How to get Notification from standalone class (Swift 3) - ios

Question

I want to call method in a class as soon as observer get Notification in another one. The problem is that I cannot call one class from another, because I will get recursion call then.
1) Controller class with Player instance:
// PlayerController.swift
// player
import UIKit
import MediaPlayer
class NowPlayingController: NSObject {
var musicPlayer: MPMusicPlayerController {
if musicPlayer_Lazy == nil {
musicPlayer_Lazy = MPMusicPlayerController.systemMusicPlayer()
let center = NotificationCenter.default
center.addObserver(
self,
selector: #selector(self.playingItemDidChange),
name: NSNotification.Name.MPMusicPlayerControllerNowPlayingItemDidChange,
object: musicPlayer_Lazy)
musicPlayer_Lazy!.beginGeneratingPlaybackNotifications()
}
return musicPlayer_Lazy!
}
//If song changes
func playingItemDidChange(notification: NSNotification) {
//somehow call updateSongInfo() method from 2nd class
}
//Get song metadata
func getSongData() -> (UIImage, String?, String?) {
let nowPlaying = musicPlayer.nowPlayingItem
//...some code
return (albumImage, songName, artistAlbum)
}
func updateProgressBar() -> (Int?, Float?){
let nowPlaying = musicPlayer.nowPlayingItem
var songDuration: Int?
var elapsedTime: Float?
songDuration = nowPlaying?.value(forProperty: MPMediaItemPropertyPlaybackDuration) as? Int
elapsedTime = Float(musicPlayer.currentPlaybackTime)
return(songDuration, elapsedTime)
}
}
2) View controller which should be updated when Player Controller get notification
// MainViewController.swift
// player
import UIKit
class MainViewController: UIViewController {
let playerController = PlayerController()
#IBOutlet weak var albumView: UIImageView!
#IBOutlet weak var songLabel: UILabel!
#IBOutlet weak var artistAlbum: UILabel!
override func viewDidLoad() {
super.viewDidLoad()
//Start updating progress bar
Timer.scheduledTimer(timeInterval: 0.5,
target: self,
selector: #selector(MainViewController.updateProgressBar),
userInfo: nil,
repeats: true)
}
private func updateSongInfo(){
(albumView.image!, songLabel.text, artistAlbum.text) = playerController.getSongData()
}
private func updateProgressBar(){
(progressBar.maximumValue, progressBar.value) = playerController.playingItemProgress()
}
}
Solution for Swift 3:
In NowPlayingController:
let newSongNotifications = NSNotification(name:NSNotification.Name(rawValue: "updateSongNotification"), object: nil, userInfo: nil)
func playingItemDidChange(notification: NSNotification) {
NotificationCenter.default.post(newSongNotifications as Notification)
}
And in other controller:
override func viewDidLoad() {
super.viewDidLoad()
NotificationCenter.default.addObserver(self, selector: #selector(self.updateSongInfo), name: NSNotification.Name(rawValue: "updateSongNotification"), object: nil)
}

Answer 1

You can post a notification from within your custom object where you need it:
let notification = NSNotification(name:"doSomethingNotification", object: nil, userInfo: nil)
NotificationCenter.defaultCenter.postNotification(notification)
And then in your other view controller in which you want to execute something in response to this notification, you tell it to observe the notification in viewDidLoad(). The selector you pass in is the method you want to be executed when the notification is received.
override func viewDidLoad(){
super.viewDidLoad()
NotificationCenter.addObserver(self, selector: #selector(self.doSomething), name: "doSomethingNotification", object: nil)
}

Answer 2

You can use delegate method to update MainViewController