How to use renderUI in shiny modules. Main takeaway: session$ns("id"). This works in nested modules, too. See the section on session$ns in the documentation for more information: http://shiny.rstudio.com/reference/shiny/latest/session.html

uiOutput-in-modules.R

library(shiny)
library(dplyr)
library(ggplot2)


innerModUI <- function(id) {
  ns <- NS(id)
  
  fluidPage(fluidRow(
    uiOutput(ns("inner_slider")),
    plotOutput(ns("inner_plot"))
  ))
}

innerMod <- function(input, output, session) {
  output$inner_slider <- renderUI({
    sliderInput(session$ns("slider2"), label = "inner module slider", min = round(min(mtcars$mpg)), 
      max = round(max(mtcars$mpg)), value = c(min(mtcars$mpg), max(mtcars$mpg), step = 1))
  })
  
  output$inner_plot <- renderPlot({
    req(input$slider2)
    data <- filter(mtcars, between(mpg, input$slider2[1], input$slider2[2]))
    ggplot(data, aes(mpg, wt)) + geom_point()
  })
}

outerModUI <- function(id) {
  ns <- NS(id)
  fluidPage(fluidRow(
    uiOutput(ns("outer_slider")),
    plotOutput(ns("outer_plot")),
    innerModUI(ns("inner"))
  ))
}

outerMod <- function(input, output, session) {
  callModule(innerMod, "inner")
  
  output$outer_slider <- renderUI({
    sliderInput(session$ns("slider1"), label = "outer module slider", min = round(min(mtcars$mpg)), 
      max = round(max(mtcars$mpg)), value = c(min(mtcars$mpg), max(mtcars$mpg), step = 1))
  })
  
  output$outer_plot <- renderPlot({
    req(input$slider1)
    data <- filter(mtcars, between(mpg, input$slider1[1], input$slider1[2]))
    ggplot(data, aes(mpg, wt)) + geom_point()
  })
}

ui <- fluidPage(
  fluidRow(
    outerModUI("outer")
  )
)

server <- function(input, output, session) {
  callModule(outerMod, "outer")
  
}

shinyApp(ui = ui, server = server)

Nice example except it does not work. I am using R3.6.2 and Shiny 1.6.0. I cannot get the second slider Input to work.

@boeingguy2, I posted this a few years ago so it's quite likely that it doesn't work anymore. If you figure out how to get this to work, please feel free to post here so others may benefit.

Thanks so much for this example, it helped me figure out how to resolve a complex nested module problem I was having.

I believe the error message generated in the example is due to incorrect bracket placement in the sliderinput lines of code.

This line (appears twice in the example):
value = c(min(mtcars$mpg), max(mtcars$mpg), step = 1))

Should be this:
value = c(min(mtcars$mpg), max(mtcars$mpg)), step = 1)

session$ns("id") is a life saver, thank you.