Delay reactions with eventReactive()

Shiny's reactive programming framework is designed such that any changes to inputs automatically updates the outputs that depend on it. In some situations, we might want to explicitly control the trigger that causes the update.

The function eventReactive() is used to compute a reactive value that only updates in response to a specific event.

rval_x <- eventReactive(input$event, {
 # calculations
})

この演習はコースの一部です

Building Web Applications with Shiny in R

コースを見る

演習の手順

Use eventReactive() to delay the execution of computing BMI until the user clicks on the button.

実践的なインタラクティブ演習

このサンプルコードを完成させて、この演習に挑戦してみましょう。

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

server <- function(input, output, session) {
  # MODIFY CODE BELOW: Use eventReactive to delay the execution of the
  # calculation until the user clicks on the show_bmi button (Show BMI)
  rval_bmi <- reactive({
    input$weight/(input$height^2)
  })
  output$bmi <- renderText({
    bmi <- rval_bmi()
    paste("Hi", input$name, ". Your BMI is", round(bmi, 1))
  })
}

shinyApp(ui = ui, server = server)

コードを編集して実行