Using AVAudioPlayer with Dynamic URL in Swift 3 causing Thread Errors - ios

Question

I am new to Swift and making an audio app using AVAudioPlayer. I am using a remote URL mp3 file for the audio, and this works when it's static.
For my use case, I want to pull a URL for an mp3 file from a JSON array and then pass it into the AVAudioPlayer to run.
If I move the AVAudioPlayer block into the ViewDidLoad and make the mp3 file a static URL, it will run fine.
Then, when I move this code into my block that extracts an mp3 url from JSON, I can print the URL successfully. But when I pass it into my audio player, problems arise. Here's the code.
override func viewDidLoad() {
super.viewDidLoad()
let url = URL(string: "http://www.example.com/example.json")
URLSession.shared.dataTask(with:url!, completionHandler: {(data, response, error) in
guard let data = data, error == nil else { return }
let json: Any?
do{
json = try JSONSerialization.jsonObject(with: data, options: [])
}
catch{
return
}
guard let data_list = json as? [[String:Any]] else {
return
}
if let foo = data_list.first(where: {$0["episode"] as? String == "Example Preview"}) {
self.audiotest = (foo["audio"] as? String)!
print(self.audiotest) // this prints
// where i'm passing it into the audio player
if let audioUrl = URL(string: self.audiotest) {
// then lets create your document folder url
let documentsDirectoryURL = FileManager.default.urls(for: .documentDirectory, in: .userDomainMask).first!
// lets create your destination file url
let destinationUrl = documentsDirectoryURL.appendingPathComponent(audioUrl.lastPathComponent)
//let url = Bundle.main.url(forResource: destinationUrl, withExtension: "mp3")!
do {
audioPlayer = try AVAudioPlayer(contentsOf: destinationUrl)
} catch let error {
print(error.localizedDescription)
}
} // end player
// ....
Specifically, I get an error Thread 1: Fatal error: Unexpectedly found nil while unwrapping an Optional value when clicking a play button IBAction that is connected to the audio player. Finally, that action function looks like this:
#IBAction func playPod(_ sender: Any) {
audioPlayer.play()
}
Do you know where I'm going wrong? I'm confused as to why I can't print the URL and also get a response that the URL is nil in the same block, but maybe that's an asynchronous thing.

Answer 1

The problem is that you didn't save the mp3 file to documents and trying to play it
this line
audioPlayer = try AVAudioPlayer(contentsOf: destinationUrl)
assumes that there is a saved mp3 file in that path , but acutally there is no files you appended the audio extension on the fly
besides for steaming audio from a remote server, use AVPlayer instead of AVAudioPLayer.
AVPlayer Documentation
Also try this with urls parsed from json
var urlStr = (foo["audio"] as? String)!
self.audiotest = urlStr.addingPercentEncoding(withAllowedCharacters: .urlHostAllowed)