reactiveTimer: Timer

Description

Creates a reactive timer with the given interval. A reactive timer is like a reactive value, except reactive values are triggered when they are set, while reactive timers are triggered simply by the passage of time.

Usage

reactiveTimer(intervalMs = 1000, session = getDefaultReactiveDomain())

Value

A no-parameter function that can be called from a reactive context, in order to cause that context to be invalidated the next time the timer interval elapses. Calling the returned function also happens to yield the current time (as in base::Sys.time()).

Arguments

intervalMs: How often to fire, in milliseconds
session: A session object. This is needed to cancel any scheduled invalidations after a user has ended the session. If NULL, then this invalidation will not be tied to any session, and so it will still occur.

Details

Reactive expressions and observers that want to be invalidated by the timer need to call the timer function that reactiveTimer returns, even if the current time value is not actually needed.

See invalidateLater() as a safer and simpler alternative.

Examples

Run this code

## Only run examples in interactive R sessions
if (interactive()) {

ui <- fluidPage(
  sliderInput("n", "Number of observations", 2, 1000, 500),
  plotOutput("plot")
)

server <- function(input, output) {

  # Anything that calls autoInvalidate will automatically invalidate
  # every 2 seconds.
  autoInvalidate <- reactiveTimer(2000)

  observe({
    # Invalidate and re-execute this reactive expression every time the
    # timer fires.
    autoInvalidate()

    # Do something each time this is invalidated.
    # The isolate() makes this observer _not_ get invalidated and re-executed
    # when input$n changes.
    print(paste("The value of input$n is", isolate(input$n)))
  })

  # Generate a new histogram each time the timer fires, but not when
  # input$n changes.
  output$plot <- renderPlot({
    autoInvalidate()
    hist(rnorm(isolate(input$n)))
  })
}

shinyApp(ui, server)
}