Save click coordinates

Question

I have a Shiny app where the goal is to send the user's location to a database. The app automatically detects the user's location, and assigns that to input$lat and input$long. The app also has a leaflet map. If the automatically detected location is incorrect, I want the user to be able to click on the map and, if they subsequently click an action button use_click_loc, assign the map click location as their current location.

In my server I have:

#by default, lat_use and lng_use are based upon detected location
lat_use <- input$lat
lng_use <- input$long

RV<-reactiveValues(Clicks=list())

observeEvent(input$map_click, {
  RV$Clicks <- input$map_click
print(RV)
  })

observeEvent(input$use_click_loc, {
   lat_click <- isolate(RV$Clicks$lat)
  lng_click <- isolate(RV$Clicks$lng)
 print(paste0('lat ',lat_click))
 print(paste0('lat ',lng_click))
 lat_use <- lat_click
 lng_use <- lng_click
 
 })

Looking at the console, RV is storing the click lat/long correctly. But when I click the use_click_loc actionbutton, R cannot find RV as an object and the app crashes. I assume this is because I am fuzzy on exactly how reactivity works.

Answer 1

Try this application, it creates a dataframe (simultating you DB) and you add a row every time you click the action button.

You will be able to see it in the console.

library(shiny)
library(leaflet)
library(dplyr)

clicks <- data.frame(lat = numeric(), lng = numeric(), .nonce = numeric())

ui <- fluidPage(
  leafletOutput("map"),
  actionButton("use_clik_loc", "Check loc")
)

server <- function(input, output) {
  output$map <- renderLeaflet(addTiles(leaflet()))

  observeEvent(input$use_clik_loc, {
    last_click <- isolate(as.data.frame(input$map_click))
    clicks <<- clicks |>
      bind_rows(last_click)
    print(clicks)
  })
}

shinyApp(ui, server)