downloadHandler在使用R Shiny下载图像时出错

如何解决downloadHandler在使用R Shiny下载图像时出错

我花了最后几天尝试添加一个按钮，以在我闪亮的应用程序中下载图像，但我收不到。我之前已经在其他应用程序中完成过此操作，但是这一操作不起作用。该应用程序选择两个图像（或三个图像），并将它们与所需的透明度合并。应用程序中的图像看起来很完美，问题仅在于下载。服务器代码如下；

library(shiny)
library(abind)
library(jpeg)
library(rsconnect)

shinyServer(function(input,output) {

  
output$myImage <- renderImage({
  # A temp file to save the output.

  # Return a list containing the filename and alt text

  
  
  outfile <- tempfile(fileext = '.png')
  
  image1 = jpeg::readJPEG(file.path(
                                    paste(input$map1,'.jpeg',sep='')))
  
  image2 = jpeg::readJPEG(file.path(
                                              paste(input$map2,sep='')))
  
  image3 = jpeg::readJPEG(file.path(
    paste(input$map3,sep='')))


  
  image1 = abind::abind(image1,image1[,1]) # add an alpha channel
  image1[,4] = input$trans1 # set alpha to semi-transparent
  
  image2 = abind::abind(image2,image2[,1]) # add an alpha channel
  image2[,4] = input$trans2

  image3 = abind::abind(image3,image3[,1]) # add an alpha channel
  image3[,4] = input$trans3
  
  if(input$n==0){
    png(outfile,width = 4,height = 4,units = 'in',res = 300)
    par(mai=c(0,0))
    plot.new()
    rasterImage(image1,1,1)
    rasterImage(image2,1)
    dev.off()
  }
  
  if(input$n==1){
    png(outfile,width = 2,height = 2,1)
    
    rasterImage(image3,1)
    dev.off()
  }
  
  
  
  # Return a list containing the filename
  list(src = outfile,contentType = 'image/png',width = 600,height = 400,alt = "This is alternate text")
  
  
},deleteFile = FALSE)


output$downloadImage <- downloadHandler(
  filename = "Image.png",contentType = "image/png",content = function(file) {
    ## copy the file from the updated image location to the final download location
    file.copy(outfile,file)
  }
)  


}

ui代码如下：

library(abind)
library(shiny)
library(rsconnect)
library(jpeg)
library(shiny)
library(shinyBS)
library(shinyjs)

shinyUI(fluidPage(

  
  tags$head(tags$style(
    HTML('
         #sidebar {
     float: right;

         background-color: white;
         border-bottom: 1px solid #e6e6e6;
         border-radius: 0;
         
         }
         
         body,label,input,button,select { 
     font-family: "Open Sans",Arial,sans-serif;
         }')
  )),sidebarLayout(position = "right",sidebarPanel(
   
    
      
      selectInput(inputId = "map1",label = "Mapa 1:",choices = c("Mapa 1","Mapa 2","Mapa 3","Mapa 4","Mapa 5"),selected = "Normal"),sliderInput(inputId = "trans1",label = "Transparencia mapa 1:",min = 0,max = 1,value = 0.5,step = 0.1),selectInput(inputId = "map2",label = "Mapa 2:",sliderInput(inputId = "trans2",label = "Transparencia mapa 2:",hr(),checkboxInput( "n","Anadir otro mapa:",FALSE),conditionalPanel(condition = "input.n==1",selectInput(inputId = "map3",label = "Mapa 3:",selected = "Normal")),sliderInput(inputId = "trans3",label = "Transparencia mapa 3:",step = 0.1)
   ),downloadButton('downloadImage','Download modified image'),hr()
    ),mainPanel(
      imageOutput("myImage")
  )
)))

当我推送下载时，第一件事不是尝试下载“ Image.png”，而是下载了没有扩展名的“ downloadImage”文件。然后，如果我接受，则会出现以下错误：

Anyobdy知道哪个错误？我很绝望！

谢谢

解决方法

outfile在renderImage内部定义，然后在downloadHandler中不存在。因此，请在您的server函数的根目录中定义它：

shinyServer(function(input,output) {

  outfile <- tempfile(fileext = '.png')
  
  output$myImage <- renderImage({
    ......