RShiny反应性错误

Question

我正在构建一个简单的RShiny应用程序来计算样本大小和功率，但我一直收到这个错误消息-警告：.getReactiveEnvironment()$currentContext中的错误:如果没有活动的反应式上下文，则不允许操作。(您尝试做了一些只能从反应式表达式或观察者内部完成的操作。)我想不出怎么解决这个问题。这是我第一次使用RShiny。如果有人能帮上忙，我真的很感激！非常感谢!

library(shiny)
ui <- fluidPage(
headerPanel("Power and Sample Size Calculator"),
fluidRow(column(12,
              wellPanel(
                helpText("Two proportions (equal sample size in each group) power/sample size analysis"),
                selectInput (inputId = "choice",
                             label = " Please Choose What You Want To Calculate",
                             c("Power","Sample Size"),selected = NULL, 
                             multiple = FALSE,
                             selectize = TRUE, width = NULL, size = NULL)
                )),
       column(4,
              wellPanel(
                conditionalPanel(
                  condition = "input$choice = Power",
                  numericInput (inputId = "tau",
                                label = "Effect Size",
                                value = "0.2",
                                min = 0, max =1),
                  numericInput (inputId = "n", 
                                label = "Sample Size in Each Group", 
                                value = "200",
                                min = 0,
                                max = 100000000),
                  sliderInput (inputId = "alpha", 
                               label = "Significance Level ⍺= ", 
                               value = "0.05",
                               min = 0.001, max = 0.10)),
                conditionalPanel(
                  condition = "input$choice=Sample Size",
                  numericInput (inputId = "tau",
                                label = "Effect Size",
                                value = "0.2",
                                min = 0, max =1),
                  sliderInput (inputId = "alpha", 
                               label = "Significance Level ⍺= ", 
                               value = "0.05",
                               min = 0.001, max = 0.10),
                  numericInput (inputId = "beta", 
                                label = "Power", 
                                value = "0.8",
                                min = 0,
                                max = 1))
                )
                ),
       column(8,
              wellPanel(
                htmlOutput("Result")
              ))
              ))


server <- function(input, output) {
choice <- switch (input$choice,
                "Power" = 1, "Sample Size" = 2)
output$Result <- renderUI({
if(choice==1){
  final=reactive({pwr.2p.test(h = input$tau, n = input$n, sig.level = input$alpha, power = )
  })
}
if(choice==2){
  final=reactive({pwr.2p.test(h = input$tau, n = , sig.level = input$alpha, power = input$beta)
})}
HTML(final)
}
)
}

 shinyApp(ui=ui, server=server)