Capturing select input in R Shiny? - r

Question

I am trying to capture the url that has been selected when a person presses the "GET URLS" button on the app.
What should happen is that the event reactive() should look at the input$go_button and see that it has been pressed - it should then perform the expression to take the chosen url from the select input- unfortunately it does nothing.
I have tried debugging with browser() but still had no affect.
All i am trying to do is capture the url that has been selected when a person "presses" the "GET URLS" button.
my sample code is below:
library(shiny)
# Use a fluid Bootstrap layout
ui <- fluidPage(
# Give the page a title
titlePanel("testing select"),
# Generate a row with a sidebar
sidebarLayout(
# Define the sidebar with one input
sidebarPanel(
selectInput("url_selection", "select url:",
choices = c(
'/multi-task/',
"/personal-account",
"/paperless"
)
),
actionButton(inputId = "go_button", label = "Get URLS")
),
# Create a spot for the barplot
mainPanel(
textOutput(outputId = "urls_selected_print")
)
)
)
server <- function(input, output) {
url_capture <- reactive({eventReactive(eventExpr = input$go_button,
valueExpr = {
message("capturing url chosen in selectize input")
chosen_url <- input$url_selection
browser()
return(chosen_url)
})
})
}
shinyApp(ui, server)

Answer 1

You can use observeEvent to capture event when go_button has been pressed. You can store the selection in a reactiveVal which can be displayed in your output.
server <- function(input, output) {
rv <- reactiveVal(NULL)
observeEvent(input$go_button, {
message("capturing url chosen in selectize input")
rv(input$url_selection)
})
output$urls_selected_print <- renderText({rv()})
}

Answer 2

Small alternative to Ben's answer (you just have to remove reactive, because eventReactive is already reactive):
server <- function(input, output) {
url_capture <- eventReactive(eventExpr = input$go_button,
valueExpr = {
message("capturing url chosen in selectize input")
chosen_url <- input$url_selection
return(chosen_url)
})
output$urls_selected_print <- renderPrint({
url_capture()
})
}