NSNotification in Swift

While Apple has put a lot of design patterns to develop applications for iOS, the flexibility of an event driven application development surely has its merits. The very de-coupled application is so nice to play around with. Well, the downside is to find where is what. For a strictly coupled application, one can definitely find the root of the roots. But for a de-coupled application its very difficult to find what is happening where. Then comes good practices of code commeting and logger messages to rescue. That topic is a separate post I hope.

Lets see how in swift we could write an event driven application.

Here is a scenario. We have a ViewController1.swift and MyViewController.swift. First ViewController1 is loaded in the application and then it navigates to MyViewController. Upon certain situation in MyViewController we want to do something on ViewController1. All we have to do is send an event from MyViewController to ViewController1. The events here in iOS is known as NSNotification. So the setup is as shown here.

// MyViewController.swift
// Dispatch Event from wherever necessary
let notification = NSNotification(name: "myNotification" , object: self, userInfo:nil )
NSNotificationCenter.defaultCenter().postNotification(notification)

Then in the other file just add the listeners to listen to the events and call the methods to handle them.

// ViewController1.swift
override func viewDidLoad() {
    super.viewDidLoad()
    // Listen for Event
    NSNotificationCenter.defaultCenter().addObserver( self, selector: #selector(onGotNotification),name: "myNotification", object: nil )
}
private func onGotNotification(notification:NSNotification){
    print("name=",notification.name)
    print("object=",notification.object)
    //
    let myViewController:MyViewController = notification.object as! MyViewController
    myViewController.someMethod()
}

Happy coding.