Getting property changing notifications using property observers

You may often find that you would like to know when a property changes its value; maybe you want to update the value of another property, or inform a delegate. In Objective-C, this was often accomplished by writing your own getter and setter, or using Key-Value observing (KVO), but we have native support for property observers in Swift.

Getting ready

To examine property observers, we should create an object with a property that we want to observe. Let's create an object to manage users and a property to hold the current user's name:

class UserManager { 
    var currentUserName: String = "Emmanuel Goldstein" 
} 

We want to present some friendly...