another_controller.rb

class AnotherController < UIViewController

  def loadView 
  end

  def viewDidLoad
    super
    @label = UILabel.new
    @label.text = 'Some Foo text'
    @label.frame = [[50,50],[150,50]]
    self.view.addSubview(@label) #app runs fine if this is deleted
  end

end

app_delegate.rb

class AppDelegate
  def application(application, didFinishLaunchingWithOptions:launchOptions)
    @window = UIWindow.alloc.initWithFrame(UIScreen.mainScreen.bounds)
    @window.makeKeyAndVisible

    nav = UINavigationController.alloc.initWithRootViewController(HomeController.alloc.initWithNibName(nil, bundle:nil))
    nav.wantsFullScreenLayout = true
    @window.rootViewController = nav
    true
  end
end

home_controller.rb

class HomeController < UIViewController

  def viewWillAppear(animated)
    super
    self.navigationController.navigationBarHidden = true
  end
  def viewWillDisappear(animated)
    super
    self.navigationController.navigationBarHidden = false
  end

  def viewDidLoad
    super

    button = UIButton.buttonWithType(UIButtonTypeRoundedRect)
    button.frame = [[15,100], [280,50]]
    button.setTitle("Move to next view", forState: UIControlStateNormal)
    button.addTarget(self, 
                     action: "moveToChildView:",
                     forControlEvents: UIControlEventTouchUpInside)

    self.view.addSubview button
  end

  def moveToChildView (sender)
    self.parentViewController.pushViewController(AnotherController.alloc.initWithNibName(nil, bundle: nil), animated:true)
  end
end