Creating an observer to check if MediaPlayer playbackState is paused or not - swift

Question

I have a music app and I wish to determine if playback has been paused while the app was closed (due to an event like a phone call or AirPods being taken out of ear etc)
My first approach was to run a func inside of viewWillAppear that checked
if mediaPlayer.playbackState == .paused {
...
}
If it was paused I updated the play/pause button image. However, this did not work, the play/pause button would still show Play even if it was paused.
Next, I tried adding an observer to the viewDidLoad
NotificationCenter.default.addObserver(self, selector: #selector(self.wasSongInterupted(_:)), name: UIApplication.didBecomeActiveNotification, object: self.mediaPlayer)
The self.wasSongInterupted I call is
#objc func wasSongInterupted(_ notification: Notification) {
DispatchQueue.main.async {
if self.mediaPlayer.playbackState == .paused {
print("paused")
self.isPlaying = false
self.playPauseSongButton.isSelected = self.isPlaying
} else if self.mediaPlayer.playbackState == .playing {
self.isPlaying = true
self.playPauseSongButton.isSelected = self.isPlaying
}
}
}
However, I am still having the same issue.
What is the best way to determine if my music player is playing or paused when I reopen the app?
Edit 1: I Edited my code based on comments.
wasSongInterrupted was not being called, and through breakpoints and errors I discovered the code was mostly not needed. I changed my code to be
func wasSongInterrupted() {
DispatchQueue.main.async {
if self.mediaPlayer.playbackState == .interrupted {
var isPlaying: Bool { return self.mediaPlayer.playbackState == .playing }
print("Playback state is \(self.mediaPlayer.playbackState.rawValue), self.isPlaying Bool is \(self.isPlaying)")
self.playPauseSongButton.setImage(UIImage(named: "playIconLight"), for: .normal)
//self.playPauseSongButton.isSelected = self.isPlaying
}
}
}
and inside my AppDelegate's applicationDidBecomeActive I have
let mediaPlayerVC = MediaPlayerViewController()
mediaPlayerVC.wasSongInterupted()
Now the code runs, however I have an issue.
If I run the following code:
if self.mediaPlayer.playbackState == .interrupted {
print("interrupted \(self.isPlaying)")
}
and then make a call and come back to the app it will hit the breakpoint. It will print out interrupted as well as false which is the Bool value for self.isPlaying
However if I try to update the UI by
self.playPauseSongButton.isSelected = self.isPlaying
or by
self.playPauseSongButton.setImage(UIImage(named: "playIconLight.png"), for: .normal)
I get an error message Thread 1: EXC_BREAKPOINT (code=1, subcode=0x104af9258)

Answer 1

You trying to update you player UI from viewWillAppear. From Apple Documentation:
viewWillAppear(_:)
This method is called before the view controller's view is about to be added to a view hierarchy and before any animations are configured for showing the view.
So if your app was suspended and the becomes active again, this method won't be called, because your UIViewController is already at Navigations Stack.
If you want to catch the moment when your app becomes active from suspended state, you need to use AppDelegate. From Apple Documentation:
applicationDidBecomeActive(_:)
This method is called to let your app know that it moved from the inactive to active state. This can occur because your app was launched by the user or the system.
So you need to use this method at your AppDelegate to handle app running and update your interface.
UPDATE
You saying the inside this AppDelegate method you're doing
let mediaPlayerVC = MediaPlayerViewController()
mediaPlayerVC.wasSongInterupted()
That's wrong because you're creating a new view controller. What you need to do, is to access you existing view controller from navigation stack and update it.
One of the possible solutions is to use NotificationCenter to send a notification. You view controller should be subscribed to this event of course.
At first, you need to create a notification name
extension Notification.Name {
static let appBecameActive = Notification.Name(rawValue: "appBecameActive")
}
Then in you AppDelegate add following code to post your notifications when app becomes active
func applicationDidBecomeActive(_ application: UIApplication) {
NotificationCenter.default.post(name: .appBecameActive, object: nil)
}
And finally in your view controller add to subscribe it on notifications
override func viewDidLoad() {
super.viewDidLoad()
NotificationCenter.default.addObserver(self,
selector: #selector(wakeUp),
name: .appBecameActive,
object: nil)
...
}
#objc func wakeUp() {
// Update your UI from here
}
Hope it helps you.