我正在开发一个闪亮的仪表板，用户可以在其中发送电子邮件 . 一旦他点击 Send Email 按钮，我想显示用户发送电子邮件的进度 . 目前我正在使用以下代码，首先执行进度条，然后开始发送电子邮件 .

observeEvent(input$send_email, {
final_data <- loadData()
city <- input$city_select
country <- input$country_select
email_type <- input$email_select
start_date <-  format(input$dateRange[1])
end_date <- format(input$dateRange[2])
from <- as.integer(input$from)
to <- as.integer(input$to)

progress <- Progress$new(session, min=1, max=15)
on.exit(progress$close())

progress$set(message = 'Sending Emails',
             detail = 'This may take a while...')

for (i in 1:to) {
  progress$set(value = i)
  Sys.sleep(0.5)
}

email_data <- final_data[final_data$registrant_city == city & (final_data$create_date >= start_date & final_data$create_date <= end_date),]
emails<- quick_email(email_data,city,country)
emails <- emails[from:to]

send_email(emails,input$subject_select)

session$sendCustomMessage(type = 'testmessage',
                          message = paste0('Emails have been successfully sent to ',city,' region,please update the excel sheet.'))


})

send_email 函数将电子邮件发送给所需的收件人 . 我应该在哪里放置进度条代码，以便在电子邮件发送开始后立即启动 .

r shiny