Shiny: Feature requested: Get the event which is fired in ObserveEvent

[philibe]

Hello,

From my question below in stackoverflow I was surprised that the functionality of getting the event which is fired in ObserveEvent() apparently doesn't exist by default in observeEvent().

• SO: Get the event which is fired in Shiny and with grep (generated input)

I've looked for "event fired" in the issues and the Shiny docs but I didn't found it :)

Have a good day.

Here is the copy-paste of the stackoverflow workaround by ismirsehregal

ui <- fluidPage(
  tags$head(
    tags$script(
      "$(document).on('shiny:inputchanged', function(event) {
          if (event.name != 'changed') {
            Shiny.setInputValue('changed', event.name);
          }
        });"
    )
  ),
  numericInput("a_1", "a_1", 0),
  textInput("a_2", "a_2"),
  textInput("c", "c"),
  textInput("d", "d"),

  p("changedInputs:"), textOutput("changedInputs"), br(),
  p("aFired:"), textOutput("aFired")
)

server <- function(input, output, session) {
  output$changedInputs <- renderText({
    paste("Outside observer: Latest input fired:", paste(input$changed, collapse = ", "))
  })

  myText <- reactiveVal()

  observeEvent(eventExpr = {
    lapply(grep(pattern = "^a_+[[:digit:]]$|^c$", x = isolate({names(input)}), value = TRUE), function(x){input[[x]]})
  }, handlerExpr = {
    req(input$changed)
    if (input$changed == "a_1") {
      myText("Inside observer: input$a_1 was fired")
    } else  if (input$changed == "a_2") {
      myText("Inside observer: input$a_2 was fired")
    } else {
      myText(paste("Inside observer:", input$changed, "was fired"))
    }
  }, ignoreInit = TRUE)

  output$aFired <- renderText({myText()})

}

shinyApp(ui, server)

[ismirsehregal]

Here is a simplified example showing the mentioned workaround (based on the JS event shiny:inputchanged) to receive the input names which triggered observeEvent(). The SO example might be a little difficult to get into.

library(shiny)

ui <- fluidPage(
  tags$head(
    tags$script(
      "$(document).on('shiny:inputchanged', function(event) {
          if (event.name != 'changed') {
            Shiny.setInputValue('changed', event.name);
          }
        });"
    )
  ),
  sliderInput("a", "input$a", 0, 10, 5),
  sliderInput("b", "input$b", 0, 10, 5),
  sliderInput("c", "input$c", 0, 10, 5),
  textOutput("printChangedInputs"),
  textOutput("printTrigger")
)

server <- function(input, output, session) {
  observeEventTrigger <-  reactiveVal()

  observeEvent(c(input$a, input$b), {
    observeEventTrigger(req(input$changed))
    cat("My execution was triggered by input:", observeEventTrigger(), "\n")
  }, ignoreInit = TRUE)

  output$printChangedInputs <- renderText({
    paste("Latest input used:", input$changed)
  })

  output$printTrigger <- renderText({
    paste("Latest observeEvent trigger:", observeEventTrigger())
  })
}

shinyApp(ui, server)

[daattali]

Closely related to https://github.com/rstudio/shiny/issues/1846