为什么我的闪亮应用程序拒绝呈现？

Question

我闪亮的应用程序不起作用，我不知道为什么： 这会尝试获取输入并计算输出并渲染结果 在输出 $mortgagepayment。 当我运行应用程序时，它会给我以下消息：

.getReactiveEnvironment()$currentContext() 中的错误： 如果没有活动的反应上下文，则不允许操作。 （你试图做一些只能在反应式表达式或观察者内部完成的事情。）

library(shiny)

# Define UI ----
ui <- fluidPage(
    titlePanel("Basic widgets"),

     fluidRow(

         # column(3,
         #       h3("Buttons"),
         #        actionButton("action", "Action"),
         #        br(),
         #        br(),
         #        submitButton("Submit")),

         # column(3,
         #        h3("Single checkbox"),
         #        checkboxInput("checkbox", "Choice A", value = TRUE)),

         column(3,
                checkboxGroupInput("Fixed",
                                   h3("Mortgage Year"),
                                   choices = list("30 year" = 30,
                                                  "15 year" = 15,
                                                  "10 year" = 10),
                                   selected = 1)),

         # column(3,
         #       dateInput("date",
         #                 h3("Date input"),
         #                  value = "2014-01-01"))
     ),

    fluidRow(

        # column(3,
        #        dateRangeInput("dates", h3("Date range"))),
        # 
        # column(3,
        #        fileInput("file", h3("File input"))),



        column(3, 
               numericInput("housePrice", 
                            h3("Housing Price"), 
                            value = 1)),   


        column(3, 
               numericInput("percentageDown", 
                            h3("Percentage Down"), 
                            value = 1),min=0,max=1) ,  

        column(3, numericInput("mortgageYield", h3("Mortgage Yield"), value=0.0, min = 0, max = 0.1, step = NA,
                              width = NULL)),
        ),

    fluidRow(
        column(3, h3("Mortgage Payment"), verbatimTextOutput("mortgagepayment")))
)



# Define server logic ----
server <- function(input, output) {
   housePrice = input$housePrice
   downPayment = input$percentageDown    
   mortgageYield = input$mortgageYield 
   mortgageAmount = housePrice*(1-downPayment)
   years = session$fixed
   mortgagePayment = (mortgageAmount*mortgageYield)/(1-1/(1+mortgageYield)^(12*years))
   output$mortgagepayment <-renderText({mortgagePayment})
   }

# Run the app ----
shinyApp(ui = ui, server = server)

Answer 1

有几处需要纠正。

1. 所有对input$... 变量的引用都必须在反应组件内；在这种情况下，它可能会在renderText(...) 内。

2. session$fixed 错了，你的意思可能是input$fixed。

3. 您声明checkboxGroupInput("Fixed",...)（大写“F”）但引用...$fixed（小写“f”），R 区分大小写。

4. 你尝试直接使用复选框的值，但复选框的值是字符串；您需要使用years <- as.numeric(input$fixed)（假设您继续将复选框选择有意义的数字命名为趋势）。

您当前的默认驱动器为 0 的付款（即，percentageDown=1 表示全额为首付，因此无需任何欠款）。

我认为你的服务器组件应该是这样的：

server <- function(input, output) {
  output$mortgagepayment <- renderText({
    # prevent this block from trying to calculate when other fields are
    # empty or invalid
    req(input$housePrice, input$percentageDown, input$mortgageYield, input$Fixed)
    # message("calculate!") # just advises when this block fires
    housePrice = input$housePrice
    downPayment = input$percentageDown    
    mortgageYield = input$mortgageYield 
    mortgageAmount = housePrice*(1-downPayment)
    years = as.numeric(input$Fixed)
    mortgagePayment = (mortgageAmount*mortgageYield)/(1-1/(1+mortgageYield)^(12*years))
    mortgagePayment
  })
}