如何在Shiny中创建倒数计时器？

Question

I'd like to be able to create a countdown timer (example: 20 minutes and then the timer beeps) for an R Shiny app that I'm working on that the user can start, stop, and reset by clicking start/stop/reset buttons. I've seen a few examples of countdowns that count towards a specific date/time, but haven't come across one for a generic timer. Is something like this possible? Any help would be appreciated!

Answer 1

这是一种可能的方法。我们使用两个reactiveVal，一个用于跟踪剩余时间，另一个用于存储计时器当前是否处于活动状态。

希望这可以帮助！

library(lubridate)
library(shiny)

ui <- fluidPage(
  hr(),
  actionButton('start','Start'),
  actionButton('stop','Stop'),
  actionButton('reset','Reset'),
  numericInput('seconds','Seconds:',value=10,min=0,max=99999,step=1),
  textOutput('timeleft')

)

server <- function(input, output, session) {

  # Initialize the timer, 10 seconds, not active.
  timer <- reactiveVal(10)
  active <- reactiveVal(FALSE)

  # Output the time left.
  output$timeleft <- renderText({
    paste("Time left: ", seconds_to_period(timer()))
  })

  # observer that invalidates every second. If timer is active, decrease by one.
  observe({
    invalidateLater(1000, session)
    isolate({
      if(active())
      {
        timer(timer()-1)
        if(timer()<1)
        {
          active(FALSE)
          showModal(modalDialog(
            title = "Important message",
            "Countdown completed!"
          ))
        }
      }
    })
  })

  # observers for actionbuttons
  observeEvent(input$start, {active(TRUE)})
  observeEvent(input$stop, {active(FALSE)})
  observeEvent(input$reset, {timer(input$seconds)})

}

shinyApp(ui, server)