how to make renderText() only trigger by a button Rshiny - r

Question

I have a question when using renderText() function when this text box is triggered by a button. The output Error only triggered by the button for the first time, but for the second or third time, I don't have to click the button, the error text already showed. I think it is really confusing. Here is my code:
library(DT)
shinyServer(function(input, output) {
observeEvent(input$searchbutton, {
if (input$id %in% df$ID) {
data1 <-
datatable({
memberFilter <-
subset(df, df$ID == input$id)
}, rownames = FALSE, options = list(dom = 't'))
output$decision <- DT::renderDataTable({
data1
})
}
else{
output$Error<- renderText(if(input$id %in% df$ID || input$id==""){}
else{
paste("This ID :",input$id,"does not exist")
})
})
}
})
})
so the problem is in this renderText function, if I click the button more than once, the text box will updated automatically when I change the input even i did not click the button.
I guess this issue is because the text box has been triggered, it always 'rendering' the text box, so it did not need to trigger again, if there any solution can make this renderText box always been triggered by button?

Answer 1

It would be better if you could prepare minimal, reproducible example, so we could talk about your real or almost-real app, but I have prepared MRE for our discussion:
library(shiny)
ids <- 1:5
ui <- fluidPage(
numericInput("id_to_check", "Id to check", value = 0),
actionButton("check_id_btn", "Check"),
textOutput("check_result")
)
server <- function(input, output, session) {
observeEvent(input$check_id_btn, {
if (input$id_to_check %in% ids) {
} else {
output$check_result <- renderText({
paste0("This ID: ", input$id_to_check, " does not exist.")
})
}
})
}
shinyApp(ui, server)
So we have ids (from 1 to 5) and the Shiny app, in the server in observeEvent we check if the chosen id (from numericInput) exists in ids and if not, we display the user information that id doesn't exist.
Is this app shows the problem you see in your app? When you push "Check" button (and leave 0 as a id), text is displayed and then, when you change id, text - at least visually - changes and gives wrong results (e.g. if we change id to 1, then we should see any text output according to this part of code:
if (input$id_to_check %in% ids) {
} else {
)
So the first thing is that:
you should never nest objects which belongs to reactive context (observe, reactive, render*),it just won't work in expected way most of the time.
If you want to trigger render* only if the event occurs (like the button is pushed), then you can use bindEvent() function (from shiny):
library(shiny)
ids <- 1:5
ui <- fluidPage(
numericInput("id_to_check", "Id to check", value = 0),
actionButton("check_id_btn", "Check"),
textOutput("check_result")
)
server <- function(input, output, session) {
output$check_result <- renderText({
if (!input$id_to_check %in% ids) {
paste0("This ID: ", input$id_to_check, " does not exist.")
}
}) |>
bindEvent(input$check_id_btn)
}
shinyApp(ui, server)
I have removed observeEvent(), because I don't see the reason to leave it if we want just to display something, but I don't know your app, so maybe you need this, but do not nest anything which is reactive.