Trick-event-server

Trick-event-server.r

# This part of the code runs on a Shiny server and interacts with the
# user interface shown at the client's side.
# For details and tutorials go to http://shiny.rstudio.com

server <- shinyServer(function(input, output, server) {
  # Make these character strings 'reactive'. That way
  # the output text is automatically update when these
  # values are changed.
  values <- reactiveValues(state = c("Interface1: Waiting for clicks",
                                      "Interface2: Waiting for clicks"))

  # Try to count the number of clicks on each interface. Initialize the counter
  interface <- c(-1, -1)

  # observer for clicks on any of the custom interface elements:
  observeEvent(input$customInterface, {
    # This event observer will always respond to clicks on the second
    # interface, as it's value is negated with each click.
    # We just need to make sure that we take the absolute value of
    # any negated values:
    i <- abs(input$customInterface)

    # count the number of clicks and reset once they have been clicked twice:
    interface[i] <<- (interface[i] + 1)%%2
    if (interface[i] == 0) values$state[i] <- sprintf("Interface%i: click me once, shame on you!", i)
    if (interface[i] == 1) values$state[i] <- sprintf("Interface%i: click me twice, shame on me!", i)
  })

  # render the output text:
  output$outputText <- renderText(paste0(c(values$state[1],
                                           values$state[2]), collapse = "\n"))
})