我无法在后台播放音乐 (Xcode 9, Swift 4)

Question

如问题所示，我需要我的应用程序像大多数音乐播放器一样在后台播放音乐。我试图在网上找到一些东西，但它们不起作用。有人可以看看我的问题吗？我认为苹果可能会在后台自动终止我的应用程序，因为它可以在后台播放几秒钟（可能是 10 秒）。

此外，我想把音乐放在另一个viewController中播放。现在，每当我回到根 viewController 时，音乐总是会停止。

这是我的代码。

//
//  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()
        }
    }
}

Answer 1

打开项目，继续功能并启用背景模式和select音频、AirPlay和画中画。它将在您的 Info.plist 文件中为后台音频添加一个键。

Answer 2

在这个问题上花了几天时间，我终于弄明白了。在swift 4中，我认为我们需要在项目目录下的appDelegate class中添加几行代码。像这样：

import UIKit
import AVFoundation

@UIApplicationMain
class AppDelegate: UIResponder, UIApplicationDelegate {

    var window: UIWindow?

    func application(_ application: UIApplication, didFinishLaunchingWithOptions launchOptions: [UIApplicationLaunchOptionsKey: Any]?) -> Bool {
        // Override point for customization after application launch.
        let session = AVAudioSession.sharedInstance()
        do{
            try session.setActive(true)
            try session.setCategory(AVAudioSessionCategoryPlayback)
        } catch{
            print(error.localizedDescription)
        }
        return true
    }

    func applicationWillResignActive(_ application: UIApplication) {
        // Sent when the application is about to move from active to inactive state. This can occur for certain types of temporary interruptions (such as an incoming phone call or SMS message) or when the user quits the application and it begins the transition to the background state.
        // Use this method to pause ongoing tasks, disable timers, and invalidate graphics rendering callbacks. Games should use this method to pause the game.
    }

    func applicationDidEnterBackground(_ application: UIApplication) {
        // Use this method to release shared resources, save user data, invalidate timers, and store enough application state information to restore your application to its current state in case it is terminated later.
        // If your application supports background execution, this method is called instead of applicationWillTerminate: when the user quits.
    }

    func applicationWillEnterForeground(_ application: UIApplication) {
        // Called as part of the transition from the background to the active state; here you can undo many of the changes made on entering the background.
    }

    func applicationDidBecomeActive(_ application: UIApplication) {
        // Restart any tasks that were paused (or not yet started) while the application was inactive. If the application was previously in the background, optionally refresh the user interface.
    }

    func applicationWillTerminate(_ application: UIApplication) {
        // Called when the application is about to terminate. Save data if appropriate. See also applicationDidEnterBackground:.
    }
}

更新：Swift4.2

这对我也有帮助：

1.第一步：

2. 第二个：

func application(_ application: UIApplication, didFinishLaunchingWithOptions launchOptions: [UIApplication.LaunchOptionsKey: Any]?) -> Bool {
    // Override point for customization after application launch.

    let session = AVAudioSession.sharedInstance()
    do{
        try session.setActive(true)
        try session.setCategory(.playback, mode: .default,  options: .defaultToSpeaker)
    } catch{
        print(error.localizedDescription)
    }
    return true
}

Answer 3

对我来说，我的应用程序在我的应用程序中有权利“NSFileProtectionComplete”。这导致音频在应用进入后台后不久停止播放。

使用此设置，如果您的应用导入音频文件（而不是与应用捆绑），那么您需要编写文件使其具有在后台播放的权限，否则默认情况下文件将全部具有“completeFileProtection”和AVAudioPlayer在进入后台后不久将无法解码您的文件。

try data.write(to: fileURL, options: .completeFileProtectionUnlessOpen)

来自： https://developer.apple.com/documentation/uikit/protecting_the_user_s_privacy/encrypting_your_app_s_files

我无法在后台播放音乐 (Xcode 9, Swift 4)

I cannot play music in the background (Xcode 9, Swift 4)

ios

swift

avfoundation

swift4

avaudioplayer