r - 仅当输出出现在主面板中时，Shiny R中的显示下载按钮

Question

我有下面的代码，它允许接受csv文件->运行R代码->显示->下载输出。

但是，下载按钮会在应用程序运行后立即出现。
是否只有在输出文件可用时才显示输出按钮的方法？

以下是我正在使用的代码:

UI.R

library(shiny)

#ui.R
# Define UI for random distribution application 
shinyUI(fluidPage(

  # Application title
  titlePanel("Text Mining on R"),

  sidebarLayout(
    sidebarPanel(
      fileInput('file1', 'Select the Input File',
                accept=c('text/csv','text/comma-separated-values,text/plain','.csv')),
      tags$hr(),
      fileInput('file2', 'Select the UserTopic file',
                accept=c('text/csv','text/comma-separated-values,text/plain','.csv'))

    ),
    mainPanel(
      dataTableOutput('table'),
      downloadButton('OutputFile', 'Download Output File')
    )
  ))
)

服务器。R

#server.R
library(shiny)

shinyServer(function(input, output) {

  observe({
    file1 = input$file1
    file2 = input$file2
    if (is.null(file1) || is.null(file2)) {
      return(NULL)
    }
    data1 = read.csv(file1$datapath,header = TRUE, sep=",",skipNul = TRUE)
    data2 = read.csv(file2$datapath,header = TRUE, sep=",",skipNul = TRUE)
   source("RCode.R", local = TRUE)
    #output$table <- renderDataTable(output2)
    output$table <- renderDataTable({
      my_function(file1$datapath,file2$datapath)
    })

    output$OutputFile <- downloadHandler(


      filename = function() {
        paste("OutputFile", "_",Sys.time(),".csv",sep="")
       },

      content = function(file) {


        write.csv(my_function(file1$datapath,file2$datapath), file, sep = ",",
                    row.names = FALSE)
      }
    )
  })

})

谢谢!

Answer 1

在服务器端，您可以使用:

output$download <- renderUI({
  if(!is.null(input$file1) & !is.null(input$file2)) {
    downloadButton('OutputFile', 'Download Output File')
  }
})

在ui端，您将下载按钮替换为:

uiOutput("download")