How to create dynamic number of observeEvent in another observeEvent?

Question

Here I asked an similar question and got a working answer. But the solution does not work if 'actionButton' of sub segment is replace by 'selectInput'. On each selection of selectInput creates two outputs. Please help.. Thanks....

library(shiny)

ui <- fluidPage(
  verbatimTextOutput("txt",placeholder = T), #"It is Created for Testing"
  actionButton("addSeg", "Add a Segment"),
  uiOutput("myUI")
)

server <- function(input, output, session) {
  alld <- reactiveValues()
  alld$ui <- list()

  # Action to add new Segment
  observeEvent(input$addSeg,{
    new_id <- length(alld$ui) + 1
    sub_name <- paste0("addSub_", new_id)

    alld$ui[[new_id]] <- list(selectInput(sub_name,"Add a variable", choices = c("V1","V2"), selected  = NULL))

    observeEvent(input[[sub_name]], {
      new_text_id <- length(alld$ui[[new_id]]) + 1
      alld$ui[[new_id]][[new_text_id]] <- HTML(paste0("Variable ",input[[sub_name]]," added<br>"))
    }, ignoreInit = TRUE)
  })

  output$myUI <- renderUI({alld$ui})

  output$txt <- renderText({class(alld$ui)})
}

shinyApp(ui, server)

@amrrs This is a sample code. The replacement is needed in my original shiny app which is more complex.. — Raja Saha, Jan 22 '19 at 12:59

score 3 · Accepted Answer · answered Jan 22 '19 at 12:59

This behaviour occurs because the custom UI element is re-rendered every time a new element is added to the list. Once you click "V2" and the new text element is added, the selectInput itself re-renders and resets to V1, which is noticed by the observer you've created.

The following might be a solution for you:

  observeEvent(input$addSeg,{
    new_id <- length(alld$ui) + 1
    sub_name <- paste0("addSub_", new_id)

    alld$ui[[new_id]] <- list(
      selectInput(sub_name,
                  "Add a variable",
                  choices = c("", "V1","V2"),
                  selected  = "")
      )

    observeEvent(input[[sub_name]], {
      if (input[[sub_name]] == "") return()
      new_text_id <- length(alld$ui[[new_id]]) + 1
      alld$ui[[new_id]][[new_text_id]] <- HTML(paste0("Variable ",input[[sub_name]]," added<br>"))
    }, ignoreInit = TRUE)
  })

What I've done here is add an empty option to your selectInputs, and a condition to the corresponding observer that it shouldn't do anything if the input is empty. This way, I'm harnessing the "resetting" behaviour to be useful instead of annoying.

If this solves your problem, please mark it solved @RajaSaha — amrrs, Jan 22 '19 at 13:11

How to create dynamic number of observeEvent in another observeEvent?

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