Returning mobile views from rails, either by using a custom view path ("views_mobile") or by setting a custom request format.

application_controller.rb

class ApplicationController < ActionController::Base
  before_filter :prepend_view_path_if_mobile
  
  def mobile_request?
    @mobile_request ||= (request.subdomains.first == domain_prefixes[:mobile])
  end
  helper_method :mobile_request?
    
  def prepend_view_path_if_mobile
    prepend_view_path Rails.root + 'app' + 'views_mobile' if mobile_request?
  end
  
  # use this as a before_filter if you want to load a custom template using the [action].mobile.erb naming convention
  # by default we use the prepend_view_path to load the files from the views_mobile path instead or using the format parameter
  def prepare_for_mobile
    request.format = :mobile if mobile_request?
  end
  
end

mime_types.rb

# config/initializers/mime_types.rb

# Add new mime types for use in respond_to blocks:
# Mime::Type.register "text/richtext", :rtf
Mime::Type.register_alias "text/html", :mobile

sample_controller.rb

class SampleController < ApplicationController
  before_filter :prepare_for_mobile, only: [:index]
  
  def index
    @samples = Sample.all
    
    # if this is an ajax request (X-Requested-With: XMLHttpRequest)
    # note this is true for jQuery mobile page views as well
    if request.xhr? 
      respond_to do |format|
      end
    else
    
    # if you can rely on defaults, you can use
    # respond_to :html, :js
    
    respond_to do |format|
      # if this is a mobile request, it will use index.mobile.erb or fallback on index.html.erb
      format.html
      
      # custom request.format set up in application_controller if its a mobile request
      format.mobile # { render partial: 'index', formats: [:html] }
      
      format.js   # defaults to index.js.erb, used when http accept header is text/javascript, application/javascript, application/x-javascript
      format.json { render json: @samples }
      
      format.any(:atom, :rss) { @samples.Sample.all }
      format.all { render text: "All other mime types will fall through to this..." }
    end
  end