Make bslib::card_header dynamic

Question

I am building a shiny server module. The UI part is a bslib::card(), like this:

my_mod_ui <- function(id) {
    ns <- shiny::NS(id)
    bslib::card(
        id=id,
        full_screen = TRUE, 

        # the following does not work properly:
        bslib::card_header(paste("Selected: ", shiny::textOutput(ns("selected")))), 

        bslib::layout_sidebar(
            sidebar = bslib::sidebar(
                selectInput(ns("choice"), choices=letters(1:5))
            ), 
            "Main contents"
        )
    )
}

The server part in this minimal example does simply update the selected output variable:

my_mod_srv <- function(id) 
    shiny::moduleServer(id, function(input, output, session) {  
        output$selected <- renderText(input$choice)
})

This code does not work, as the following app shows:

ui <- bslib::page_navbar(
    bslib::nav_panel("Test", my_mod_ui("id1"))
)

server <- function(input, output, session) {
    my_mod_srv("id1")
}

shinyApp(ui, server)

The problem seems to be that output$selected is rendered to an HTML element <div id="id1-selected" class="shiny-text-output"></div>.

How can I make the card header dynamic?

(note that I am using the github version of bslib, the CRAN version does not have a card yet.)

Answer 1

One option would be to move the paste part into renderText:

Note: Assuming that output$wz_title is what you mean by output$selected.

library(bslib)
library(shiny)

my_mod_ui <- function(id) {
  ns <- shiny::NS(id)
  bslib::card(
    id = id,
    full_screen = TRUE,
    bslib::card_header(shiny::textOutput(ns("selected"))),
    bslib::layout_sidebar(
      sidebar = bslib::sidebar(
        selectInput(ns("choice"), "", choices = letters[1:5])
      ),
      "Main contents"
    )
  )
}

my_mod_srv <- function(id) {
  shiny::moduleServer(id, function(input, output, session) {
    output$selected <- renderText(
      paste("Selected: ", input$choice)
    )
  })
}

ui <- bslib::page_navbar(
  bslib::nav_panel("Test", my_mod_ui("id1"))
)

server <- function(input, output, session) {
  my_mod_srv("id1")
}

shinyApp(ui, server)