Leaflet/shiny：无法绘制反应多边形

看完了Leaflet for R 页面上的闪亮集成示例 https://rstudio.github.io/leaflet/shiny.html，我在子集化和显示一些多边形以在我闪亮的应用程序中显示时遇到问题。

目前，我正在得到一个带有侧边栏的应用程序，但主要显示只是“错误：不知道如何从反应类对象获取路径数据”

这个想法是从 GB（3 个国家）中选择一个国家多边形并根据下拉选项单独显示它；

require(shiny)
require(rgdal)
require(rgeos)
require(leaflet)

cont <- readOGR(".\\mypath\\mypolygons.shp", "mypolygons", stringsAsFactors=FALSE)

ui <- fluidPage(

  titlePanel("My page"),

  sidebarLayout(
    sidebarPanel(
      selectInput("countryInput", "Country:", choices = c('England','Scotland','Wales'))
    ),
    mainPanel(
      leafletOutput("mymap")
    )
  )
)

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

pols <- eventReactive(input$countryInput,{cont[substr(cont@data$code,1,1)==substr(input$countryInput,1,1),]})

  output$mymap <- renderLeaflet({
    leaflet() %>%
      addProviderTiles("CartoDB.Positron") %>%
      addPolygons(data = pols)
  })
}


shinyApp(ui, server)

error:

Warning: Error in polygonData.default: Don't know how to get path data from object of class reactive
Stack trace (innermost first):
    83: polygonData.default
    82: polygonData
    81: derivePolygons
    80: addPolygons
    79: function_list[[k]]
    78: withVisible
    77: freduce
    76: _fseq
    75: eval
    74: eval
    73: withVisible
    72: %>%
    71: func [#6]
    70: output$mymap
     4: <Anonymous>
     3: do.call
     2: print.shiny.appobj
     1: <Promise>

fix:

首先我改变了；

pols <- eventReactive(input$countryInput,{cont[substr(cont@data$code,1,1)==substr(input$countryInput,1,1),]})

to;

pols <- reactive({cont.sim[substr(cont.sim@data$gssCode,1,1)==substr(input$countryInput,1,1),]

并且“addPolygons”行在变量名“pols”之后缺少开/闭括号

addPolygons(data = pols)

becomes

addPolygons(data = pols())