“undefined method” when calling helper method from controller in Rails

问题

Does anyone know why I get

undefined method `my_method' for #<MyController:0x1043a7410>

when I call my_method("string") from within my ApplicationController subclass? My controller looks like

class MyController < ApplicationController
  def show
    @value = my_method(params[:string])
  end
end

and my helper

module ApplicationHelper
  def my_method(string)
    return string
  end
end

and finally, ApplicationController

class ApplicationController < ActionController::Base
  after_filter :set_content_type
  helper :all
  helper_method :current_user_session, :current_user
  filter_parameter_logging :password
  protect_from_forgery # See ActionController::RequestForgeryProtection for details

回答1:

You cannot call helpers from controllers. Your best bet is to create the method in ApplicationController if it needs to be used in multiple controllers.

EDIT: to be clear, I think a lot of the confusion (correct me if I'm wrong) stems from the helper :all call. helper :all really just includes all of your helpers for use under any controller on the view side. In much earlier versions of Rails, the namespacing of the helpers determined which controllers' views could use the helpers.

I hope this helps.

回答2:

view_context is your friend, http://apidock.com/rails/AbstractController/Rendering/view_context

if you wanna share methods between controller and view you have further options:

use view_context
define it in the controller and make available in view by the helper_method class method http://apidock.com/rails/ActionController/Helpers/ClassMethods/helper_method
define it in a shared module and include/extend

回答3:

Include ApplicationHelper in application_controller.rb file like this:

class ApplicationController < ActionController::Base
  protect_from_forgery       
  include ApplicationHelper  
end

This way all the methods defined in application_helper.rb file will be available in the controller.

You can also include individual helpers in individual controllers.

回答4:

Maybe I'm wrong, but aren't the helpers just for views? Usually if you need a function in a controller, you put it into ApplicationController as every function there is available in its childclasses.

回答5:

As said by gamecreature in this post:

In Rails 2 use the @template variable.
In Rails 3 use the controller method view_context

回答6:

helpers are for views, but adding a line of code to include that helper file in ApplicationController.rb can take care of your problem. in your case, insert the following line in ApplicationController.rb:

include ApplicationHelper

回答7:

As far as i know, helper :all makes the helpers available in the views...

回答8:

Try appending module_function(*instance_methods) in your helper modules, after which you could directly call those methods on the module itself.

回答9:

though its not a good practice to call helpers in controller since helpers are meant to be used at views the best way to use the helpers in controller is to make a helper method in application_controller and call them to the controller,
but even if it is required to call the helper in a controller
then Just include the helper in the controller

class ControllerName < ApplicationController
  include HelperName
  ...callback statements..

and call the helper methods directly to the controller

 module OffersHelper
  def generate_qr_code(text)
    require 'barby'
    require 'barby/barcode'
    require 'barby/barcode/qr_code'
    require 'barby/outputter/png_outputter'
    barcode = Barby::QrCode.new(text, level: :q, size: 5)
    base64_output = Base64.encode64(barcode.to_png({ xdim: 5 }))
    "data:image/png;base64,#{base64_output}"
  end

Controller

class ControllerName < ApplicationController
include OffersHelper

def new
  generate_qr_code('Example Text')
end
end

hope this helps !

回答10:

I had the same problem...

you can hack/bodge around it, put that logic into a model, or make a class specially for it. Models are accessible to controllers, unlike those pesky helper methods.

Here is my "rag.rb" model

class Rag < ActiveRecord::Base
  belongs_to :report
  def miaow()
    cat = "catattack"
  end  
end

Here is part of my "rags_controller.rb" controller

def update
  @rag = Rag.find(params[:id])
  puts @rag.miaow()
  ...

This gave a catattack on the terminal, after I clicked "update".

Given an instantiation, methods in the model can be called. Replace catattack with some codes. (This is the best I have so far)

:helper all only opens helpers up to views.

This shows how to make a class and call it. http://railscasts.com/episodes/101-refactoring-out-helper-object?autoplay=true

回答11:

Try this to access helper function directly from your controllers view_context.helper_name

来源：https://stackoverflow.com/questions/2388932/undefined-method-when-calling-helper-method-from-controller-in-rails

标签

ruby-on-rails

helper

helpers

applicationcontroller