Notifications

Using NotificationCenter you can communicate from one class to another. For example, while executing code in one class you can notify the UI to update something.

Basic Setup

In a separate class you might "post" a notification. In this example I named the post "updateView". Notifications is a 3 step process:

Step 1 - Setup Post Names

 
extension Notification.Name {
    static let updateView = NSNotification.Name("updateView")
}
 

Step 2 - Post Notification

To pass data, you can send a dictionary to the userInfo parameter.

 
var userInfo: [String: String] = ["extraData": "Some extra data"]
userInfo["moreData"] = "Some more data"
NotificationCenter.default.post(name: .updateView, object: self, 
    userInfo: userInfo)
 

Step 3 - Observe Notification

Then in your ViewController you might be "observing" for that particular post called "updateView" in the notification center:

 
override func viewDidLoad() {
    super.viewDidLoad()
    NotificationCenter.default.addObserver
            (forName: .updateView, object: nil, 
             queue: OperationQueue.main) {
        (notification) in
        // Get values from the class that sent the notification
        let poster = notification.object as! ClassThatPostedNotification
        let propertyValue = poster.property

        // Get values from userInfo
        let extraData = notification.userInfo?["extraData"] as! String
        let moreData = notification.userInfo?["moreData"] as! String
    }
}
 

So the ViewController will be observing any post called "updateView" and when it observes a post it calls updateView. I usually name my posts and functions the same name because...well, I am a simple guy. :)

(Swift 4)