闪亮：在 downloadHandler 中使用 validate()

Question

我有一个闪亮的应用程序，一旦单击按钮就会打印报告。通过 downloadHandler() 函数创建报告。

我希望在导出报告之前有一个强制输入字段；合适的 Shiny 函数是 validate() (https://shiny.rstudio.com/articles/validation.html)。

但是，根据文档，validate() 函数只能用于 reactive() 或 render() 函数：

To use this validation test in your app, place it at the start of any reactive or render* expression that calls input$data. 

我没有找到可以将此函数放入我的 downloadHandler 函数的地方。有人知道这怎么可能吗？

这里是相关的代码部分；我希望创建报告时必须填写“公司名称”字段。

ui <- fluidPage(

  sidebarLayout(
    position = "left",

    sidebarPanel(

      textInput(
        inputId = "company_name",
        label = "Company name", 
        value = ""
      ),
    )
  )
)

server <- function(input, output) {
  output$report <- downloadHandler(
    filename = "report.pdf",
    content = function(file) {
      # Copy the report file to a temporary directory before processing it, in
      # case we don't have write permissions to the current working dir (which
      # can happen when deployed).
      tempReport <- file.path(tempdir(), "report.Rmd")
      file.copy("report.Rmd", tempReport, overwrite = TRUE)
      dir.create(file.path(tempdir(),"www"))
      file.copy("www", file.path(tempdir()), recursive=TRUE)      

      # Set up parameters to pass to Rmd document
      params <- list(company_name = input$company_name)

      # Knit the document, passing in the `params` list, and eval it in a
      # child of the global environment (this isolates the code in the document
      # from the code in this app).

      rmarkdown::render(tempReport, output_file = file,
                        params = params,
                        envir = new.env(parent = globalenv())
      )
    }
  )
}

Answer 1

问题在于downloadButton 是一个输入小部件，而validate 应该与输出一起使用。

如果您的下载要求未得到满足，我的解决方法是隐藏（或禁用）downloadButton。这可以通过shinyjs 来完成，它允许您通过 id 隐藏或禁用按钮。

library(shiny)

ui <- fluidPage(
  shinyjs::useShinyjs(),
  textInput("text", "content", "", placeholder = "please insert something"),
  shinyjs::hidden(downloadButton("download"))
)

server <- function(input, output, session) {
  output$download <- downloadHandler(
    filename = "file.csv",
    content = function(file) {
      write.csv(data.frame(content = input$text), file)
    }
  )

  observeEvent(input$text, {
    if (input$text == "")
      shinyjs::hide("download")
    else
      shinyjs::show("download")
  })
}

shinyApp(ui, server)

将hide/show/hidden 替换为enable/disable/disabled 以始终显示按钮，但在input$text 为空时使其不可点击。