How to create dynamic number of observeEvent in another observeEvent? - r

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)

Answer 1

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.