Shiny应用中R6类私有字段更新后UI无响应问题咨询

Shiny的响应式渲染仅会监听*响应式对象（reactiveVal/reactiveValues）*的变化，你当前把..counter、..desc都定义为普通R6私有字段，修改这些普通变量时，Shiny的渲染函数renderText无法感知到数据更新，因此不会触发UI重绘，这就是UI没有变化的根本原因。

直接将需要响应式更新的变量替换为Shiny的响应式对象即可，无需重构现有R6类的整体结构，修改成本极低。核心修改点如下：

• 把..counter和..desc从普通变量改成reactiveVal类型
• 所有读取这两个值的地方都加()，比如private$..counter()
• 所有修改这两个值的地方用函数赋值写法，比如private$..counter(新值)

完整修改后可运行代码 #

library(R6)
library(stringi)
library(shiny)

df <- data.frame(dp = c("dp1", "dp2", "dp3"), desc = c("problem 1", "problem 2", "problem 3"))

app <- R6::R6Class(classname = "App",
            private = list(
              #unique string id
              ..id = stringi::stri_rand_strings(1, 18),
              #the data to be iterated through
              ..df = df,
              # 将counter改为响应式变量
              ..counter = reactiveVal(1),
              #initiating the dp and desc
              ..dp = 'dp1',
              # 将desc改为响应式变量
              ..desc = reactiveVal('problem 1'),
              
              #the underlying server, to be created like a normal server
              .server = function(input, output, session){
                output$text <- renderText({ 
                  # 响应式变量取值加()
                  private$..desc()
                })
                
                observeEvent(input$button, {
                  # 响应式变量赋值用函数写法
                  private$..counter(private$..counter() + 1)
                  self$update_private()
                  #check the private content since the print is not updating
                  print(private$..counter())
                  print(private$..dp)
                  print(private$..desc())
                })
              }
            ),
            public = list(
              #create names for ui elements
              button = NULL,
              text = NULL,
              initialize = function(){
                
                self$button <- self$get_id("button")
                self$text <- self$get_id("text")
                self$update_private()
              },
              
              #gives ui outputs unique names tied to the user's id
              get_id = function(name, ns = NS(NULL)){
                ns <- NS(ns(private$..id))
                id <- ns(name)
                return(id)
              },
              #automatically updates the private field based on the counter
              update_private = function(){
                counter_val <- private$..counter()
                if(counter_val == 1){
                  private$..dp <- "dp1"
                } else if(counter_val == 2){
                  private$..dp <- "dp2"
                } else{
                  private$..dp <- "dp3"
                }
                # 更新desc响应式变量的值
                private$..desc(private$..df[private$..df$dp == private$..dp, "desc"])
              },
              
              ui = function(){
                fluidPage(
                  h1("An Example"),
                  mainPanel(
                  textOutput(self$text)),
                  sidebarPanel(
                  shiny::actionButton(inputId = self$button, 
                                      label = 'Update!', 
                                      width = '100%'
                  ))
                  

                )
              },#end ui
              
              server = function(input, output, session){
                callModule(module = private$.server, id = private$..id)
              }
            )
)

test <- app$new()

ui <- test$ui()

server <- function(input, output, session) {
  test$server()
}
shinyApp(ui = ui, server = server)

内容的提问来源于stack exchange，提问作者mauraeh