Export plots to PDF from reactive/observeEvent

I have below renderPlot inside observeEvent as i am dynamically plotting (histogram + boxplot) based on dynamic user selection of tests. Everything is working fine. What I need now is to be able to save whatever plots rendered & save into PDF. I tried to basically copy the whole codes inside the renderPlot into downloadHandler (with pdf(file) & dev.off() blanketing the codes) but it is not working & I am getting below error:

Warning: Error in if: argument is of length zero
[No stack trace available]

pdf file was created but 0 byte (so nothing saved).

    output[[plotname]]<- renderPlot({
      req(input$param) #aes string input for single plot

      mybin <- input$bin
      col = as.name(input$param[my_i]) #take the next parameters from the list
      datcol <- as.data.frame(myval()[input$param])
      lims  <- as.data.frame(lims()[input$param])
      ll    <- lims[1,my_i]
      hl    <- lims[2,my_i]
      ave   <- round(mean(datcol[[my_i]]), digits = 4)

      histop <- hist(my_i, mybin, col, datcol, lims, ll, hl, ave)

      boxp   <- bp(my_i, mybin, col, datcol, lims, ll, hl)
      chart_align(histop, boxp)

I'd recommend starting by creating a reprex so that other people can actually help you. You can read some advice on that in https://mastering-shiny.org/action-workflow.html#getting-help.

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As I said above, if you want to get help, you need to make it easier for people by providing a reprex. There is no way to tell what's going wrong with your code because there's no way to run it.

Hi @hadley,

Thank you for the reply.
Basically, the blocker i am facing now is getting the plots into the PDF document.
Below is my downloadHandler codes which is not working.
But if I just replace the print line with like plot(x=my_n, y=my_n), the PDF export works.

    output$pdfDL <- downloadHandler(
      filename = "pplots.pdf",
      content <- function(file) {
        pdf(file, width = 10, height = 7)
        mp= length(myPlot)
         for (n in 1:mp) {   
            my_n <- n