Disable button in UI based on input from module in Shiny app - r

Question

In a Shiny app, I’m trying to disable/enable an action button in the UI of the main app based on user's input from a module. Basically, I want the “Next Page” (submit) button to be disabled until the user responds to the last item (item3). When the user responds to the last item, I want the button to be enabled. However, my app isn’t updating the toggle state of the action button.
Here’s a minimal reproducible example using a {Golem} structure:
app_ui.R:
library("shiny")
library("shinyjs")
app_ui <- function(request) {
tagList(
useShinyjs(),
fluidPage(
mod_mod1_ui("mod1_ui_1"),
actionButton(inputId = "submit",
label = "Next Page")
)
)
}
app_server.R:
library("shiny")
library("shinyjs")
app_server <- function( input, output, session ) {
state <- mod_mod1_server("mod1_ui_1")
# Enable the "Next Page" button when the user responds to the last item
observe({
toggleState("submit", state == TRUE)
})
}
mod_mod1.R:
library("shiny")
library("shinyjs")
mod_mod1_ui <- function(id){
ns <- NS(id)
tagList(
radioButtons(inputId = ns("item1"),
label = "Item 1",
choices = c(1, 2, 3, 4),
selected = character(0)),
radioButtons(inputId = ns("item2"),
label = "Item 2",
choices = c(1, 2, 3, 4),
selected = character(0)),
radioButtons(inputId = ns("item3"),
label = "Item 3",
choices = c(1, 2, 3, 4),
selected = character(0))
)
}
mod_mod1_server <- function(id){
moduleServer( id, function(input, output, session){
ns <- session$ns
# When the user completes the last survey question
completed <- logical(1)
observe({
lastQuestion <- input$item3
if(!is.null(lastQuestion)){
completed <- TRUE
} else {
completed <- FALSE
}
browser()
})
return(completed)
})
}
Using browser() statements, it appears that the completed variable is correctly being updated in the module, but that the state variable isn’t updating in the main app.

Answer 1

I am not clear if you want this to work when the user responds to only item3 or all items (1 thru 3). I am assuming that it is the latter. However, you can modify as your use case requires it. Defining a reactiveValues object works. Try this
library("shiny")
library("js")
mod_mod1_ui <- function(id){
ns <- NS(id)
tagList(
radioButtons(inputId = ns("item1"),
label = "Item 1",
choices = c(1, 2, 3, 4),
selected = character(0)),
radioButtons(inputId = ns("item2"),
label = "Item 2",
choices = c(1, 2, 3, 4),
selected = character(0)),
radioButtons(inputId = ns("item3"),
label = "Item 3",
choices = c(1, 2, 3, 4),
selected = character(0))
)
}
mod_mod1_server <- function(id){
moduleServer( id, function(input, output, session){
ns <- session$ns
# When the last survey question is completed
rv <- reactiveValues(completed=1)
observe({
lastQuestion <- input$item3
if(!is.null(lastQuestion) & !is.null(input$item2) & !is.null(input$item1)){
rv$completed <- 1
} else {
rv$completed <- 0
}
print(rv$completed )
#browser()
})
return(rv)
})
}
app_ui <- function(request) {
fluidPage(
useShinyjs(),
tagList(
mod_mod1_ui("mod1_ui_1"),
actionButton(inputId = "submit",
label = "Next Page")
)
)
}
app_server <- function( input, output, session ) {
state <- mod_mod1_server("mod1_ui_1")
# Don't show "Next Page" button until last item is completed
observe({
toggleState("submit", state$completed == TRUE)
})
}
shinyApp(ui = app_ui, server = app_server)