How to pass a variable to a layout?

Question

I have a two versions of my application layout, which are differs only in a few lines. Consider following example:

!!!    
%html
    %head
        # a lot of cod         


        

Answer 1

I usually prefer to use helper methods instead of instance variables in these situations. Here is an example of how it could be done:

class ApplicationController < ActionController::Base
  layout 'layout'
  helper_method :flag

  ...

protected
  def flag
    true
  end
end

And if you have a controller where flag should not be true then you just overwrite the method:

class PostsController < ApplicationController
  ...

private
  def flag
    false # or perhaps do some conditional
  end
end

This way you make sure that the flag helper is always available in views so you don't have to do the if defined? or anything and also, in the cases where no layout is used, then no instance variable is assigned in any before_filter.

It also helps keep as few instance variables as possible in the views.