swift ask music permission for initial view controller - ios

Question

I have a split view controller with the top view controller set to a table view controller that is to display a list of playlists for selection. The first time the app is loaded it asks for music access permission. Answering yes does give it permission but the table view displays no playlists. I end up having to kill the app and run it again. Am I asking for music library permission the wrong place? It is in that top view controller's viewWillAppear and store the playlists I'm using (since some are screened out) in a class of playlists.
override func viewWillAppear(_ animated: Bool) {
self.clearsSelectionOnViewWillAppear = self.splitViewController!.isCollapsed
super.viewWillAppear(animated)
checkMediaAccessAndSetup()
}
func checkMediaAccessAndSetup() {
let authorizationStatus = MPMediaLibrary.authorizationStatus()
switch authorizationStatus {
case .notDetermined:
// Show the permission prompt.
MPMediaLibrary.requestAuthorization({[weak self] (newAuthorizationStatus: MPMediaLibraryAuthorizationStatus) in
// Try again after the prompt is dismissed.
self?.checkMediaAccessAndSetup()
})
case .denied, .restricted:
// Do not use MPMediaQuery.
return
default:
// Proceed as usual.
break
}
// Do stuff with MPMediaQuery
self.setupPlaylistStore()
tableView.reloadData()
}

Answer 1

The chief problems with your code are
You are completely failing to grapple with the fact that the requestAuthorization completion function is called on a background thread. You need to step out to the main thread to do work on the interface.
You have omitted the all-important .authorized case. When you have work to do that depends upon your authorization status, you must do it now if you are authorized, but after authorization if you are not determined.
Thus, this is the correct scheme for a coherent authorization check (where f() is the thing you always want to do if you can):
let status = MPMediaLibrary.authorizationStatus()
switch status {
case .authorized:
f()
case .notDetermined:
MPMediaLibrary.requestAuthorization() { status in
if status == .authorized {
DispatchQueue.main.async {
f()
}
}
}
// ...
}
If you abstract this code into a utility method, where f can be anything, you can do this everywhere in your app where authorization might be necessary — not merely at startup.

Answer 2

Thanks for the comments, it gave me clues of the multi-threading that was going on and I was able to fix it with a timer call if there were no playlists in the class to keep on checking and reload the table data.
override func viewWillAppear(_ animated: Bool) {
self.clearsSelectionOnViewWillAppear = self.splitViewController!.isCollapsed
super.viewWillAppear(animated)
checkMediaAccess()
self.setupPlaylistStore()
tableView.reloadData()
if store.allPlaylists.count < 1 {
playlistTimer = Timer.scheduledTimer(timeInterval: 1.0, target: self, selector: #selector(self.playlistTimerCall), userInfo: nil, repeats: true)
}
}
#objc func playlistTimerCall() {
self.setupPlaylistStore()
if store.allPlaylists.count > 1 {
tableView.reloadData()
playlistTimer?.invalidate()
}
}
func checkMediaAccess() {
let authorizationStatus = MPMediaLibrary.authorizationStatus()
switch authorizationStatus {
case .notDetermined:
// Show the permission prompt.
MPMediaLibrary.requestAuthorization({[weak self] (newAuthorizationStatus: MPMediaLibraryAuthorizationStatus) in
// Try again after the prompt is dismissed.
self?.checkMediaAccess()
})
case .denied, .restricted:
// Do not use MPMediaQuery.
return
default:
// Proceed as usual.
break
}
}
func setupPlaylistStore() {
// purge store
store.clearAllPlaylists()
// create a query of media items in playlist
let myPlayListsQuery = MPMediaQuery.playlists()
if myPlayListsQuery.collections != nil {
playlists = myPlayListsQuery.collections!
}
// add playlists to MyPlaylist(s)
if playlists.count > 0 {
for index in 0...playlists.count - 1 {
let playlist = playlists[index]
store.addPlaylist(playlist: playlist as! MPMediaPlaylist)
}
}
var toBeRemoved = [Int]()
let defaults = UserDefaults.standard
if defaults.bool(forKey: "exclude_smart_playlists") {
//smart
for index in 0...(playlists.count - 1) {
let playlist = playlists[index]
let theAttributes = playlist.value(forProperty: MPMediaPlaylistPropertyPlaylistAttributes) as! Int
if theAttributes == 2 {
toBeRemoved.append(index)
}
}
}
if defaults.bool(forKey: "exclude_folders") {
//folders
for index in 0...(playlists.count - 1) {
let playlist = playlists[index]
let isFolder = playlist.value(forProperty: "isFolder")
let stringIsFolder = String("\(String(describing: isFolder))")
if ((stringIsFolder.range(of: "1")) != nil) {
toBeRemoved.append(index)
}
}
}
//sort from the last to the first so i don't reindex
let reverseSortedPlaylists = toBeRemoved.sorted(by: >)
// remove the unwanted playlists
for list in reverseSortedPlaylists {
store.removePlaylist(index: list)
}
}