ios - 如何在当前播放结束时自动转到下一首轨道？

Question

我是 swift 的新手，我想实现一段代码来帮助我在当前播放的歌曲结束时播放下一首歌曲。我试图复制我的“@IBAction func nextAction”中的代码(效果很好):

@IBAction func nextAction(sender: AnyObject) {
    self.nextTrack()
}

func nextTrack() {

        if trackId == 0 || trackId < 4 {
            if shuffle.on {
                trackId = Int(arc4random_uniform(UInt32(library.count)))
            }else {
                trackId += 1
            }

            if let coverImage = library[trackId]["coverImage"]{
                coverImageView.image = UIImage(named: "\(coverImage).jpg")
            }

            songTitleLabel.text = library[trackId]["title"]
            artistLabel.text = library[trackId]["artist"]

            audioPlayer.currentTime = 0
            progressView.progress = 0

            let path = NSBundle.mainBundle().pathForResource("\(trackId)", ofType: "mp3")

            if let path = path {
                let mp3URL = NSURL(fileURLWithPath: path)

                do {
                    audioPlayer = try AVAudioPlayer(contentsOfURL: mp3URL)
                    audioPlayer.play()

                    NSTimer.scheduledTimerWithTimeInterval(1.0, target: self, selector: #selector(PlayerViewController.updateProgressView), userInfo: nil, repeats: true)
                    progressView.setProgress(Float(audioPlayer.currentTime/audioPlayer.duration), animated: false)

                } catch let error as NSError {
                    print(error.localizedDescription)
                }
            }
        }

}

并尝试将其放入这样的 if 条件中(在 viewDidLoad 中):

if audioPlayer.currentTime >= audioPlayer.duration {
        self.nextTrack()
    }

我没有任何错误，但在运行时此方法不起作用，歌曲结束而没有播放下一首。

为了使情况更清楚，这是我的 Controller :

import UIKit
import AVFoundation

class PlayerViewController: UIViewController {

    @IBOutlet weak var coverImageView: UIImageView!
    @IBOutlet weak var progressView: UIProgressView!
    @IBOutlet weak var songTitleLabel: UILabel!
    @IBOutlet weak var artistLabel: UILabel!
    @IBOutlet weak var shuffle: UISwitch!

    var trackId: Int = 0
    var library = MusicLibrary().library
    var audioPlayer: AVAudioPlayer!

    override func viewDidLoad() {
        super.viewDidLoad()


        // Do any additional setup after loading the view.
        if let coverImage = library[trackId]["coverImage"]{
            coverImageView.image = UIImage(named: "\(coverImage).jpg")
        }

        songTitleLabel.text = library[trackId]["title"]
        artistLabel.text = library[trackId]["artist"]

        let path = NSBundle.mainBundle().pathForResource("\(trackId)", ofType: "mp3")

        if let path = path {
            let mp3URL = NSURL(fileURLWithPath: path)

            do {
                audioPlayer = try AVAudioPlayer(contentsOfURL: mp3URL)
                audioPlayer.play()

                NSTimer.scheduledTimerWithTimeInterval(1.0, target: self, selector: #selector(PlayerViewController.updateProgressView), userInfo: nil, repeats: true)
                progressView.setProgress(Float(audioPlayer.currentTime/audioPlayer.duration), animated: false)

            } catch let error as NSError {
                print(error.localizedDescription)
            }
        }

    }

    override func viewWillDisappear(animated: Bool) {
        audioPlayer.stop()
    }

    func updateProgressView(){

        if audioPlayer.playing {

            progressView.setProgress(Float(audioPlayer.currentTime/audioPlayer.duration), animated: true)
        }

    }


    @IBAction func playAction(sender: AnyObject) {
        if !audioPlayer.playing {
            audioPlayer.play()
        }

    }

    @IBAction func stopAction(sender: AnyObject) {

        audioPlayer.stop()
        audioPlayer.currentTime = 0
        progressView.progress = 0
    }


    @IBAction func pauseAction(sender: AnyObject) {
        audioPlayer.pause()
    }

    @IBAction func fastForwardAction(sender: AnyObject) {
        var time: NSTimeInterval = audioPlayer.currentTime
        time += 5.0

        if time > audioPlayer.duration {
            stopAction(self)
        }else {
            audioPlayer.currentTime = time
        }

