嗨，我需要一个 Jmeter 板页脚的可见性是一些数字的条件。 这段代码很好，只是参数fixed = TRUE`（来自bs4DashFooter）不起作用。

library(shiny)
library(bs4Dash)
library(reactable)

ui = dashboardPage(
  header = dashboardHeader(),
  sidebar = dashboardSidebar(
    sidebarMenu(id = "mmm",
                menuItem("Dashboard Tab 1", tabName = "tab1"),
                menuItem("Dashboard Tab 2", tabName = "tab2")
    )),

  footer = uiOutput("f"),
  
    body = dashboardBody(
    tabItems( 
      tabItem(
        tabName = "tab1",
        h6(("tab 1 content"), style="text-align: center;"),
        reactableOutput(outputId = "t")),
      tabItem(
        tabName = "tab2",
        h6("tab 2 content"), style="text-align: center;")
    )
  )
)
server = function(input, output, session) {
  a <- reactiveValues(q = 3)
  output$f <- renderUI({
    if (as.numeric(isolate(reactiveValuesToList(a)))[1] > 2){
    bs4DashFooter(
      right = "some foot",
      fixed = TRUE)
    }
  })
  
  output$t <- renderReactable({
    reactable(mtcars,
              defaultPageSize = 50)})
}
shinyApp(ui, server)

有人能帮忙吗