shiny)
library(shinydashboard)

ui <- dashboardPage(
  dashboardHeader(title = "First App"),
  dashboardSidebar(
    sidebarMenu(
      id = "tabs",
      menuItem("About", tabName = "first", icon = icon("home")),
      menuItem("Upload Data", tabName = "second", icon = icon("home"),
               fileInput("file1", "Upload a .txt file",
                         accept = c("text/csv", "text/comma-separated-values,text/plain",".csv",
                                    options(shiny.maxRequestSize=900*1024^2))),
      actionButton('submit', 'Submit!!'))
    )
  ),
  dashboardBody(
    tabItems(
    tabItem(tabName = "first",
            h3("App Ver 0.1.0")
            ),
    tabItem(tabName = "second",
            h2("Results Table"),
            tableOutput("contents")
            )
          )
  )
)
server <- function(input, output, session) {
  observeEvent(input$submit, {
    updateTabItems(session, "tabs", selected = "first" )
  })
  output$contents <- renderTable(rownames = TRUE,{
    if (is.null(input$file1)) return(NULL)
    head(read.csv(input$file1$datapath))
  })
}
shinyApp(ui, server)

[ismirsehregal]

For future readers: here you can find a workaround.