rm_delegate.rb

# Example of delegation in RubyMotion
class MsActivityView < UIView
  attr_accessor :delegate
  def initWithFrame(frame)
    super
    #...
    @cancelButton = UIButton.alloc.init
    @cancelButton.addTarget(
      self,
      action: :cancel,
      forControlEvents:UIControlEventTouchUpInside
    )
  end
  def cancel   
    self.delegate.public_send(:activityViewDidCancel, self)
  end
end

class MsScannerViewController < UIViewController
  # ...
  def setActivityView(show)
    activityIndicator = MsActivityView.alloc.initWithFrame(frame)
    activityIndicator.text = "Searching"
    activityIndicator.isAnimating = true
      
    # Define delegation
    activityIndicator.delegate = self
      
    # Place activity view at the navigation controller level to make sure it ignores tap gestures
    self.navigationController.view.addSubview(activityIndicator)
   
  end
  def activityViewDidCancel(view)
    self.scannerSession.cancel
  end
end