display of 'sync' (mapview) in shiny

Question

I’m trying to have two spatial plots side-by-side in shiny, and I was suggested a powerful function, sync of mapview. After figuring how to display mapview object in shiny, I tried to integrate sync in 'shiny', but got the following error: Error in slot(x, "map") : no slot of name "map" for this object of class "shiny.tag.list" . Does it mean sync does not have map object, therefore, it is not possible to integrate sync or latticeView with shiny? If so, I guess there should be workaround solutions and my ears are all open. This is a nice feature to have access from Shiny and allows to do some interesting things. Greatly appreciate any suggestions. Here is the sample reproducible code:

library(shiny)
library(mapview)
ui <- fluidPage(
   mapviewOutput("samplemap"),
   p()
)
server <- function(input, output, session) {
   output$samplemap <- renderMapview({
      m1 <- mapview(gadmCHE,zcol="ID_1")
      m2 <- mapview(gadmCHE,zcol="OBJECTID")
      sync(m1,m2)
      })
}
shinyApp(ui, server)

Answer 1

We have discussed making the return value from sync an htmlwidget. Currently, sync returns a htmltools::tagList of the leaflet maps. Inserting tags into shiny will be a little different than inserting mapview. I'll try to explain in code below.

library(mapview)

m1 <- mapview(gadmCHE,zcol="ID_1")
s1 <- sync(m1,m1)


library(shiny)

# if not dynamically adding maps
#   we can just insert as ui

shinyApp(
  ui = s1,
  server = function(input,output){}
)

# if there is a need to create the maps after UI
#   then we will need to handle differently
#   since sync gives us tags instead of an htmlwidget
shinyApp(
  ui = uiOutput("syncmap"),
  server = function(input,output){
    output$syncmap = renderUI({
      s1
    })
  }
)