Sinatra Mobile Detection using rack-mobile-detect

app.rb

require 'sinatra'
helpers do
  def get_layout
    @layout_default = ( request.env['X_MOBILE_DEVICE'] ? :layout_mobile : true )
  end

end

before do
  get_layout()
end

get "/" do
  erb :index, :layout => @layout_default
end

config.ru

require '<other stuff>'
require 'rack/mobile-detect'

# ... other config.ru stuff ...
use Rack::MobileDetect
# ... other config.ru stuff ...