Code Editor for app.R

library(shiny)

ui <- fluidPage(
  fileInput("file", "Choose a file"),
  selectInput("choice", "Make a choice:", 
              choices = c("Choice A", "Choice B")),
  actionButton("submit", "Submit"),
  tableOutput("filecontents")
)

server <- function(input, output) {
  observeEvent(input$submit, {
    if(input$choice == "Choice A") {
      showModal(modalDialog(
        title = "Warning",
        "You selected Choice A!",
        easyClose = TRUE
      ))
      
      # Only show table if there's a file and Choice A is selected
      output$filecontents <- renderTable({
        req(input$file)
        read.csv(input$file$datapath)
      })
    }
  })
}

shinyApp(ui = ui, server = server)