Shiny: How to disable download button when there no data? - r

Question

I'm working inside a module which queries some data and then shows it on a DT::datatable, I added a download button so I can download the data with the filters applied.
I already called useShinyjs() in the main ui file of the app.
But I want to disable the download button in case there is no data.
I've tried the following.
observeEvent(data(), {
if (!nrow(data()) > 0) {
shinyjs::disable("download")
} else {
shinyjs::enable("download")
})
However the next error message shows up, and the app crashes as soon as I run it.
Expecting a single string value: [type=character; extent=0]
ui Code:
module_ui <- function(id) {
ns <- NS(id)
tagList(
fluidRow(
tabBox(
title = tagList(
downloadButton(ns("download"), label = "Download data")
),
width = 12,
tabPanel(
title = HTML("Documentation"),
div(style = 'overflow-x: scroll;font-size:90%', DTOutput(ns("table")))
)
)
)
)
}
server Code:
module_server <- function(id,
connection,
update_button,
update_button_name) {
moduleServer(
id = id,
module = function(input, output, session) {
ns <- session$ns
# 1 . Data -----
data <- eventReactive(list(update_button()), {
data <- dbGetQuery(
connection,
glue::glue("SELECT * FROM Process;)
return(data)
}, ignoreNULL = FALSE, ignoreInit = FALSE)
# 2 . Table -----
output$table<- renderDT({
shiny::validate(
shiny::need(!is_null(data()) && nrow(data()) > 0, 'No data...')
)
datatable(
data = data(),
selection = "single",
style = "bootstrap",
rownames = FALSE,
filter = 'top',
options = list(
searchHighlight = TRUE,
dom = 'tipr',
pageLength = 20,
columnDefs = list(
list(visible = F, targets = c(0)),
list(width = "200px", targets = "_all")
)
)
)
}, server = TRUE)
# 3 . Download -----
observeEvent(data(), {
if (nrow(data()) > 0) {
shinyjs::enable("download")
} else {
shinyjs::disable("download")
}
})
output$download <- downloadHandler(
filename = "Documentation.xlsx",
content = function(file) {
openxlsx::write.xlsx(
x = data() %>% slice(input$tabla_rows_all),
file = file,
asTable = FALSE,
row.names = FALSE
)
}
)
Many thanks in advance to whoever can help!

Answer 1

Use shinyjs::toggleState() instead. Here is a reproducible example:
library(shiny)
library(shinyjs)
ui <- fluidPage(
shinyjs::useShinyjs(),
fileInput(
inputId = "file1", label = "Choose a file to upload:", accept = ".csv"
),
tableOutput(
outputId = "table1"
),
downloadButton(
outputId = "download_data", class = "btn-success"
)
)
server <- function(input, output, session) {
the_data <- reactive({
req(input$file1)
read.csv(input$file1$datapath)
})
output$table1 <- renderTable({
the_data() |> head()
})
# <-- observe if there's any input file -->
observe({
# mandatory condition: there should be an input file
mand_condition <- \() {
!is.null(input$file1)
}
shinyjs::toggleState(
id = "download_data", condition = mand_condition()
)
})
output$download_data <- downloadHandler(
filename = \() {
input$file1$name
},
content = function(file) {
write.csv(the_data(), file)
}
)
}
shinyApp(ui, server)