Observer demo


              

              

              

                In this example, what's visible in the client isn't
                what's interesting. The server is writing to a log
                file each time the slider value changes.
              

            

          

        

        		
      
    

  

  

    

      

        
        

      

      

        

          
            
            show with app
          
          
          

            

              
function(input, output, session) {

  # Create a random name for the log file
  logfilename <- paste0('logfile',
                        floor(runif(1, 1e+05, 1e+06 - 1)),
                        '.txt')


  # This observer adds an entry to the log file every time
  # input$n changes.
  obs <- observe({    
    cat(input$n, '\n', file = logfilename, append = TRUE)
  })


  session$onSessionEnded(function() {
    # When the client ends the session, clean up the log file
    # for this session.
    unlink(logfilename)
  })


  output$text <- renderText({
    paste0("The value of input$n is: ", input$n)
  })

}

            

            

              
fluidPage(
  titlePanel("Observer demo"),
  fluidRow(
    column(4, wellPanel(
      sliderInput("n", "N:",
                  min = 10, max = 1000, value = 200, step = 10)
    )),
    column(8,
      verbatimTextOutput("text"),
      br(),
      br(),
      p("In this example, what's visible in the client isn't",
        "what's interesting. The server is writing to a log",
        "file each time the slider value changes.")
    )
  )
)