如何在 Shiny 中保存传单地图

Question

继this 问题之后，我希望将传单地图保存并下载为 png 或 jpeg 图像。我有以下代码，但我不断收到错误消息。

ui <- fluidPage(
  leafletOutput("map"),
  downloadButton("dl")
)

server <- function(input, output, session) {
  output$map <- renderLeaflet({
    leaflet() %>% 
      addTiles()
  })

  output$dl <- downloadHandler(
    filename = "map.png",

    content = function(file) {
      mapshot(input[["map"]], file = file)
    }
  )
}

shinyApp(ui = ui, server = server)

我尝试下载（通过单击按钮）时遇到的错误是

Warning: Error in system.file: 'package' must be of length 1
Stack trace (innermost first):
    65: system.file
    64: readLines
    63: paste
    62: yaml.load
    61: yaml::yaml.load_file
    60: getDependency
    59: widget_dependencies
    58: htmltools::attachDependencies
    57: toHTML
    56: <Anonymous>
    55: do.call
    54: mapshot
    53: download$func [#11]
     4: <Anonymous>
     3: do.call
     2: print.shiny.appobj
     1: <Promise>
Error : 'package' must be of length 1

如果您能告诉我如何使用 leafletProxy 来实现此功能，则可以加分。

Answer 1

概述

由于'leaflet' maps 是交互式的，mapview::mapshot() 函数中使用的传单对象也必须是交互式的。考虑到这一点，用户可以在Shiny app 中保存他们的版本的传单地图。

# install necessary packages
install.packages( c( "shiny", "leaflet", "mapview" ) )

# load necessary packages
library( shiny )
library( leaflet )
library( mapview )

ui <- fluidPage(
  leafletOutput( outputId = "map"),
  downloadButton( outputId = "dl")
)

server <- function(input, output, session) {
  
  # Create foundational leaflet map
  # and store it as a reactive expression
  foundational.map <- reactive({
    
    leaflet() %>% # create a leaflet map widget
      
      addTiles( urlTemplate = "https://{s}.tile.openstreetmap.se/hydda/base/{z}/{x}/{y}.png" ) # specify provider tile and type
    
  }) # end of foundational.map()
  
  # render foundational leaflet map
  output$map <- leaflet::renderLeaflet({
    
    # call reactive map
    foundational.map()
    
  }) # end of render leaflet
  
  # store the current user-created version
  # of the Leaflet map for download in 
  # a reactive expression
  user.created.map <- reactive({
    
    # call the foundational Leaflet map
    foundational.map() %>%
      
      # store the view based on UI
      setView( lng = input$map_center$lng
               ,  lat = input$map_center$lat
               , zoom = input$map_zoom
      )
    
  }) # end of creating user.created.map()
  
  
  
  # create the output file name
  # and specify how the download button will take
  # a screenshot - using the mapview::mapshot() function
  # and save as a PDF
  output$dl <- downloadHandler(
    filename = paste0( Sys.Date()
                       , "_customLeafletmap"
                       , ".pdf"
    )
    
    , content = function(file) {
      mapshot( x = user.created.map()
               , file = file
               , cliprect = "viewport" # the clipping rectangle matches the height & width from the viewing port
               , selfcontained = FALSE # when this was not specified, the function for produced a PDF of two pages: one of the leaflet map, the other a blank page.
      )
    } # end of content() function
  ) # end of downloadHandler() function
  
} # end of server

# run the Shiny app
shinyApp(ui = ui, server = server)

# end of script #

最终结果

运行 Shiny 应用后，在新窗口中打开该应用。

进入浏览器后，点击Download。大约需要 3 秒。

单击Download 后，您将立即看到一个PDF 文件，无论您下载的文件存储在计算机上的何处。

参考文献

我的想法来自以下帖子：

• Save leaflet map in Shiny

• How to save a leaflet map in Shiny

• Input/Events - Leaflet for R

• 感谢@blondeclover，使用setView()时无需存储传单地图的bounds。相反，在使用setView() 时只需使用input$MAPID_center$lng 和input$MAPID_center$lat。

  • 要了解有关其他传单输入的更多信息，请参阅list input handlers for a package shiny leaflet。

Answer 2

这可能会有所帮助：

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

    map <- reactiveValues(dat = 0)

      output$map <- renderLeaflet({
        map$dat <- leaflet() %>% 
          addTiles()
      })

      output$dl <- downloadHandler(
        filename = "map.png",

        content = function(file) {
          mapshot(map$dat, file = file)
        }
      )
    }