Label does not update using Swift - ios

Question

I'm trying to improve a GitHub project I forked (https://github.com/giacmarangoni/Swift-Radio-Pro/tree/xcode8).
After some fixes and changes everything seems to work good but suddenly I noticed a really strange behavior.
When I open "NowPlayingViewController" for the first time and station starts to stream, everything is working and AVPlayer delegate updates user interface as expected (songLabel, titleLabel and albumArtwork).
After that, without stopping radio streaming, I tried to go back to "StationsViewController" and immediately to reopen "NowPlayingViewController" using "Now playing" button.
At this point delegation is still active, streaming is going on, but when song changes all variables in this view controller are updated but I can't say the same for the user interface. I tried to debug and I noticed that labels are populated but not updated. UI updates in the main thread and setNeedDisplay didn't help.
NowPlayingViewController
AVPlayer setup:
func setUpPlayer(){
radioPlayer = Player.radio
radioPlayer.rate = 1
NotificationCenter.default.addObserver(
self,
selector: #selector(self.playerItemDidReachEnd),
name: NSNotification.Name.AVPlayerItemDidPlayToEndTime,
object: self.radioPlayer.currentItem
)
}
Here you can find func onMetaData(_ metaData: [AVMetadataItem]?)).
//*****************************************************************
// MARK: - AVPlayerItem Delegate (for metadata)
//*****************************************************************
extension NowPlayingViewController: CustomAVPlayerItemDelegate {
func onMetaData(_ metaData: [AVMetadataItem]?) {
if let metaDatas = metaData{
startNowPlayingAnimation()
let firstMeta: AVMetadataItem = metaDatas.first!
let metaData = firstMeta.value as! String
var stringParts = [String]()
if metaData.range(of: " - ") != nil {
stringParts = metaData.components(separatedBy: " - ")
} else {
stringParts = metaData.components(separatedBy: "-")
}
// Set artist & songvariables
let currentSongName = track.title
track.artist = stringParts[0].decodeAllChars()
track.title = stringParts[0].decodeAllChars()
if stringParts.count > 1 {
track.title = stringParts[1].decodeAllChars()
}
if track.artist == "" && track.title == "" {
track.artist = currentStation.stationDesc
track.title = currentStation.stationName
}
DispatchQueue.main.async {
if currentSongName != self.track.title {
if kDebugLog {
print("METADATA artist: \(self.track.artist) | title: \(self.track.title)")
}
// Update Labels
self.artistLabel.text = self.track.artist
self.songLabel.text = self.track.title
self.updateUserActivityState(self.userActivity!)
// songLabel animation
self.songLabel.animation = "zoomIn"
self.songLabel.duration = 1.5
self.songLabel.damping = 1
self.songLabel.animate()
// Update Stations Screen
self.delegate?.songMetaDataDidUpdate(self.track)
// Query API for album art
self.resetAlbumArtwork()
self.queryAlbumArt()
}
}
}
}
}
This method is observed in "CustomAVPlayerItem" according to timedMetaData key path; It's fired every time AVPlayer metadatas change. This class is a subclass of AVPlayerItem:
import MediaPlayer
import Foundation
protocol CustomAVPlayerItemDelegate {
func onMetaData(_ metaData:[AVMetadataItem]?)
}
//*****************************************************************
// Makes sure that observers are removed before deallocation
//*****************************************************************
class CustomAVPlayerItem: AVPlayerItem {
var delegate : CustomAVPlayerItemDelegate?
init(url URL:URL)
{
if kDebugLog {print("CustomAVPlayerItem.init")}
super.init(asset: AVAsset(url: URL) , automaticallyLoadedAssetKeys:[])
addObserver(self, forKeyPath: "timedMetadata", options: NSKeyValueObservingOptions.new, context: nil)
}
deinit{
if kDebugLog {print("CustomAVPlayerItem.deinit")}
removeObserver(self, forKeyPath: "timedMetadata")
}
override func observeValue(forKeyPath keyPath: String?, of object: Any?, change: [NSKeyValueChangeKey : Any]?, context: UnsafeMutableRawPointer?) {
if let avpItem: AVPlayerItem = object as? AVPlayerItem {
if keyPath == "timedMetadata" {
delegate?.onMetaData(avpItem.timedMetadata)
}
}
}
}
The following is my AVPlayer:
import MediaPlayer
//*****************************************************************
// This is a singleton struct using Swift
//*****************************************************************
struct Player {
static var radio = AVPlayer()
}
This is the segue function I use to open to "NowPlayingViewController". StationsViewController
override func prepare(for segue: UIStoryboardSegue, sender: Any?) {
if segue.identifier == "NowPlaying" {
self.title = ""
firstTime = false
let nowPlayingVC = segue.destination as! NowPlayingViewController
nowPlayingVC.delegate = self
if let indexPath = (sender as? IndexPath) {
// User clicked on row, load/reset station
if searchController.isActive {
currentStation = searchedStations[indexPath.row]
} else {
currentStation = stations[indexPath.row]
}
nowPlayingVC.currentStation = currentStation
nowPlayingVC.newStation = true
} else {
// User clicked on a now playing button
if let currentTrack = currentTrack {
// Return to NowPlaying controller without reloading station
nowPlayingVC.track = currentTrack
nowPlayingVC.currentStation = currentStation
nowPlayingVC.newStation = false
} else {
// Issue with track, reload station
nowPlayingVC.currentStation = currentStation
nowPlayingVC.newStation = true
}
}
}
}

Answer 1

Here's what I think you're not understanding and what's actually going on.
Normally, when you "go back" from a pushed view controller, the pushed view controller is popped and destroyed. Your pushed view controller is a NowPlayingViewController. It should be destroyed when you "go back" from it to the StationsViewController. Thus, when you show the NowPlayingViewController again, you would have to create a new, different NowPlayingViewController.
Okay, so far so good, provided you understand all of that. But in your case there is a further complication: you have a leak! Your old NowPlayingViewController is not being destroyed. Thus, when you "go back" to the StationsViewController and show the NowPlayingViewController for a second time, there are now two NowPlayingViewControllers — the new one that you see, and the old one that is leaking.
Okay, so your logging continues to show the old NowPlayingViewController, which is still observing and updating. But your eyes are seeing the new NowPlayingViewController, which is doing nothing. And that explains the phenomena you have described.
If this is right — and, from what you've said, I'm pretty sure it is — then you need to reorganize your architecture either so that you don't get this leak or so that when you show the NowPlayingViewController the second time you show the same NowPlayingViewController rather than creating a different one. (The first approach would be better.)