title: Using uiOutput in menuSubItem of shinydashboard
body: <p>When I use <code>uiOutput</code> in a <code>menuSubItem</code>, the dropdown menu that I'm trying to dynamically render does not show up. Is this not supported or am I doing something wrong? Here's a reproducible example:</p>
  
  <pre><code>### ui.R
  
  library(shiny)
  library(shinydashboard)
  
  # Create dashboard header
  header &lt;- dashboardHeader()
  
  # Create dashboard sidebar
  sidebar &lt;- dashboardSidebar(
      sidebarMenu(
          menuItem(text="test1", tabName="test1",
                   menuSubItem(icon=NULL, selectInput("x", "X", c("a", "b", "c"), selected="a")),
                   menuSubItem(icon=NULL, uiOutput("y"))
          )
      )
  )
  
  # Create dashboard body
  body &lt;- dashboardBody()
  
  shinyUI(
      dashboardPage(
          skin="purple",
          header,
          sidebar,
          body
      )
  )
  </code></pre>
  
  <p>'</p>
  
  <pre><code>### server.R
  
  library(shiny)
  
  shinyServer(function(input, output, session) {
      output$y &lt;- renderUI({
          y_ &lt;- switch(input$x,
                   a=1:10,
                   b=11:20,
                   c=21:30)
  
          selectInput("y", "Y", y_)
      })
  
  })
  </code></pre>