    }

    @IBAction func rewindAction(sender: AnyObject) {
        var time: NSTimeInterval = audioPlayer.currentTime
        time -= 5.0

        if time < 0 {
            stopAction(self)
        }else {
            audioPlayer.currentTime = time
        }
    }

    @IBAction func previousAction(sender: AnyObject) {
        if trackId != 0 || trackId > 0 {
            if shuffle.on {
                trackId = Int(arc4random_uniform(UInt32(library.count)))
            }else {
                trackId -= 1
            }

            if let coverImage = library[trackId]["coverImage"]{
                coverImageView.image = UIImage(named: "\(coverImage).jpg")
            }

            songTitleLabel.text = library[trackId]["title"]
            artistLabel.text = library[trackId]["artist"]

            audioPlayer.currentTime = 0
            progressView.progress = 0

            let path = NSBundle.mainBundle().pathForResource("\(trackId)", ofType: "mp3")

            if let path = path {
                let mp3URL = NSURL(fileURLWithPath: path)

                do {
                    audioPlayer = try AVAudioPlayer(contentsOfURL: mp3URL)
                    audioPlayer.play()

                    NSTimer.scheduledTimerWithTimeInterval(1.0, target: self, selector: #selector(PlayerViewController.updateProgressView), userInfo: nil, repeats: true)
                    progressView.setProgress(Float(audioPlayer.currentTime/audioPlayer.duration), animated: false)

                } catch let error as NSError {
                    print(error.localizedDescription)
                }
            }
        }




    }

    @IBAction func swipeDownAction(sender: AnyObject) {
        self.close()
    }

    @IBAction func closeAction(sender: AnyObject) {
        self.close()
    }

    @IBAction func nextAction(sender: AnyObject) {
        self.nextTrack()
    }

    func close() {
        self.dismissViewControllerAnimated(true, completion: nil)
    }


    func nextTrack() {

        if trackId == 0 || trackId < 4 {
            if shuffle.on {
                trackId = Int(arc4random_uniform(UInt32(library.count)))
            }else {
                trackId += 1
            }

            if let coverImage = library[trackId]["coverImage"]{
                coverImageView.image = UIImage(named: "\(coverImage).jpg")
            }

            songTitleLabel.text = library[trackId]["title"]
            artistLabel.text = library[trackId]["artist"]

            audioPlayer.currentTime = 0
            progressView.progress = 0

            let path = NSBundle.mainBundle().pathForResource("\(trackId)", ofType: "mp3")

            if let path = path {
                let mp3URL = NSURL(fileURLWithPath: path)

                do {
                    audioPlayer = try AVAudioPlayer(contentsOfURL: mp3URL)
                    audioPlayer.play()

                    NSTimer.scheduledTimerWithTimeInterval(1.0, target: self, selector: #selector(PlayerViewController.updateProgressView), userInfo: nil, repeats: true)
                    progressView.setProgress(Float(audioPlayer.currentTime/audioPlayer.duration), animated: false)

                } catch let error as NSError {
                    print(error.localizedDescription)
                }
            }
        }

    }
}

所有代码都是用Xcode 7.3.1编写的

Answer 1

您应该使用 AVAudioPlayer 委托(delegate)方法 audioPlayerDidFinishPlaying(player: AVAudioPlayer, successfully flag: Bool) 当音频播放器播放完声音时调用。

1. 让你的 PlayerViewController 像这样确认 AVAudioPlayerDelegate 协议(protocol):

   class PlayerViewController: UIViewController, AVAudioPlayerDelegate {
   

2. 确保将 self 设置为您创建的 audioPlayer 的委托(delegate)，以便在您的 viewDidLoad、previousAction 和nextTrack 需要添加的方法

   audioPlayer.delegate = self
   

   在这一行之后:

   audioPlayer = try AVAudioPlayer(contentsOfURL: mp3URL)
   

3. 现在您可以使用委托(delegate)方法知道音频何时播放完毕并转到下一首轨道，只需将其添加到您的类中:

   func audioPlayerDidFinishPlaying(player: AVAudioPlayer, successfully flag: Bool) {
       if flag {
           self.nextTrack()
       } else {
           // did not finish successfully
       }
   }