Leaflet input$MAPID_center returning NULL

Question

I am building a map using Shiny and want to capture the latitude and longitude of the centre of the map in the variables 'lt' and 'ln'. I am using the below code, however, when it is run, I get NULL values for both 'lt' and 'ln'.

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

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

output$map <- renderLeaflet({
    leaflet() %>%
    addProviderTiles(providers$OpenStreetMap) %>%
    setView(lng = 147.842393, lat = -24.000942, zoom = 6) %>% 
    addSearchOSM(options = searchOptions(collapsed = TRUE))
})

observeEvent(input$MAPID_center, {
    lt <- input$MAPID_center$lat
    ln <- input$MAPID_center$lng
})

})

Answer 1

Your MAPID is wrong.

You've defined your map output as output$map. So map is your ID in this case

When you want to "observe" this map, you need to observe input$map_... objects

Here's a working example

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

ui <- fluidPage(
  leaflet::leafletOutput(
    outputId = "map"
  )
)

server <- function(input, output, session){
  
  output$map <- renderLeaflet({
    leaflet() %>%
      addProviderTiles(providers$OpenStreetMap) %>%
      setView(lng = 147.842393, lat = -24.000942, zoom = 6) %>% 
      addSearchOSM(options = searchOptions(collapsed = TRUE))
  })
  
  observeEvent(input$map_center, {
    lt <- input$map_center$lat
    ln <- input$map_center$lng
    
    print(lt); print(ln)
    
  })
  
}

shinyApp(ui, server)