oberveEvent on an action located in another module

Question

In a shiny app, I have 2 modules, in the first one (mod_1_ui) I have filters and an actionButton.
On the module 2, I want to display a plot WHEN button is clicked.

My problem is that, the observeEvent is in module 2 and the button in module 1.
How can I observeEvent an action in 2 differents modules ?

Below is a reproducible example :

mod_1_ui = function(id) {
  ns = NS(id)
  
  fluidRow(
    column(
    width = 3,
    radioButtons(
      ns("dist"),
      "Distribution type:",
      c(
        "Normal" = "norm",
        "Uniform" = "unif",
        "Log-normal" = "lnorm",
        "Exponential" = "exp"
      )
    ),
    actionButton(
      inputId = ns("btn_go"),
      label = "Go !",
      icon = icon("play")
    )
  ),
  
  column(width = 9,
           mod_2_ui(ns("display_plot"))
         )
  )
}


mod_1_server = function(id, r_global) {
  moduleServer(id, function(input, output, session) {
    mod_2_server("display_plot")
    
  })
}




mod_2_ui = function(id) {
  ns = NS(id)

  plotOutput(outputId = ns("plot"))
}


mod_2_server = function(id, r_global) {
  moduleServer(id, function(input, output, session) {
    
    observeEvent(input$btn_go,{
      output$plot <- renderPlot({
        plot(mtcars$mpg)
      })
    })
    
  })
}




ui <- fluidPage(
  mod_1_ui("mod")
)

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

  mod_1_server("mod", r_global = r_global)
}

if (interactive())
  shinyApp(ui, server)

Answer 1

One option would be to use a reactive or a reactiveVal to pass the state of your button as an argument to the module 2 server:

library(shiny)

mod_1_ui <- function(id) {
  ns <- NS(id)

  fluidRow(
    column(
      width = 3,
      radioButtons(
        ns("dist"),
        "Distribution type:",
        c(
          "Normal" = "norm",
          "Uniform" = "unif",
          "Log-normal" = "lnorm",
          "Exponential" = "exp"
        )
      ),
      actionButton(
        inputId = ns("btn_go"),
        label = "Go !",
        icon = icon("play")
      )
    ),
    column(
      width = 9,
      mod_2_ui(ns("display_plot"))
    )
  )
}

mod_1_server <- function(id, r_global) {
  moduleServer(id, function(input, output, session) {
    show <- reactive({
      input$btn_go
    })
    
    mod_2_server("display_plot", show = show)
  })
}

mod_2_ui <- function(id) {
  ns <- NS(id)

  plotOutput(outputId = ns("plot"))
}

mod_2_server = function(id, r_global, show) {
  moduleServer(id, function(input, output, session) {
    
    observeEvent(show(),{
      output$plot <- renderPlot({
        plot(runif(10, runif(10)))
      })
    })
    
  })
}

ui <- fluidPage(
  mod_1_ui("mod")
)

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

  mod_1_server("mod", r_global = r_global)
}

if (interactive()) {
  shinyApp(ui, server)
}