r - Display selected folder path in Shiny

Question

I want my Shiny app to allow user specify a path to a folder (locally) and display the selected path. The following code works but I can't figure out how to hide "character(0)" in verbatimTextOutput until the folder was selected. I tried conditional panel (see commented out in my code) but can't figure out what to use as a condition here (because shinyDirButton is not a standard action button...). Thank you!

library(shiny)
library(shinyFiles)

# Define UI for application that draws a histogram
ui <- fluidPage(

  # Application title
  mainPanel(
    shinyDirButton("dir", "Input directory", "Upload"),
    #conditionalPanel(
      #condition = "???",
      verbatimTextOutput('dir')
    #)
  )
)

server <- function(input, output) {

  shinyDirChoose(input, 'dir', roots = c(home = '~'), filetypes = c('', 'txt','bigWig',"tsv","csv","bw"))

  dir <- reactive(input$dir)
  output$dir <- renderPrint({parseDirPath(c(home = '~'), dir())})

  observeEvent(
    ignoreNULL = TRUE,
    eventExpr = {
      input$dir
    },
    handlerExpr = {
      home <- normalizePath("~")
      datapath <<- file.path(home, paste(unlist(dir()$path[-1]), collapse = .Platform$file.sep))
    }
  )
}


# Run the application 
shinyApp(ui = ui, server = server)

The closest question I was able to find is this but it doesn't solve my problem: R conditionalPanel reacts to output

Answer 1

In the server function, use renderText instead of renderPrint:

library(shiny)
library(shinyFiles)

# Define UI for application that draws a histogram
ui <- fluidPage( # Application title
  mainPanel(
    shinyDirButton("dir", "Input directory", "Upload"),
    verbatimTextOutput("dir", placeholder = TRUE)  # added a placeholder
  ))

server <- function(input, output) {
  shinyDirChoose(
    input,
    'dir',
    roots = c(home = '~'),
    filetypes = c('', 'txt', 'bigWig', "tsv", "csv", "bw")
  )

  dir <- reactive(input$dir)
  output$dir <- renderText({  # use renderText instead of renderPrint
    parseDirPath(c(home = '~'), dir())
  })

  observeEvent(ignoreNULL = TRUE,
               eventExpr = {
                 input$dir
               },
               handlerExpr = {
                 home <- normalizePath("~")
                 datapath <<-
                   file.path(home, paste(unlist(dir()$path[-1]), collapse = .Platform$file.sep))
               })
}

# Run the application
shinyApp(ui = ui, server = server)