Multiple action buttons with one event handler in Shiny? - r

Question

I'd like to have a variable number of identical actionButton()s on a page all handled by one observeEvent() function.
For example, in a variable-length table of tables, I'd like each interior table to have a button that links to more information on that table.
In standard HTML, you do this with a simple form, where you use a hidden input to designate the interior table number, like this:
<form ...>
<input id="table_number" type="hidden" value="1"/>
<input type="submit" value="Examine"/>
</form>
When a button is pressed, you can examine the hidden input to see which one it was.
Is there a way to do this in Shiny? The only solution I've come up with is to give each actionButton() it's own inputId. This requires a separate observeEvent() for each button. Those have to be created ahead of time, imposing a maximum number of buttons.

Answer 1

It only took me a couple of years, but I now have a much better answer to this question. You can use a JavaScript/jQuery function to put an on-click event handler on every button in a document, then use the Shiny.onInputChange() function to pass the ID of a button (<button id="xxx"...) that has been clicked to a single observer in your Shiny code.
There's a full description with code examples at One observer for all buttons in Shiny using JavaScript/jQuery

Answer 2

You could use shiny modules for this: you can have variable number of actionButton that are identical. These are defined in the ab_moduleUI part. They are handled by their own observeEvent but it has to be defined only once in the ab_module part.
With lapply any number of actionButton can be created.
Edit: You don't have to specify the number of buttons beforehand: use renderUI to generate UI elements at server side.
For demonstration purposes I added a numericInput to increase/decrease the number of modules to render.
# UI part of the module
ab_moduleUI <- function(id){
ns <- NS(id)
tagList(
fluidRow(
actionButton(ns("btn"), paste("ActionButton", id, sep="-")),
textOutput(ns("txt"))
)
)
}
# Server part of the module
ab_module <- function(input, output, session){
observeEvent(input$btn,{
output$txt <- renderText("More information shown")
})
}
# UI
ui <- fluidPage(
# lapply(paste0("mod", 1:no_btn), ab_moduleUI)
numericInput("num", "Number of buttons to show" ,value = 5, min = 3, max = 10),
uiOutput("ui")
)
# Server side
server <- function(input, output, session){
observeEvent(input$num, {
output$ui <- renderUI({
lapply(paste0("mod", 1:input$num), ab_moduleUI)
})
lapply(paste0("mod", 1:input$num), function(x) callModule(ab_module, x))
})
}
shinyApp(ui, server)
Read more about shiny modules here

Answer 3

Regarding the use of Shiny modules to answer my original question...
What I'd like to have is a way to have multiple buttons on a page that can be handled by a single observeEvent(), which is easy to do with traditional HTML forms, as shown in the original question.
GyD's demonstration code using Shiny modules almost solves the problem, but it doesn't actually return which button was pressed to the main server. It took me a long time, but I finally figured out how to write a module that does let the main server know which button was pressed:
actionInput <- function(id) {
ns <- NS(id)
tagList(
textInput(ns("text"), label=NULL, value=id),
actionButton(ns("button"), "OK")
)
}
action <- function(input, output, session) {
eventReactive(input$button, {
return(input$text)
})
}
ui <- fluidPage(fluidRow(column(4, actionInput("b1")),
column(4, actionInput("b2")),
column(4, uiOutput("result"))))
server <-function(input, output, session) {
b1 <- callModule(action, "b1")
observeEvent(b1(), {
output$result = renderText(b1())
})
b2 <- callModule(action, "b2")
observeEvent(b2(), {
output$result = renderText(b2())
})
}
shinyApp(ui = ui, server = server)
(In a real application, I would make the textInputs invisible, as they're only there to provide an id for which button was pressed.)
This solution still requires an observeEvent() in the main server for each button. It may be possible to use modules in some other way to solve the problem, but I haven't been able to figure it out.
My original alternative, using a separate observeEvent() in the main server for each button, is actually quite a bit simpler than an expansion of this demo code would be for a hundred or more buttons.