R - count Shiny download button clicks

Question

Is there a built in Shiny attribute that counts the number of times a downloadButton is clicked? I\'m not finding it in the function help or web searches. If there\'s not

Answer 1

I think there is no build-in method. But you could build it yourself.

You can do this by adding a click listener to the button with javascript:

  observe({
    if(is.null(input$rnd)){
      runjs("
            var click = 0;
            Shiny.onInputChange('rnd', click)
            var dwnldBtn = document.getElementById('dwnldBtn')
            dwnldBtn.onclick = function() {click += 1; Shiny.onInputChange('rnd', click)};
            ")      
    }
  })

The output from Shiny.onInputChange('rnd', click) will be accessible in Shiny via input$rnd.

Edit: For multiple buttons you can use:

  observe({
    for(btn1 in 1:2){
      if(is.null(input[[paste0("rnd", btn1)]])){
        runjs(
          paste0("
              var counter", btn1 ,"= 0;
              var dwnldBtn = document.getElementById('", paste0("dwnldBtn", btn1), "')
              dwnldBtn.onclick = function() {counter", btn1, " +=1; Shiny.onInputChange('", paste0("rnd", btn1), "', counter", btn1,")};
              ")
        )      
      }
    }
  })

For a working example see below:

   library(shiny)
library(shinyjs)
data <- matrix(1:20, nrow=5)

ui <-  fluidPage(title = 'Count Button Clicks',
                 useShinyjs(),
                 fluidRow(style = "padding-bottom: 20px;",
                          column(width=6,
                                 textOutput("actionclickCount"),
                                 br(),
                                 textOutput("downloadclickCount")
                          ),
                          column(width=6,
                                 actionButton("actionBtn", "Action Button"),
                                 br(),
                                 downloadButton("dwnldBtn", "Download Button")
                          )
                 )
)

server <- function(input, output, session) {
  output$actionclickCount <- renderText({
    paste('Action Button Clicks =',input$actionBtn)
  })

  output$downloadclickCount <- renderText({
    paste('Download Button Clicks =', input$rnd)
  })

  output$dwnldBtn <- downloadHandler(
    filename = 'data.csv',
    content = function(file){
      write.csv(data, file)
    },
    contentType = 'csv'
  )

  observe({
    if(is.null(input$rnd)){
      runjs("
            var click = 0;
            Shiny.onInputChange('rnd', click)
            var dwnldBtn = document.getElementById('dwnldBtn')
            dwnldBtn.onclick = function() {click += 1; Shiny.onInputChange('rnd', click)};
            ")      
    }
    })

  }

runApp(shinyApp(ui = ui, server = server), launch.browser = TRUE)