Shiny modules: Destroy module ui if server-function fails - r

Question

How to display a blank UI (alternatively destroy module UI), if the module server-function fails, without moving all the UI-code to the server function?
Simple reproducible example:
library(shiny)
my_module_ui <- function(id) {
ns <- NS(id)
tags$div(
tags$h1("Don't show me if my_module_server fails!"),
plotOutput(ns("my_plot"))
)
}
my_module_server <- function(input, output, session) {
tryCatch({
my_data <- cars * "A" # fail for demo
# my_data <- cars
output$my_plot <- renderPlot({
cars2 <- my_data + rnorm(nrow(my_data))
plot(cars2)
})
}, error=function(cond) {
message("Destroy UI here!")
})
}
ui <- fluidPage(
my_module_ui("my_id")
)
server <- function(input, output, session) {
callModule(my_module_server, "my_id")
}
shinyApp(ui, server)
My current solution is to have nothing but a uiOutput() in my_module_ui and render the entire ui in the server function. I want to prevent this, since large modules get very messy if all UI-components are placed within the module server-function.
In addition I would preferably also like to avoid returning values from callModule() that destroy the UI and do this from within the server-function instead.
Thanks!

Answer 1

How about you assign a value to the session object and evaluate this value before you create the UI (from server side via renderUI().
1) Move rendering of UI to server side
Use renderUI(my_module_ui("my_id")) on server side and uiOutput("module") on ui side.
2) To detect whether your server module was successful assign a value to the session object
my_module_server <- function(input, output, session) {
tryCatch({
...
session$userData$mod_server <- TRUE
}, error = function(cond) {
session$userData$mod_server <- NULL
})
}
3) Use this value to make the call of your module ui conditional
output$module <- renderUI({
callModule(my_module_server, "my_id")
if(!is.null(session$userData$mod_server)) my_module_ui("my_id")
})
Reproducible example:
library(shiny)
my_module_ui <- function(id) {
ns <- NS(id)
tags$div(
tags$h1("Don't show me if my_module_server fails!"),
plotOutput(ns("my_plot"))
)
}
my_module_server <- function(input, output, session) {
tryCatch({
my_data <- cars * "A" # fail for demo
# my_data <- cars
output$my_plot <- renderPlot({
cars2 <- my_data + rnorm(nrow(my_data))
plot(cars2)
})
session$userData$mod_server <- TRUE
}, error = function(cond) {
session$userData$mod_server <- NULL
})
}
ui <- fluidPage(
uiOutput("module")
)
server <- function(input, output, session) {
output$module <- renderUI({
callModule(my_module_server, "my_id")
if(!is.null(session$userData$mod_server)) my_module_ui("my_id")
})
}
shinyApp(ui, server)

Answer 2

With a little code reordering, and the use of the amazing shinyjs package this can be done.
Note that I added an input to simulate errors and not errors, to see how the UI dissapears. Also all is done in the server part of the module. I hope this will help you. The code has inline comments explaining the steps.
library(shiny)
library(shinyjs)
my_module_ui <- function(id) {
ns <- NS(id)
tagList(
# input added to be able to throw errors and see the ui dissapear
selectInput(
ns('trigger'), 'Error trigger',
choices = list('no error' = c(2,1), 'error' = c('A', 'B')),
selected = 2
),
tags$div(
# div with id, to select it with shinyjs and hide it if necessary
id = ns('hideable_div'),
tags$h1("Don't show me if my_module_server fails!"),
plotOutput(ns("my_plot"))
)
)
}
my_module_server <- function(input, output, session) {
# get all the things prone to error in a reactive call, that way you capture the final
# result or a NULL reactive when an error occurs
foo <- reactive({
tryCatch({
if (input$trigger %in% c(2,1)) {
trigger <- as.numeric(input$trigger)
} else {
trigger <- input$trigger
}
cars * trigger
}, error=function(cond) {
message("Destroy UI here!")
})
})
# obseveEvent based on the error reactive, to check if hide or not the UI
observeEvent(foo(), {
# hide checking if foo is null, using shinyjs
if (is.null(foo())) {
shinyjs::hide('hideable_div')
} else {
shinyjs::show('hideable_div')
}
}, ignoreNULL = FALSE, ignoreInit = FALSE)
# outputs, with validation of the error reactive. That way code after validate is not
# executed but the app does not get blocked (gray)
output$my_plot <- renderPlot({
shiny::validate(
shiny::need(foo(), 'no data')
)
cars2 <- foo() + rnorm(nrow(foo()))
plot(cars2)
})
}
ui <- fluidPage(
# really important for shinyjs tu work!!!!!!!
shinyjs::useShinyjs(),
my_module_ui("my_id")
)
server <- function(input, output, session) {
callModule(my_module_server, "my_id")
}
shinyApp(ui, server)