fire_event: Fire or read a session event

In shidashi: A Shiny Dashboard Template Modular System with Chat Bot Support

Fire or read a session event

Description

fire_event sets a reactive event value on the current session. When global = TRUE, the event is propagated to all sessions that share the same shared_id (i.e. other browser tabs for the same user).

get_event reads the current value of an event key from the session registry.

get_theme is a convenience wrapper around get_event("theme.changed") that returns the current dashboard theme.

All three functions must be called inside a Shiny server context.

Usage

fire_event(
  key,
  value,
  session = shiny::getDefaultReactiveDomain(),
  global = FALSE
)

get_event(key, session = shiny::getDefaultReactiveDomain(), default = NULL)

get_theme(session = shiny::getDefaultReactiveDomain())

Arguments

key	a single character string identifying the event type
value	the event payload (any R object)
session	a Shiny session (defaults to the current reactive domain)
global	logical; if TRUE, the event is broadcast to all sessions sharing the same shared_id
default	value to return when the event has not been fired yet (used by get_event only)

Details

get_theme and get_event auto-register the session if needed and must be called inside a reactive context (observe, observeEvent, reactive, render functions).

Value

fire_event returns NULL invisibly. get_event returns the last value fired for key, or default if none. get_theme returns a named list with three character elements:

theme

Either "light" or "dark".

foreground

Hex color string for text / foreground elements.

background

Hex color string for the page background.

Before the browser fires its first theme event, the light-theme fallback list(theme = "light", background = "#FFFFFF", foreground = "#000000") is returned.

Examples

library(shiny)
server <- function(input, output, session) {
  # fire an event
  shidashi::fire_event("my_event", list(a = 1), session = session)

  # read it back
  observe({
    evt <- shidashi::get_event("my_event", session = session)
    print(evt)
  })

  # get_theme must be called within a reactive context
  output$plot <- renderPlot({
    theme <- shidashi::get_theme()
    par(bg = theme$background, fg = theme$foreground)
    plot(1:10)
  })
}

shidashi documentation built on April 10, 2026, 5:07 p.m.