Hide and Show Download Button Using Shiny Modularity - r

Question

So far I made a Shiny app that has three inputs connected to the database and a final download button. Everything works well except the download button. The actual data downloading part works but I want to add one last logic that hides the download button if myvars$input3 is empty:
observe({
if (is.null(myvars$var3)) {shinyjs::hide("???")}
else {shinyjs::show("???")}
})
server_tab2.R:
Function1 dropdownTab2Server:
Defined the date range logic with id daterange_tab2
Defined the last input dropdown logic with id var_list_tab2
Function2 downloadTab2Server:
Defined the logic for download button
server.R: (This part is not working)
Want to only show the download button if the third input (myvars$input3) is not empty
ui_tab2.R: Defined the three inputs explained in ui.R:
var_lab_tab2: A static dropdown input with only two choices Choice1 and Choice2
daterange_tab2_ui: A date range
subid_dropdown_tab2_ui: The last dropdown input that depends on the first two
##### server_tab2.R
#### Function 1 - A dropdown input dependent on the date range
dropdownTab2Server <- function(id) {
moduleServer(id, function(input, output, session) {
ns <- session$ns
rv <- reactiveValues()
output$daterange_tab2_ui <- renderUI({
req(input$var_lab_tab2)
dateRangeInput(ns("daterange_tab2"), "Date Range:", start = min_max_date_df$min_date, end = min_max_date_df$max_date) # Retrieved from "global.R"
})
unique_lists_tab2 <- reactive({
sql <- glue_sql("
SELECT
DISTINCT list AS unique_list
FROM table1
WHERE date BETWEEN date ({dateid1_tab2*}) AND date ({dateid2_tab2*})
",
dateid1_tab2 = input$daterange_tab2[1],
dateid2_tab2 = input$daterange_tab2[2],
.con = pool
)
dbGetQuery(pool, sql)
})
output$subid_dropdown_tab2_ui <- renderUI({
req(input$daterange_tab2[1], input$daterange_tab2[2])
shinyWidgets::pickerInput(
ns("var_list_tab2"),
"Stations:",
choices = unique_lists_tab2(),
multiple = T
)
})
observe({
rv$var1 <- input$daterange_tab2[1]
rv$var2 <- input$daterange_tab2[2]
rv$var3 <- input$var_list_tab2
})
return(rv)
}
)
}
#### Function 2 - download button
downloadTab2Server <- function(id, df, filename) {
moduleServer(id, function(input, output, session) {
output$downloadbttn_tab2 <- downloadHandler(
filename = function() {
paste0(filename, ".xlsx")
},
content = function(file) {
WriteXLS::WriteXLS(df, file)
}
)
}
)
}
##### server.R => Struggling with this part
function(input, output, session) {
dropdownTab2Server("dropdown_ui_tab2")
myvars <- dropdownTab2Server("dropdown_ui_tab2")
### download button layout => Struggling with this part
observe({
if (is.null(myvars$var3)) {shinyjs::hide("???")}
else {shinyjs::show("???")}
})
downloadTab2Server(
id = "download_ui_tab2",
df = fake_data(), # reactive
filename = "data"
)
}
##### ui_tab2.R
downloadTab2UI <- function(id) {
ns <- NS(id)
tagList(
shinyWidgets::pickerInput(
ns("var_lab_tab2"),
"ID:",
choices = c("Choice1", "Choice2"), multiple = T
),
uiOutput(ns("daterange_tab2_ui")),
uiOutput(ns("subid_dropdown_tab2_ui")),
downloadButton(ns("downloadbttn_tab2"), "Download Data")
)
}
##### ui.R
downloadTab2UI("download_ui_tab2")

Answer 1

You could the following in the main server part (I've changed it to an observeEvent because I think it's easier to reason what exactly it listens to):
observeEvent(myvars$var3, {
if (is.null(myvars$var3)) {shinyjs::hide("download_ui_tab2-downloadbttn_tab2")}
else {shinyjs::show("download_ui_tab2-downloadbttn_tab2")}
}, ignoreNULL = FALSE)
You need to prefix the download button id with the correct namespace, in your case "download_ui_tab2".
However, this is not great style as you need to manually handle the namespace. A cleaner solution would be to pass myvars to the downloadTab2Server module as an argument and then have the observeEvent in the module code. Then you can directly use downloadbttn_tab2 and don't need to manually prefix the namespace.