Hands-On Design Patterns with Swift

Using KVO with Swift

As mentioned before, KVO leverages Objective-C's dynamism, which means it doesn't work on structs.

In order to use KVO with your own Swift objects, you have to make them dynamic and compatible with Objective-C using the @objc annotation:

class MyObject: NSObject {    @objc dynamic     var string: String = ""}

Now, the string member is observable, and you can use the following code:

let object = MyObject()var changed = falselet observer = object.observe(\MyObject.string) { (obj, change) in    // Do Something with the new value    changed = true}object.string = "This will emit an event"assert(changed) // ensure changed was calledobserver.invalidate() // Always invalidate!

With this technique, it is possible to listen to multiple changes from ...