Leaflet input$MAPID_center returning NULL - r

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)

Answer 2

If you want those variables in the global environment you may use <<- operator.
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
})
}