R Shiny: downloadHandler — проблема в аргументе содержимого

У меня есть приложение Shiny, и я хочу загрузить график в формате png с помощью кнопки загрузки и команды «downloadHandler». Как вы можете видеть в приведенном ниже коде, он должен использовать input$question для имени файла. Когда я нажимаю кнопку загрузки, все, что я получаю, это «downplot» в качестве имени файла и никакой реакции, когда я пытаюсь сохранить файл. Загрузка таблицы работает нормально... Любая помощь/совет?

library(shiny)
library(shinydashboard)
library(dplyr)
library(likert)
library(DT)
library(ggplot2)
library(likert)



levels.netusoft <- c("Sehr wenig", "Etwas", "Stark", "Sehr stark", "Verweigert", 
                     "Weiß nicht", "Keine Antwort")
levels.ppltrst <- c("1", "2", "3", "4", "5", "6", "Verweigert", "Weiß nicht", 
                    "Keine Antwort")
levels.polintr <- c("Überhaupt nicht", "Sehr wenig", "Etwas", "Stark", "Sehr stark", 
                    "Verweigert", "Weiß nicht", "Keine Antwort")
levels.psppsgva <- c("Überhaupt nicht fähig", "Wenig fähig", "Ziemlich fähig", 
                     "Sehr fähig", "Vollkommen fähig", "Verweigert", "Weiß nicht", 
                     "Keine Antwort")
levels.actrolga <- c("Wenig fähig", "Ziemlich fähig", "Sehr fähig", "Vollkommen fähig", 
                     "Verweigert", "Weiß nicht", "Keine Antwort")
levels.gndr <- c("männlich", "weiblich")

dataset <- data.frame("netusoft" = factor(sample(levels.netusoft, 100, 
                                                 replace = TRUE),
                                          levels.netusoft),
                      "ppltrst" = factor(sample(levels.ppltrst, 100, 
                                                replace = TRUE),
                                         levels.ppltrst),
                      "polintr" = factor(sample(levels.polintr, 100, 
                                                replace = TRUE),
                                         levels.polintr),
                      "psppsgva" = factor(sample(levels.psppsgva, 100, 
                                                 replace = TRUE),
                                          levels.psppsgva),
                      "actrolga" = factor(sample(levels.actrolga, 100, 
                                                 replace = TRUE),
                                          levels.actrolga),
                      "gndr" = factor(sample(levels.gndr, 100,
                                             replace = TRUE),
                                      levels.gndr),
                      check.names = FALSE)



# ----- UI
ui <- fluidPage(
  dashboardPage(
    dashboardHeader(title = "European Social Survey Österreich Dashboard", 
                    titleWidth = 300),
    dashboardSidebar(width = 300,
                     selectInput(inputId = "round", 
                                 label = "Wählen Sie eine ESS Runde aus",  
                                 c("ESS 9" = "9"),
                                 selected = "9", selectize = FALSE), 
                     #end selectinput
                     conditionalPanel(
                       condition = "input.round == '9'",
                       selectInput(inputId = "battery", 
                                   label = "Wählen Sie Themenfeld aus",
                                   c("A: Medien-, Internetnutzung, Soziales Vertrauen" = "A",
                                     "B: Politische Variablen, Immigration" = "B"), 
                                   selectize = FALSE), #end selectinput
                       uiOutput("question_placeholder")
                     ),
                     checkboxInput(
                       inputId = "group",
                       label = "Daten gruppieren",
                       value = FALSE), #end checkbox
                     
                     conditionalPanel(
                       condition = "input.group == true",
                       selectInput(
                         inputId = "UV",
                         label = "Daten gruppieren nach:",
                         c("Geschlecht" = "gndr")
                       ) # end conditionalPanel
                     )
    ), # end dashboardSidebar
    dashboardBody(
      fluidRow(
        box(width = 7, status = "info", solidHeader = TRUE,
            title = "Table:",
            dataTableOutput("tabelle", width = "100%")
        ),
        
        downloadButton("downtable", "Tabelle speichern"),
        #  tags$br(),
        tags$hr(),
        
        box(width = 8, status = "info", solidHeader = TRUE,
            title = "Graph:",
            plotOutput("plot", width = "auto", height = 500)
        )
      ), # end fluidRow
      
      downloadButton("downplot", "Grafik speichern"),
      #  tags$br(),
      tags$hr() # end fluidRow
      
