app_delegate.rb

class AppDelegate
  include BW::KVO

  attr_accessor :user

  def application(application, didFinishLaunchingWithOptions:launchOptions)

    @window = UIWindow.alloc.initWithFrame(UIScreen.mainScreen.applicationFrame)
    @window.makeKeyAndVisible

    @name_label = UILabel.alloc.initWithFrame(CGRectMake(0, 0, 100, 30))
    @window.addSubview(@name_label)

    @email_label = UILabel.alloc.initWithFrame([[0, @name_label.frame.size.height + 10], @name_label.frame.size])
    @window.addSubview(@email_label)

    @id_label = UILabel.alloc.initWithFrame([[0, @email_label.frame.origin.y + @email_label.frame.size.height + 10], @name_label.frame.size])
    @window.addSubview(@id_label)

    self.user = User.new

    ["name", "id", "email"].each do |prop|
      observe(self.user, prop) do |old_value, new_value|
        instance_variable_get("@#{prop}_label").text = new_value
      end
    end

    true
  end
end