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$event, {
# calculations
})
This exercise is part of the course
Building Web Applications with Shiny in R
Exercise instructions
- Use
eventReactive()
to delay the execution of computing BMI until the user clicks on the button.
Hands-on interactive exercise
Have a go at this exercise by completing this sample code.
ui <- fluidPage(
titlePanel('BMI Calculator'),
sidebarLayout(
sidebarPanel(
textInput('name', 'Enter your name'),
numericInput('height', 'Enter height (in m)', 1.5, 1, 2, step = 0.1),
numericInput('weight', 'Enter weight (in Kg)', 60, 45, 120),
actionButton("show_bmi", "Show BMI")
),
mainPanel(
textOutput("bmi")
)
)
)
server <- function(input, output, session) {
# MODIFY CODE BELOW: Use eventReactive to delay the execution of the
# calculation until the user clicks on the show_bmi button (Show BMI)
rval_bmi <- reactive({
input$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)