Scheduled Invalidation — invalidateLater

invalidateLater(millis, session = getDefaultReactiveDomain())

Arguments

millis	Approximate milliseconds to wait before invalidating the current reactive context.
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.

Description

Schedules the current reactive context to be invalidated in the given number of milliseconds.

Details

If this is placed within an observer or reactive expression, that object will be invalidated (and re-execute) after the interval has passed. The re-execution will reset the invalidation flag, so in a typical use case, the object will keep re-executing and waiting for the specified interval. It's possible to stop this cycle by adding conditional logic that prevents the invalidateLater from being run.

See also

reactiveTimer() is a slightly less safe alternative.

Examples

## 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, session) {

  observe({
    # Re-execute this reactive expression after 1000 milliseconds
    invalidateLater(1000, session)

    # 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 at timed intervals, but not when
  # input$n changes.
  output$plot <- renderPlot({
    # Re-execute this reactive expression after 2000 milliseconds
    invalidateLater(2000)
    hist(rnorm(isolate(input$n)))
  })
}

shinyApp(ui, server)
}