Get the current image name of a slickR slideshow in shiny

Question

Below is a shiny app which displays a slideshow of images with the slickR package. How to get the name of the current image?

library(shiny)
library(slickR)

ui <- fluidPage(
  tags$div(
      slickROutput("slickr", width="500px"),
      style = "margin-left:100px;"
  )
)

server <- function(input, output) {

  imgs <- list.files("~/", pattern=".png", full.names = TRUE)

  output[["slickr"]] <- renderSlickR({
    slickR(imgs)
  })

}

# Run the application 
shinyApp(ui = ui, server = server)

Answer 1

Here is a solution with a MutationObserver:

library(shiny)
library(slickR)

js <- "
$(document).ready(function(){
  var ss = document.getElementById('slickr');
  // create an observer instance
  var observer = new MutationObserver(function(mutations) {
    var index = $(ss).find('.slick-current').data('slick-index');
    Shiny.setInputValue('imageIndex', parseInt(index)+1);
  });
  // configuration of the observer
  var config = {subtree: true, attributes: true};
  // observe 
  observer.observe(ss, config);
})
"

ui <- fluidPage(
  tags$head(
    tags$script(HTML(js))
  ),
  textOutput("imgName"),
  tags$hr(),
  tags$div(
      slickROutput("slickr", width="500px"),
      style = "margin-left:100px;"
  )
)

server <- function(input, output) {

  imgs <- list.files("~/", pattern=".png", full.names = TRUE)

  output[["slickr"]] <- renderSlickR({
    slickR(imgs)
  })

  output[["imgName"]] <- renderText({
    paste0("CURRENT IMAGE: ", basename(imgs[input[["imageIndex"]]]))
  })

}

# Run the application 
shinyApp(ui = ui, server = server)

Another solution, simpler: replace js with

js <- "
$(document).ready(function(){
  $('#slickr').on('setPosition', function(event, slick) {
    var index = slick.currentSlide + 1;
    Shiny.setInputValue('imageIndex', index);
  });
})"