问题
The app below contains an actionButton, a shinyWidgets::progressBar and a selectInput:
When the Start button is clicked, an observeEvent is triggered in which I loop through the numbers 1-10 and increment the progress bar at each iteration. I would also like to update the value of the selectInput at each iteration but updateSelectInput does not work as expected. Instead of updating in tandem with the progress bar, the selectInput value is only updated once the loop has terminated. I don't understand why updateProgressBar works here but updateSelectInput doesn't?
library(shiny)
library(shinyWidgets)
ui <- fluidPage(
actionButton(inputId = "go", label = "Start"), #, onclick = "$('#my-modal').modal().focus();"
shinyWidgets::progressBar(id = "pb", value = 0, display_pct = TRUE),
selectInput('letters', 'choose', letters)
)
server <- function(input, output, session) {
observeEvent(input$go, {
shinyWidgets::updateProgressBar(session = session, id = "pb", value = 0) # reinitialize to 0 if you run the calculation several times
for (i in 1:10) {
updateProgressBar(session = session, id = "pb", value = 100/10*i)
updateSelectInput(session, 'letters', selected = letters[i])
Sys.sleep(.5)
}
})
}
shinyApp(ui = ui, server = server)
回答1:
It works if I set immediate = T in removeUI and insertUI. I got the idea from this post - it doesn't explain why immediate = T is needed though. According to the help page:
Immediate - whether the UI object should be immediately inserted into the app when you call insertUI, or whether Shiny should wait until all outputs have been updated and all observers have been run (default).
But I don't understand what this means in the context of the for-loop. Does it have something to do with the scope of the for-loop?
If someone could post an explanation here I will accept their answer.
Updated code:
library(shiny)
library(shinyWidgets)
ui <- fluidPage(
actionButton(inputId = "go", label = "Start"), #, onclick = "$('#my-modal').modal().focus();"
shinyWidgets::progressBar(id = "pb", value = 0, display_pct = TRUE),
div(id = 'placeholder')
)
server <- function(input, output, session) {
observeEvent(input$go, {
shinyWidgets::updateProgressBar(session = session, id = "pb", value = 0) # reinitialize to 0 if you run the calculation several times
for (i in 1:10) {
updateProgressBar(session = session, id = "pb", value = 100/10*i)
removeUI('#text', immediate = T)
insertUI('#placeholder', ui = tags$p(id = 'text', paste('iteration:', i)), immediate = T)
Sys.sleep(1)
}
})
}
shinyApp(ui = ui, server = server)
来源：https://stackoverflow.com/questions/59799641/r-shiny-updating-the-value-of-a-selectinput-and-progressbar-simultaneously