问如何在Rails中预览电子邮件？

EN

# located in test/mailers/previews/notifier_mailer_preview.rb

class NotifierPreview < ActionMailer::Preview
  # Accessible from http://localhost:3000/rails/mailers/notifier/welcome
  def welcome
    Notifier.welcome(User.first)
  end
end

#routes.rb

MySite::Application.routes.draw do
  namespace :admin do
    match 'mailer(/:action(/:id(.:format)))' => 'mailer#:action'
  end
end

#app/controllers/admin/mailer_controller.rb
class Admin::MailerController < Admin::ApplicationController

  def preview_welcome()
    @user = User.last
    render :file => 'mailer/welcome.html.erb', :layout => 'mailer'
  end

end