At the above link, I see the following in regards to how the model layer should communicate with the ViewController.
"When a model object changes (for example, new data is received over a network connection), it notifies a controller object, which updates the appropriate view objects."
My question is, how does the model object notify the Controller object? What are various ways this can be done? My model layer gets the user's location and then calls a web service. How should I notify the controller object when that data is downloaded?