Dynamic UI where UI of one module is injected into another module.

app.R

library(shiny)

filtersUI <- function(id) {
  ns <- NS(id)
  
  fluidRow(
    uiOutput(ns("filters"))
  )
}

filters <- function(input, output, session, tabselected, subfilters) {
  
  output$filters <- renderUI({
    req(tabselected())
    subfilters[[tabselected()]]
  })
}

subfilter1UI <- function(id) {
  ns <- NS(id)
  fluidRow(
    textOutput(ns("filter"))
  )
}

subfilter1UI2 <- function(id) {
  ns <- NS(id)
  tagList(
    uiOutput(ns("select1")),
    uiOutput(ns("select2"))
  )
}

subfilter1 <- function(input, output, session) {
  
  ns <- session$ns
  
  model <- reactive({
    req(!is.null(input$select1))
    unique(mpg$model[mpg$class == input$select1])
  })
  
  output$select1 <- renderUI({
          selectizeInput(ns("select1"), "Class", choices = unique(mpg$class))
  })
  
  output$select2 <- renderUI({
          selectizeInput(ns("select2"), "Model", choices = model())

  })
  
  
  output$filter <- renderText(input$select2)
  
  invisible()
}

subfilter2UI <- function(id) {
  ns <- NS(id)
  fluidRow(
    textOutput(ns("filter"))
  )
}

subfilter2UI2 <- function(id) {
  ns <- NS(id)
  tagList(
    uiOutput(ns("select1")),
    uiOutput(ns("select2"))
  )
}

subfilter2 <- function(input, output, session) {
  
  ns <- session$ns
  
  model <- reactive({
    req(!is.null(input$select1))
    unique(mpg$model[mpg$manufacturer == input$select1])
  })
  
  output$select1 <- renderUI({
    selectizeInput(ns("select1"), "Manufacturer", choices = unique(mpg$manufacturer))
  })
  
  output$select2 <- renderUI({
    selectizeInput(ns("select2"), "Model", choices = model())
    
  })
  
  
  output$filter <- renderText(input$select2)
  
  invisible()
}

ui <- fixedPage(
  wellPanel(
    subfilter1UI("subfilter1")
  ),
  wellPanel(
    subfilter2UI("subfilter2")
  ),
  wellPanel(
    filtersUI("filters")
  ),
  wellPanel(
    selectInput("tabselected", "Select:", c("first" = "first", "second" = "second"))
  )
)

server <- function(input, output, session) {
  tabselected = reactive(input$tabselected)
  callModule(subfilter1, "subfilter1")
  callModule(subfilter2, "subfilter2")
  callModule(filters, "filters", tabselected, subfilters = list("first" = subfilter1UI2("subfilter1"),
                                                                "second" = subfilter2UI2("subfilter2")))
}


shinyApp(ui, server)