Ruby on rails 3 Can'；t从Rails引擎中的应用程序控制器访问my helper中的变量

我创建了一个扩展Rails引擎的gem。我使用的是Rails 4。一切正常，除了我无法从助手访问应用程序控制器中的实例变量。这是我的代码…我做错了什么

app/controllers/application\u controller.rb

   class ApplicationController < ActionController::Base

    protect_from_forgery with: :exception

    def get_context
    @variable  = "variable"
    end
    end

      module EvaluateHelper

      def app_name
      @variable   #=> nothing here
      end
      end

      require "rails"
      require "evaluate/version"

     module Evaluate
      VERSION = "0.0.1"

     class Engine < ::Rails::Engine
      end
    end

lib/evaluate/version.rb

   class ApplicationController < ActionController::Base

    protect_from_forgery with: :exception

    def get_context
    @variable  = "variable"
    end
    end

      module EvaluateHelper

      def app_name
      @variable   #=> nothing here
      end
      end

      require "rails"
      require "evaluate/version"

     module Evaluate
      VERSION = "0.0.1"

     class Engine < ::Rails::Engine
      end
    end

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为什么没有答案？