R Shiny：使用后退操作按钮转到上一个条件面板

我正在尝试使用操作按钮返回上一个条件面板。到目前为止，我已经编写了以下代码来浏览一系列条件面板，但我无法返回到之前的情况，因为我无法更新输入值，它给了我以下错误：

警告：$

代码如下：

ui.R

shinyUI(
  fluidPage(
    conditionalPanel(
      condition <- "typeof input.link_click  === 'undefined'",
      leafletOutput("Map", width = 1000, height = 500)

    ),


    conditionalPanel(
      condition <- "typeof input.link_click_Site  === 'undefined' && typeof input.link_click  !== 'undefined'",


      leafletOutput("CountryMap", width = 1000, height = 500)

    ),
    conditionalPanel(
      condition <- "typeof input.link_click_Site  !== 'undefined'",

      h3("Plots related to site chosen"),
      textOutput(outputId = "Check"),
      actionButton("Back", "Back")
    )
  )  
)

server.R

library(shiny)
library(leaflet)
library(maps)

shinyServer(function(input, output, session) {

Country = map("world", fill = TRUE, plot = FALSE, regions="USA")
output$Map <- renderLeaflet({
  leaflet(Country) %>% addTiles() %>%  setView(0, 0,  zoom = 2)%>%
    #leaflet(target) %>% addTiles() %>%
    addPolygons(fillOpacity = 0.6,
                fillColor = 'blue',
                smoothFactor = 0.5, stroke = TRUE, weight = 1, popup =  paste("<b>", "USA", "</b><br>",
                                                                              actionLink(inputId = "View", 
                                                                                         label = "View Details", 
                                                                                         onclick = 'Shiny.onInputChange(\"link_click\",  Math.random())')))
})

output$CountryMap <- renderLeaflet({

  leaflet(Country) %>% addTiles() %>%   
    fitBounds(Country$range[1], Country$range[3], Country$range[2], Country$range[4])%>%
    addMarkers(lng = -71.03 , lat = 42.37, popup = paste("<b>", "Boston", "</b><br>",
                                                         actionLink(inputId = "View", 
                                                                    label = "View Details", 
                                                                    onclick = 'Shiny.onInputChange(\"link_click_Site\",  Math.random())')))
})


observeEvent(input$link_click_Site, {
  output$Check <- renderText("Success")

})

observeEvent(input$Back, {
  input$link_click_Site <- 0
})

})

我建议您向输入值添加一个类型，您的conditionalPanels正在测试，您可以控制。

您当前正在检查输入是否link_click and link_click_Site are undefined。一旦设置完毕，您可以使用以下命令重置它们customMessageHandler，但当然不是undefined。我会选择另一个独特的值，例如 JavaScriptnull.

所以基本上将所有条件更改为未定义或为空或类似地不是未定义且不为空。然后您可以通过将它们设置为来重置输入null.

参见下面的代码：

library(shiny)
library(leaflet)    
library(maps)

ui <- shinyUI(
  fluidPage(
    tags$script("
      Shiny.addCustomMessageHandler('resetInputValue', function(variableName){
        Shiny.onInputChange(variableName, null);
      });
    "),

    conditionalPanel(
      condition <- "input.link_click  === undefined || input.link_click === null",
      leafletOutput("Map", width = 1000, height = 500)

    ),


    conditionalPanel(
      condition <- "(input.link_click_Site  === undefined || input.link_click_Site === null) && (input.link_click  !== undefined && input.link_click !== null)",


      leafletOutput("CountryMap", width = 1000, height = 500)

    ),
    conditionalPanel(
      condition <- "(input.link_click_Site  !== undefined && input.link_click_Site !== null)",

      h3("Plots related to site chosen"),
      textOutput(outputId = "Check"),
      actionButton("Back", "Back")
    )
  )  
)

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

  Country = map("world", fill = TRUE, plot = FALSE, regions="USA")
  output$Map <- renderLeaflet({
    leaflet(Country) %>% addTiles() %>%  setView(0, 0,  zoom = 2)%>%
      #leaflet(target) %>% addTiles() %>%
      addPolygons(fillOpacity = 0.6,
                  fillColor = 'blue',
                  smoothFactor = 0.5, stroke = TRUE, weight = 1, popup =  paste("<b>", "USA", "</b><br>",
                                                                                actionLink(inputId = "View", 
                                                                                           label = "View Details", 
                                                                                           onclick = 'Shiny.onInputChange(\"link_click\",  Math.random())')))
  })

  output$CountryMap <- renderLeaflet({

    leaflet(Country) %>% addTiles() %>%   
      fitBounds(Country$range[1], Country$range[3], Country$range[2], Country$range[4])%>%
      addMarkers(lng = -71.03 , lat = 42.37, popup = paste("<b>", "Boston", "</b><br>",
                                                         actionLink(inputId = "View", 
                                                                    label = "View Details", 
                                                                    onclick = 'Shiny.onInputChange(\"link_click_Site\",  Math.random())')))
  })


  observeEvent(input$link_click_Site, {
    output$Check <- renderText("Success")

  })

  observeEvent(input$Back, {
    session$sendCustomMessage(type = 'resetInputValue', message = "link_click_Site")
    session$sendCustomMessage(type = 'resetInputValue', message = "link_click")
  })
}

shinyApp(ui, server)