conditionalPanel 和 uiOutput/req 模式之间的区别

Question

Consider the below sample application demonstrating two ways to show UI based on a condition:

library(shiny)

ui <- fluidPage(
  tagList(
    checkboxInput("toggle", "Toggle"),
    conditionalPanel(
      condition = "output.condition",
      tags$p("Output from conditionalPanel")
    ),
    uiOutput("ui")
  )
)

server <- function(input, output, session) {
        
  # conditionalPanel
  output$condition <- reactive(input$toggle)
  outputOptions(output, "condition", suspendWhenHidden = FALSE)
  
  # uiOutput
  output$ui <- renderUI({
    req(isTRUE(input$toggle))
    tags$p("Output from uiOutput")
  })
  
}

shinyApp(ui, server)

In terms of the front-end, the conditionalPanel and uiOutput / req patterns seem to behave similarly. Are there any differences, especially related to performance, that would make one pattern more beneficial?

Answer 1

These two ways do have different purposes . conditionalPanel creates a JavaScript expression which "listens" for a specific condition, eg whether an input is TRUE or FALSE . Nothing needs to happen on the server-side.

renderUI() in contrast is very flexible. Of course, it can mimic the behavior of conditionalPanel but is also capable to output basically anything by creating different HTML (UI) code.

Regarding speed: conditionalPanel should almost always be faster. Additionally, not performance should be the decider between both options but the goal should.

example app

library(shiny)

ui <- fluidPage(
  tagList(
    checkboxInput("toggle", "Toggle"),
    conditionalPanel(
      # listens whether toggle is TRUE or FALSE
      condition = "input.toggle",
      tags$p("Output from conditionalPanel")
    ),
    uiOutput("ui")
  )
)

server <- function(input, output, session) {

  # create a plot
  output$myplot <- renderPlot({
    plot(mtcars$mpg, mtcars$cyl)
  })

  # create some text
  output$mytext <- renderText({
    "I am pointless"
  })


  # uiOutput
  output$ui <- renderUI({
    input$toggle
    if (rnorm(1) > 0){
      plotOutput("myplot")
    } else {
      textOutput("mytext")
    }
  })

}

shinyApp(ui, server)