r - 操作按钮和observeEvent

Question

我想要一个按钮来触发对预先指定的非 react 变量的操作 x 。每次按下按钮 x <- x + 1应予执行。为了检查是否正确完成，应显示结果。为了实现这一目标，我尝试了 observeEvent() 。但它只做了一次它应该做的事情。它如何正常工作？

看来rv仅在observeEvent()内可用功能。如果output$text_2 <- renderText({ rv$a })放置在 observeEvent() 之外发生错误。我如何使用 observeEvent() 内完成的内容外面？

library(shiny)
x  <- 0

ui <- fluidPage(

  actionButton(inputId = "action", 
               label = "action"),
  textOutput("text_1"),
  textOutput("text_2")

)

server <- function(input, output) {

  output$text_1<- renderText({ input$action })

  observeEvent(input$action, {
               x  <- x + 1 
               rv <- reactiveValues(a = x)
               output$text_2 <- renderText({ rv$a })
               })
}

shinyApp(ui = ui, server = server)

Answer 1

Daattalis 的答案很准确，但我想我可以发布一些示例来说明如何使用 Shinys react 值来做到这一点。

library(shiny)

ui <- fluidPage(

  actionButton(inputId = "action", 
               label = "action"),
  textOutput("txt_example1"),
  textOutput("txt_example2"),
  textOutput("txt_example3")

)

server <- function(input, output) {

  # ------------------ Example 1 ------------------
  #  Use a list of reactive values
  rv <- reactiveValues(x=0)

  # Will update text output when rv$x is updated
  observe({
    output$txt_example1 <- renderText({ rv$x })
  })


  # ------------------ Example 2 ------------------
  #   Make variable a reactive
  x <- 0
  makeReactiveBinding('x')

  # The only 'trick' here is that x is made a reactive so that the observer is
  # triggered every time x is updated.
  # If x is not made a reactive the value of x will still be updated but the observer
  # wont trigger (see example 3).

  observe({
    output$txt_example2 <- renderText({ x })
  })

  # ------------------ Example 3 ------------------
  #   Use ordinary R scoping

  x2 <- 0 

  printUpdate <- function(){
    output$txt_example3 <- renderText({ x2 })
  }

  printUpdate() # Print first value

  # onClick listener, same for all examples
  observeEvent(input$action, {
    rv$x  <- rv$x + 1 # Example 1, update reactive list
    x     <<- x + 1   # Example 2, Save x to parent enviroment

    # Example 3
    x2 <<- x2 + 1     # Again, save x2 to parent enviroment, see help('<<-') 
    printUpdate()     # Update textOutput
  })


}

shinyApp(ui = ui, server = server)

希望这有帮助!