Shiny + DT: how to make datatable reactive?

I have a problem when trying to make a datatable reactive in a shiny app (from the DT package). Here's my reproducible example:

ui.r

dashboardPage(

  dashboardHeader(title = "TEST reactive DT"),

  dashboardSidebar(
    sidebarMenu(
      menuItem("See data", tabName = "db"),
      menuItem("Test", tabName = "test")),
      radioButtons("rb1", label = "Select data", 
                 choices = list("IRIS" = "iris", "CARS" = "cars"),
                 selected = "iris")
    ),

  dashboardBody(
    tabItems(
      tabItem(tabName = "db",
              h4("Show selected dataset"),
              fluidRow(DT::dataTableOutput('tbl')) #THIS DOES NOT WORK (NOT REACTIVE)
              ),
      tabItem(tabName = "test",
              h4("Test tab"),
              fluidRow(column(3, verbatimTextOutput("value"))) #THIS WORKS
              )
      )
    )
)  

      

        
        
        
      

    

server.r

library(shiny)
library(shinydashboard)

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

  output$value <- renderPrint({ input$rb1 })

  data <- reactive({
    switch(input$rb1,
           "iris" = iris,
           cars)
  })

  action <- dataTableAjax(session, cars)  # HOW SHOULD I SPECIFY? data() INSTEAD OF cars DOES NOT WORK
  widget <- datatable(cars,  # HOW SHOULD I SPECIFY? data() INSTEAD OF cars DOES NOT WORK
                     class = 'display cell-border compact',
                     filter = 'top',
                     server = TRUE,
                     options = list(ajax = list(url = action))
  )

  output$tbl <- DT::renderDataTable(widget)
}

      

        
        
        
      

    

As you can see in the Test tab, the radio selection is updated when changed. However, I cannot figure out how this should be integrated in the dataTableAjax and dataTable functions, can you explain / help me to solve this problem?

Many thanks for your help!

Regards