title: Swift: Delegates / Events coming from C# background
body: <p>I have a Business Logic class that returns an object after making a simple web service call. It is called when a button is tapped (in my view controller). This call to my Business Logic class may take a few seconds to run and I don't want to block the main thread. </p>
  
  <p>How do I raise an event in my Business Logic class that my ViewController can subscribe to, so that I know it's time to process and display the object?</p>