如何在 Shiny 中重置传单点击事件

Question

我正在 Shiny 中构建一个 Leaflet 应用程序，其想法是用户登录以查看可以点击的特定城市的概览。单击这些城市将放大到该特定城市。如下所示的代码可以实现这一点。

我想不通的是，我还想提供一个名为“返回以查看其他城市”的按钮（在选择城市后出现），单击该按钮时，会将地图“重置”回它的原始状态。

但是，当我点击按钮时，我收到以下错误：

警告：UseMethod 中的错误：“元数据”没有适用的方法应用于“NULL”类的对象

在这里，我使用input$map_marker_click 来确定应用程序应该放大哪个城市，我认为部分问题是我无法在单击它后将其设置回其初始状态 NULL。还有其他我想念的方法吗？

library(shiny)
library(leaflet)
library(leaflet.extras)
library(dplyr)

cities <- data.frame(cities = c("London", "Chicago", "New York", "Philadelphia", "Los Angeles"),
                 lng = c(-0.118092, -87.6298, -74.0060, -75.1642, -118.2477),
                 lat = c(51.509865, 41.848, 40.7128, 39.9586, 34.0522),
                 zoom = c(11, 11, 12, 12, 10))

ui <- bootstrapPage(
  tags$style(type = "text/css", "html, body {width:100%;height:100%}"),
  leafletOutput("map", width = "100%", height = "100%"),
  conditionalPanel("isNaN(input.map_marker_click)", uiOutput("controls"))
)

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

  output$map <- renderLeaflet({
    leaflet(cities, width = "100%", height = "100%") %>%
      addProviderTiles("CartoDB.DarkMatter") %>%
      setView(lng = -56, lat = 49.2402, zoom = 4) %>% 
      addPulseMarkers(lng = ~lng, lat = ~lat,
                      label = ~cities,
                      icon = makePulseIcon())
  })

  output$controls <- renderUI({
    req(input$map_marker_click)
    absolutePanel(id = "controls", top = 100, left = 50, 
                    right = "auto", bottom = "auto", width = "auto", height = "auto",
                    actionButton(inputId = "reset", label = "Return to see other cities", class = "btn-primary")
    )
  })

  observeEvent(input$map_marker_click, {
    city_selected <- filter(cities, lat == input$map_marker_click$lat[1])

    leafletProxy("map") %>%
      clearMarkers() %>%
      clearControls() %>%
      setView(lng = city_selected$lng[1], lat = city_selected$lat[1], zoom = city_selected$zoom[1])
  })

#I know the below is wrong, but I don't know what I'm supposed to do to "reset" the map.
  observeEvent(input$reset, {

    leafletProxy("map") %>%
      setView(lng = -56, lat = 49.2402, zoom = 4) %>%
      addPulseMarkers(lng = ~lng, lat = ~lat,
                      label = ~cities,
                      icon = makePulseIcon())
  })
}

shinyApp(ui, server)

Answer 1

另一种基于反应的输出

将地图创建封闭在一个函数中，这样只需一个函数调用就可以更轻松地进行重置，而无需重复代码：

library(shiny)
library(leaflet)
library(leaflet.extras)
library(dplyr)
library(shinyjs) #for hide function

cities <- data.frame(cities = c("London", "Chicago", "New York", "Philadelphia", "Los Angeles"),
                     lng = c(-0.118092, -87.6298, -74.0060, -75.1642, -118.2477),
                     lat = c(51.509865, 41.848, 40.7128, 39.9586, 34.0522),
                     zoom = c(11, 11, 12, 12, 10))

ui <- bootstrapPage(
  useShinyjs(),
  tags$style(type = "text/css", "html, body {width:100%;height:100%}"),
  leafletOutput("map", width = "100%", height = "100%"),
  conditionalPanel("isNaN(input.map_marker_click)", uiOutput("controls"))
)

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

  #creating the first map within a function so that reset becomes easy

  base_map <- function(){
    leaflet(cities, width = "100%", height = "100%") %>%
      addProviderTiles("CartoDB.DarkMatter") %>%
      setView(lng = -56, lat = 49.2402, zoom = 4) %>% 
      addPulseMarkers(lng = ~lng, lat = ~lat,
                      label = ~cities,
                      icon = makePulseIcon())
  }

  # reactiveVal for the map object, and corresponding output object.
  react_map <- reactiveVal(base_map())
  output$map <- renderLeaflet({
    react_map()
  }) 

  output$controls <- renderUI({
    req(input$map_marker_click)
    absolutePanel(id = "controls", top = 100, left = 50, 
                  right = "auto", bottom = "auto", width = "auto", height = "auto",
                  actionButton(inputId = "reset", label = "Return to see other cities", class = "btn-primary")
    )
  })

  observeEvent(input$map_marker_click, {
    city_selected <- filter(cities, lat == input$map_marker_click$lat[1])

    show('controls')

    leafletProxy("map") %>%
      clearMarkers() %>%
      clearControls() %>%
      setView(lng = city_selected$lng[1], lat = city_selected$lat[1], zoom = city_selected$zoom[1])
  })

  # Making the entire map creation inside reactive function makes it easier to reset
  observeEvent(input$reset, {

    #hiding the control button
    hide('controls')

    # resetting the map

    react_map(base_map()) 

  })
}

shinyApp(ui, server)

Answer 2

我需要在最后一次addPulseMarkers() 通话中添加data = cities。

observeEvent(input$reset, {

leafletProxy("map") %>%
  setView(lng = -56, lat = 49.2402, zoom = 4) %>%
  addPulseMarkers(data = cities, lng = ~lng, lat = ~lat,
                  label = ~cities,
                  icon = makePulseIcon())
})