在 R Shiny 服务器上保存临时文件

Question

I have been trying to solve a problem in developing one of my first R Shiny apps. My app works on my laptop, but I can't get it to work when I upload it on the Shiny server. I want the app to create a temporary file of the scatterplot, plotOut, on the server, which is then exported to the Excel file, either upon clicking the 'Download Scatterplot' button or automatically. I am posting my best attempt at a reprex below. I believe I need to use tempdir() in some way, but not sure how. Thanks in advance :D

"ui.R"

library(tidyverse)

library(openxlsx)

 

ui <- fluidPage(

  fluidRow("This is a simplified app to reproduce the difficulties in saving and downloading files on the Shiny server",
           plotOutput("plot", height = 350),
           downloadButton('downloadPlot1', "Download ScatterPlot"),
           downloadButton(
             'dl_excel',
             'Download Results (.xlsx)'
           )
  )
)

"server.R"

server <- function(input, output){
  ###create basic plot in ggplot
  plotOut <- reactive(
    ggplot(mtcars, aes(x=wt, y=mpg)) + geom_point()
  )
 
  ###display plot
  output$plot <- renderPlot({
    plotOut()
  })

  #temp = tempdir() #tried using this in filename to no avail

  fName = paste0('plotOut', Sys.Date(), '.png')

  ##save plot file as png
  output$downloadPlot1 <- downloadHandler(
    filename = function(){fName},
    content = function(file){
      ggsave(file,plot=plotOut())
    })

  ##format excel file for output
  output$dl_excel <- downloadHandler(
    filename = function(){
      paste0('results_', Sys.Date(), '.xlsx')
    },
    content = function(file){
      my_workbook <- createWorkbook()
      addWorksheet(
        wb = my_workbook,
        sheetName = "Sheet1"
      )

      insertImage(my_workbook, sheet = 1,
        file = fName
        , width = 4, height = 4, startRow = 1, startCol = 1, units = "in", dpi = 300
      )
      saveWorkbook(my_workbook, file)
    }
  )
}

Answer 1

Someone in a different forum helped me solve this. Updating the code to the following resolves the issue.

output$dl_excel <-
      downloadHandler(
        filename = function() {
          paste0('results_', Sys.Date(), '.xlsx')
        },

        content = function(file) {
          **tempPNG <- tempfile(fileext = ".png") #create a tempfile to print the plot to
          ggsave(tempPNG, plot = plotOut()) #print the plot to the tempfile**

          my_workbook <-
            createWorkbook()
          addWorksheet(wb = my_workbook,
                       sheetName = "Sheet1")
          insertImage(
            my_workbook,
            sheet = 1,
            **file = tempPNG, #use the tempfile**

            width = 4,
            height = 4,
            startRow = 1,
            startCol = 1,
            units = "in",
            dpi = 300
          )            
          saveWorkbook(my_workbook, file)
        }
      )