如何将R闪亮UI中的输入打印到控制台？

Question

情境：我想将R闪亮UI中的输入变量打印到控制台。这是我的代码：

library(shiny)

ui=fluidPage(
  selectInput('selecter', "Choose ONE Item", choices = c("small","big"))
)

server=function(input,output,session){
  print("You have chosen:")
  print(input$selecter)
 }

shinyApp(ui, server)

不幸的是我收到此错误消息：

Error in .getReactiveEnvironment()$currentContext() : 
  Operation not allowed without an active reactive context. (You tried to do something that can only be done from inside a reactive expression or observer.)

问题：我需要将代码更改为什么才能使其正常工作？

Answer 1

您应该使用observeEvent，每次输入更改时都会执行：

library("shiny")

ui <- fluidPage(
    selectInput('selecter', "Choose ONE Item", choices = c("small","big")),
    verbatimTextOutput("value")  
)

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

  observeEvent(input$selecter, {
    print(paste0("You have chosen: ", input$selecter))
  })

}

shinyApp(ui, server)