Stop reactions with isolate()

Ordinarily, the simple act of reading a reactive value is sufficient to set up a relationship, where a change to the reactive value will cause the calling expression to re-execute. The isolate() function allows an expression to read a reactive value without triggering re-execution when its value changes.

In this exercise, you will use the isolate() function to stop reactive flow.

Deze oefening maakt deel uit van de cursus

Building Web Applications with Shiny in R

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Oefeninstructies

Update the server code so that the text output updates only when user changes the height or weight, and NOT the name.

Praktische interactieve oefening

Probeer deze oefening eens door deze voorbeeldcode in te vullen.

ui <- fluidPage(
  titlePanel('BMI Calculator'),
  sidebarLayout(
    sidebarPanel(
      textInput('name', 'Enter your name'),
      numericInput('height', 'Enter your height (in m)', 1.5, 1, 2, step = 0.1),
      numericInput('weight', 'Enter your weight (in Kg)', 60, 45, 120)
    ),
    mainPanel(
      textOutput("bmi")
    )
  )
)

server <- function(input, output, session) {
  rval_bmi <- reactive({
    input$weight/(input$height^2)
  })
  output$bmi <- renderText({
    bmi <- rval_bmi()
    # MODIFY CODE BELOW: 
    # Use isolate to stop output from updating when name changes.
    paste("Hi", input$name, ". Your BMI is", round(bmi, 1))
  })
}

shinyApp(ui = ui, server = server)

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