为什么x-editable-rails gem抛出一个错误:未定义的方法`xeditable？'？

我安装了gem x-editable for rails:

# x-editable
gem 'x-editable-rails'

我将方法添加xeditable?到ActionController:

  # Add a helper method to your controllers to indicate if x-editable should be enabled.
  def xeditable?
    true # Or something like current_user.xeditable?
  end

但仍然出现错误:

ActionView::Template::Error (undefined method `xeditable?' for #<#:0x007f9012ee9e78>):
    14: 
    15:     .panel-body
    16:       /a.doc_title.editable id='doc_title_12345' data-name="doc[title]" data-title="Enter doc title" data-type="text" data-url='/docs/12345' href='#doc_title_12345' = doc.title
    17:       = editable doc, :title
    18: 
  app/views/docs/_single_doc_in_accordion.html.slim:17:in `_app_views_docs__single_doc_in_accordion_html_slim__2506304306156466629_70128411437560'
  app/views/docs/index.html.slim:52:in `_app_views_docs_index_html_slim___3263534966956214695_70128384677640'

我应该在哪里定义方法xeditable?以便它开始工作？

这是application_controller.rb:

class ApplicationController < ActionController::Base

  # Prevent CSRF attacks by raising an exception.
  # For APIs, you may want to use :null_session instead.
  protect_from_forgery with: :exception

end

这是application_helper.rb:

module ApplicationHelper
  # Add a helper method to your controllers to indicate if x-editable should be enabled.
  def xeditable?
    true # Or something like current_user.xeditable?
  end
end

现在我得到了新的错误:相同xeditable?,但是can?(方法未定义)