这是一种利用我前面的答案的方法。
下面的代码阻止了modalDialog的显示，直到模态被（重新）呈现：

library(shiny)

showMyModal <- function() {
  showModal(
    conditionalPanel("input.modal_visible == true",
                     modalDialog(
                       verbatimTextOutput("mytext"),
                       footer = tagList(
                         modalButton("Dismiss"),
                       )
                     )
    )
  )
}

ui <- fluidPage(
  tags$script(HTML(
    "$(document).on('shown.bs.modal','#shiny-modal', function () {
       Shiny.setInputValue(id = 'modal_visible', value = true);
      });
     $(document).on('hidden.bs.modal','#shiny-modal', function () {
       Shiny.setInputValue(id = 'modal_visible', value = false);
     });"
  )),
  actionButton("openDialog", "Open dialog")
)

server <- function(input, output, session) {
  observeEvent(input$openDialog, {
    showMyModal()
  })
  
  output$mytext <- renderPrint({
    input$openDialog
  })
}

shinyApp(ui = ui, server = server)