    ) #end dashboardBody
  )
)

server <- function(input, output, session) {
  get_data <- reactive({
    req(input$question)
    if (input$group) {
      dataset %>% 
        select(Antwortkategorie = input$question, req(input$UV)) %>% 
        group_by(grp = !!as.symbol(input$UV), Antwortkategorie)
    } else {
      dataset %>% 
        select(Antwortkategorie = input$question) %>% 
        group_by(Antwortkategorie)
    } 
  })
 

  
  output$question_placeholder <- renderUI({
    if (input$battery == "A") {
      choices <- c("A2|Häufigkeit Internetnutzung" = "netusoft",
                   "A4|Vertrauen in Mitmenschen" = "ppltrst")
    } else if (input$battery == "B") {
      choices <- c("B1|Interesse an Politik" = "polintr",
                   "B2|Politische Mitsprachemöglichkeit" = "psppsgva",
                   "B3|Fähigkeit politischen Engagements " = "actrolga")
    }
    selectInput(inputId = "question", 
                label = "Wählen Sie eine Frage aus",
                choices,
                selectize = FALSE)
  })
  
  output$tabelle <- renderDataTable({
    tab <- datatable(get_data() %>% 
                summarize(n = n()) %>% 
                mutate(Prozent = n / sum(n),
                       "Kum. Prozent" = cumsum(Prozent)),
              rownames = FALSE) %>% 
      formatPercentage(c("Prozent","Kum. Prozent"), 1) 
  
    if (input$group==TRUE) {
      tab <- get_data() %>%
        summarize(n = n()) %>% 
        #  mutate(Prozent = n / sum(n)) %>% 
        #  mutate(Prozent = percent((n / sum(n)), accuracy = 0.01)) %>% 
        pivot_wider(
          #id_cols = grp, #wird angezeigt
          names_from = grp,
          values_from = n) 
    }
    tab
    })
  
  output$downtable <- downloadHandler(
    filename = function() {
      paste(input$question, ".csv", sep = "")
    },
    content = function(file) {
      
      tab <- get_data() %>%  
        summarize(n = n()) %>% 
        mutate(Prozent = percent((n / sum(n)), accuracy = 0.01)
        )
      
      if (input$group==TRUE) {
        tab <- get_data() %>%
          summarize(n = n()) %>% 
          #  mutate(Prozent = n / sum(n)) %>% 
          #   mutate(Prozent = percent(n, accuracy = 0.01)) %>% 
          pivot_wider(
            #id_cols = grp, #wird angezeigt
            names_from = grp,
            values_from = n) 
      }
      
      write.csv(tab, file, row.names = FALSE)
    }
  )
  
  output$plot <- renderPlot({
    dat <- get_data()
    lik <- likert(dat %>% ungroup() %>% select(Antwortkategorie) %>% 
                    as.data.frame(),
                  grouping = if (input$group) dat %>% pull(grp))
    plot(lik)
  })

  output$downplot <- downloadHandler(
    filename = function() {
      paste(input$question, ".png", sep = "")
    }, 
    content = function(file) {
      png(file)
      
      dat <- get_data()
      lik <- likert(dat %>% ungroup() %>% select(Antwortkategorie) %>% 
                      as.data.frame(),
                    grouping = if (input$group) dat %>% pull(grp))
    #  print(lik)
      
      dev.off()
    },
    contentType = "image/png"
  )

}

shinyApp(ui, server)