Hide and clear selectInput - r

Question

I need to show\hide input and will be great get NULL or empty string if the input not exists, here reproducible example:
ui <-
dashboardPage(
dashboardHeader(
title = 'Test'),
dashboardSidebar(),
dashboardBody(
selectInput(
inputId = 'mainInput',
label = 'Main input',
selected = 'Show',
choices = c('Show', 'Hide')
),
uiOutput(
outputId = 'secondInputUI'
),
actionButton(
inputId = 'thirdInput',
label = 'Check value'
)
)
)
server <- function(input, output, session){
observeEvent(input$mainInput, ignoreNULL = TRUE, {
if (input$mainInput == 'Show')
output$secondInputUI <-
renderUI(
selectInput(
inputId = 'secondInput',
label = 'Second input',
selected = 0,
multiple = FALSE,
choices = c(1, 0)
)
)
else {
output$secondInputUI <-
renderUI(
selectInput(
inputId = 'secondInput',
label = 'Second input',
selected = '',
multiple = TRUE,
choices = c(1, 0)
)
)
# If uncommit - input value don't update and will return latest available before delete input
# output$secondInputUI <-
# NULL
}
})
observeEvent(input$thirdInput, {
showNotification(
session = session,
ui = paste(input$secondInput, collapse = ', '))
})
}
shinyApp(
ui = ui,
server = server)
You can see commented part with setting NULL to uioutput, if it active - shiny return latest available value before clear that ui, so how to deal with that?

Answer 1

I think I understand. You could create a reactive variable that is independent of the UI, because inputs are not updated when the UI element is removed.
library(shiny)
library(shinydashboard)
ui <-
dashboardPage(
dashboardHeader(
title = 'Test'),
dashboardSidebar(),
dashboardBody(
selectInput(
inputId = 'mainInput',
label = 'Main input',
selected = 'Show',
choices = c('Show', 'Hide')
),
uiOutput(
outputId = 'secondInputUI'
),
actionButton(
inputId = 'thirdInput',
label = 'Check value'
)
)
)
server <- function(input, output, session){
secondInputVar <- reactive({
if(input$mainInput == 'Show'){
input$secondInput
} else {
}
})
observeEvent(input$mainInput, ignoreNULL = TRUE, {
if (input$mainInput == 'Show')
output$secondInputUI <-
renderUI(
selectInput(
inputId = 'secondInput',
label = 'Second input',
selected = 0,
multiple = FALSE,
choices = c(1, 0)
)
)
else {
output$secondInputUI <- renderUI({
NULL
})
}
})
observeEvent(input$thirdInput, {
showNotification(
session = session,
ui = paste(secondInputVar(), collapse = ', '))
})
}
shinyApp(
ui = ui,
server = server)

Answer 2

So, I found another solution, the main idea is: update input value in observer for first input, hide second input from observer for the second input. Will be better if I show:
ui <-
dashboardPage(
dashboardHeader(
title = 'Test'),
dashboardSidebar(),
dashboardBody(
selectInput(
inputId = 'mainInput',
label = 'Main input',
selected = 'Show',
choices = c('Show', 'Hide')
),
uiOutput(
outputId = 'secondInputUI'
),
actionButton(
inputId = 'thirdInput',
label = 'Check value'
)
)
)
server <- function(input, output, session){
observeEvent(input$mainInput, {
if (input$mainInput == 'Show')
output$secondInputUI <-
renderUI(
selectInput(
inputId = 'secondInput',
label = 'Second input',
selected = 0,
multiple = FALSE,
choices = c(1, 0)
)
)
else {
output$secondInputUI <-
renderUI(
selectInput(
inputId = 'secondInput',
label = 'Second input',
selected = '',
multiple = TRUE,
choices = c(1, 0)
)
)
}
})
# THE TRICK HERE ####
observeEvent(input$secondInput, ignoreNULL = FALSE, {
if (input$mainInput != 'Show'){
output$secondInputUI <-
renderUI(NULL)
}
})
observeEvent(input$thirdInput, {
showNotification(
session = session,
ui = paste(input$secondInput, collapse = ', '))
})
}
shinyApp(
ui = ui,
server = server)