Rails preferred_layout

application_controller.rb

class ApplicationController < ActionController::Base
  layout :conditionally_select_layout

  # Like  `layout`, but allows conditional overriding in app controller
  def self.preferred_layout(value = nil)
    @preferred_layout = value unless value.nil?
    @preferred_layout
  end

  private

  def conditionally_select_layout
    if request.xhr? && request.params[:layout] == "false"
      false
    elsif devise_controller?
      "modal"
    else
      self.class.preferred_layout
    end
  end
end