R Shiny-文件下载遇到麻烦

Question

So I want to have a Shiny page which: A) Allows the user to upload a .xls file; B) Offers that file back to the user for download as a .csv file; C) Prints the head of the file in the Shiny app to ensure that it was properly read.

Here is the code I am using:

# Want to read xls files with readxl package
library(readxl)
library(shiny)

## Only run examples in interactive R sessions
if (interactive()) {

  ui <- fluidPage(
    fileInput("file1", "Choose File", accept = ".xls"),
    tags$hr(),
    uiOutput("downloader"),
    htmlOutput("confirmText", container = tags$h3),
    tableOutput("listContents")
    )

  server <- function(input, output) {

    theOutput <- reactiveValues(temp = NULL, df = NULL, msg = NULL, fn = NULL)

    observeEvent(input$file1, {
      theOutput$fn <- paste('data-', Sys.Date(), '.csv', sep='')
      theOutput$temp <- read_xls(input$file1$datapath)
      theOutput$msg <- paste("File Contents:")
      theOutput$df <- write.csv(theOutput$temp, 
                                file = theOutput$fn, 
                                row.names = FALSE)
    })

    output$confirmText <- renderText({
      theOutput$msg
    })

    output$listContents <- renderTable({
      head(theOutput$temp)
    })

    output$downloader <- renderUI({
      if(!is.null(input$file1)) {
        downloadButton("theDownload", label = "Download")
        }
      })

    output$theDownload <- downloadHandler(
      filename = theOutput$fn,
      content = theOutput$df
      )
  }

  shinyApp(ui, server)
}

The Shiny page renders correctly, it accepts the upload with no problems, it prints out the head of the .csv with no problems, and it creates a properly formatted "data-{today's date}.csv" file in the same directory as the app.R file.

Problem is, when I hit the download button I get the error message:

Warning: Error in download$func: attempt to apply non-function                                                    
  [No stack trace available]

Can someone tell me what I am doing wrong?

Answer 1

Thanks to the comments above, this is the solution I found (with my comments added, to show where the code changed):

library(readxl) 
library(shiny) 
if (interactive()) {
    ui <- fluidPage(
    fileInput("file1", "Choose File", accept = ".xls"),
    tags$hr(),
    uiOutput("downloader"),
    htmlOutput("confirmText", container = tags$h3),
    tableOutput("listContents")
    )
     server <- function(input, output) {

    theOutput <- reactiveValues(temp = NULL, msg = NULL)

    observeEvent(input$file1, {
      # Do not try to automate filename and the write.csv output here!
      theOutput$temp <- read_xls(input$file1$datapath)
      theOutput$msg <- paste("File Contents:")
    })

    output$confirmText <- renderText({
      theOutput$msg
    })

    output$listContents <- renderTable({
      head(theOutput$temp)
    })

    output$downloader <- renderUI({
      if(!is.null(input$file1)) {
        downloadButton("theDownload", label = "Download")
        }
      })

    output$theDownload <- downloadHandler(
      # Filename and content need to be defined as functions 
      # (even if, as with filename here, there are no inputs to those functions)
      filename = function() {paste('data-', Sys.Date(), '.csv', sep='')},
      content = function(theFile) {write.csv(theOutput$temp, theFile, row.names = FALSE)}
      )   }
     shinyApp(ui, server) }

The fact that content takes an argument (named here "theFile"), which is not called anywhere else, is what was throwing me off.