title: iOS: what is the equivalent of an event listener in Objective-C?
body: <p>In some of my learning I saw someone mention that in your view controller you can have a model and have some sort of listener on the model for changes in it.  I don't think I'm using the right names for these, which is probably why my searches haven't turned up anything.  Essentially I want to move my server calls from the controllers into my models, but I need some sort of listener on them to know when the call is complete to update my views.</p>