application_controller.rb

# app/controllers/application_controller.rb

class ApplicationController < ActionController::Base
  before_action :reload_admin, if: :rails_admin_path?

  private

  # implemented in step three  
  def reload_admin; end

  # Returns true if the requested controller contains rails_admin
  # change this as needed if you're using custom controllers
  def rails_admin_path?
    controller_path =~ /rails_admin/ && Rails.env.development?
  end
end