Using AVAudioPlayer with Dynamic URL in Swift 3 causing Thread Errors

问题

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.

回答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)

来源：https://stackoverflow.com/questions/48431455/using-avaudioplayer-with-dynamic-url-in-swift-3-causing-thread-errors

标签

ios

swift

avaudioplayer