问我不能在后台播放音乐(Xcode 9，Swift 4)

EN

//
//  MusicLibraryTableViewController.swift
//  WF
//
//  Created by Bo Ni on 7/1/18.
//  Copyright © 2018 Bo Ni. All rights reserved.
//

import UIKit
import AVFoundation

class MusicLibraryTableViewController: UITableViewController, AVAudioPlayerDelegate{

    let songs: [String] = ["After Master"]

    let producer: [String] = ["August Wu/Zoro"]

    let identifier = "musicIdentifier"

    var audioPlayer: AVAudioPlayer?

    var isAudioPlayerPlaying = false

    // MARK: - Table view data source

    override func numberOfSections(in tableView: UITableView) -> Int {
        // #warning Incomplete implementation, return the number of sections
        return 1
    }

    override func tableView(_ tableView: UITableView, cellForRowAt
        indexPath: IndexPath) -> UITableViewCell {

        let cell: MusicTableViewCell = self.tableView.dequeueReusableCell(withIdentifier: identifier) as! MusicTableViewCell
        cell.producerLabel.text = producer[indexPath.row]
        cell.musicNameLabel.text = songs[indexPath.row]
        cell.playButton.setImage(UIImage(named:"Play Button")?.withRenderingMode(.alwaysOriginal), for: UIControlState.normal)

        return cell
    }

    override func tableView(_ tableView: UITableView, heightForRowAt indexPath: IndexPath) -> CGFloat {
        return 64.0
    }

    override func tableView(_ tableView: UITableView, numberOfRowsInSection section: Int) -> Int {
        // #warning Incomplete implementation, return the number of rows
        return songs.count
    }

    override func tableView(_ tableView: UITableView,
        didSelectRowAt indexPath: IndexPath) {

        let cell: MusicTableViewCell = self.tableView.cellForRow(at: indexPath) as! MusicTableViewCell

        let music = NSURL.fileURL(withPath: Bundle.main.path(forResource: songs[indexPath.row], ofType: "mp3")!)
        do {
            try audioPlayer = AVAudioPlayer(contentsOf: music)
        } catch{
            print(error.localizedDescription)
        }

        UIApplication.shared.beginReceivingRemoteControlEvents()

        audioPlayer?.delegate = self
        audioPlayer?.prepareToPlay()

        if isAudioPlayerPlaying == true{
            stopAudio()
            isAudioPlayerPlaying = false
            cell.playButton.setImage(UIImage(named: "Play Button"), for: UIControlState.normal)
        }else{
            prepareAudio()
            playAudio()
            isAudioPlayerPlaying = true
            cell.playButton.setImage(UIImage(named: "Stop Button"), for: UIControlState.normal)
        }
    }

    func prepareAudio(){
        do {
            //keep alive audio at background
            try AVAudioSession.sharedInstance().setCategory(AVAudioSessionCategoryPlayback)
        } catch _ {
        }
        do {
            try AVAudioSession.sharedInstance().setActive(true)
        } catch _ {
        }
    }

    func playAudio(){
        if let player = audioPlayer{
            player.play()
        }
    }

    func stopAudio(){
        if let player = audioPlayer{
            player.stop()
        }
    }
}