MPRemoteCommandCenter错误:曲目同时播放多次

Question

我有TableViewController和AudioPlayerViewController。我在使用MPRemoteCommandCenter时遇到了问题。例如:在TableViewController中，我点击手机，然后进入AudioPlayerViewController，下一步我锁定设备，然后用MPRemoteCommandCenter控制我的音乐--一切正常。但是，如果我进一步解锁设备，返回到TableViewController，再次转到AudioPlayerViewController锁定设备，并按下播放/暂停按钮，我的音乐将同时播放两次。如果我重复这个动作，我的音乐将同时播放三次。等等..。如何修复它？

代码：

import UIKit
import AVFoundation
import MediaPlayer

class ViewController: UIViewController, AVAudioPlayerDelegate, UIAlertViewDelegate {
    
    var audioPlayer: AVAudioPlayer!
    let musicOperation = OperationQueue()
    var timer: Timer?
    
    @IBOutlet weak var playButton: UIButton!
    @IBOutlet var timeElapsed: UILabel!
    @IBOutlet var timeDuration: UILabel!
    @IBOutlet weak var logo: UIImageView!
    @IBOutlet weak var slider: UISlider!
    @IBOutlet weak var volumeView: UIView!
    
    var index = 0
    var buttonIndex = 0
    
    var endOfChapterSleepTimer = false
    
    override func viewDidLoad() {
        super.viewDidLoad()
        
        // Table View Index
        buttonIndex = masterIndex
        
        musicOperation.maxConcurrentOperationCount = 1
        
        try? AVAudioSession.sharedInstance().setCategory(AVAudioSessionCategoryPlayback)
        
        UserDefaults.standard.set(index, forKey: "index")
        
        if index > 0 {

            let fileManager = FileManager.default
            let urls = fileManager.urls(for: .documentDirectory, in: .userDomainMask)
            
            if let documentDirectoryURL: NSURL = urls.first as NSURL? {
                
                let soundURL = documentDirectoryURL.appendingPathComponent("/\(masterIndex)/\(index).mp3")
                
                UserDefaults.standard.set(index, forKey: "\(masterIndex)")
                
                do {
                    
                    audioPlayer = try AVAudioPlayer(contentsOf: soundURL!)
                    audioPlayer.delegate = self
                    audioPlayer.prepareToPlay()
                    play(sender:AnyObject.self as AnyObject)
                    restorePlayerCurrentTime()
                    
                    setupMediaPlayerNotificationView()
                    lockScreen()
                    
                } catch {
                    
                }
            }
            
        } else {
            
            let url = Bundle.main.url(forResource: "\(masterIndex)0", withExtension: "m4a")!
            
            do {
                
                audioPlayer = try AVAudioPlayer(contentsOf: url)
                audioPlayer.delegate = self
                audioPlayer.prepareToPlay()
                play(sender:AnyObject.self as AnyObject)
                
                setupMediaPlayerNotificationView()
                lockScreen()
                
            } catch {
                
            }
        }
        
    }
    
    // MARK: - Audio player controller
    
    @IBAction func play(sender: AnyObject) {
        if !audioPlayer.isPlaying{
            audioPlayer.play()
            slider.maximumValue = Float(audioPlayer.duration)
            timer = Timer(timeInterval: 0.1, target: self, selector: #selector(self.updateTime), userInfo: nil, repeats: true)
            RunLoop.main.add(timer!, forMode: .commonModes)
            restorePlayerCurrentTime()
            playButton.setImage(UIImage(named: "pause.png"), for: UIControlState.normal)
        } else {
            audioPlayer.pause()
            playButton.setImage(UIImage(named: "play.png"), for: UIControlState.normal)
            timer?.invalidate()
        }
    }
    
    @IBAction func fastForward(sender: AnyObject) {
        var time: TimeInterval = audioPlayer.currentTime
        time += 15.0 // Go Forward by 15 Seconds
        if time > audioPlayer.duration {
            audioPlayerDidFinishPlaying(audioPlayer, successfully: true)
        } else {
            audioPlayer.currentTime = time
            updateTime()
        }
    }
    
    @IBAction func fastBackward(sender: AnyObject) {
        var time: TimeInterval = audioPlayer.currentTime
        time -= 15.0 // Go Back by 15 Seconds
        if time < 0 {
            audioPlayer.currentTime = 0
            updateTime()
        } else {
            audioPlayer.currentTime = time
            updateTime()
        }
    }
    
    // MARK: - Audio player time
    
    private func restorePlayerCurrentTime() {
        let currentTimeFromUserDefaults : Double? = UserDefaults.standard.value(forKey: "currentTime\(masterIndex)\(index)") as! Double?
        if let currentTimeFromUserDefaultsValue = currentTimeFromUserDefaults {
            audioPlayer.currentTime = currentTimeFromUserDefaultsValue
            slider.value = Float.init(audioPlayer.currentTime)
        }
    }
    
    @objc func updateTime() {
        let currentTime = Int(audioPlayer.currentTime)
        let minutes = currentTime/60
        let seconds = currentTime - minutes * 60
        
        let durationTime = Int(audioPlayer.duration) - Int(audioPlayer.currentTime)
        let minutes1 = durationTime/60
        let seconds1 = durationTime - minutes1 * 60
        
        timeElapsed.text = NSString(format: "%02d:%02d", minutes,seconds) as String
        timeDuration.text = NSString(format: "-%02d:%02d", minutes1,seconds1) as String
        
        UserDefaults.standard.set(currentTime, forKey: "currentTime\(masterIndex)\(index)")
        UserDefaults.standard.set(durationTime, forKey: "durationTime\(masterIndex)\(index)")
        
        slider.value = Float.init(audioPlayer.currentTime)
    }
    
    func audioPlayerDidFinishPlaying(_ audioPlayer: AVAudioPlayer, successfully flag: Bool) {
        
        playButton.setImage(UIImage(named: "play.png"), for: UIControlState.normal)
        
        let currentTime = 0
        let durationTime = 0.1
        UserDefaults.standard.set(currentTime, forKey: "currentTime\(masterIndex)\(index)")
        UserDefaults.standard.set(durationTime, forKey: "durationTime\(masterIndex)\(index)")
        slider.value = Float.init(audioPlayer.currentTime)
        timer?.invalidate()
        
        let path = NSSearchPathForDirectoriesInDomains(FileManager.SearchPathDirectory.documentDirectory, FileManager.SearchPathDomainMask.userDomainMask, true)
        let documentDirectoryPath:String = path[0]
        let fileManager = FileManager()
        let destinationURLForFile = URL(fileURLWithPath: documentDirectoryPath.appendingFormat("/\(masterIndex)/\(index+1).mp3"))
        
        if fileManager.fileExists(atPath: destinationURLForFile.path){
            
        
        index = index + 1
        viewDidLoad()
            
        } else {
            
        }
    }
    
    // MARK: - Audio player lock screen
    
    func lockScreen() {
        
        var albumArtwork : MPMediaItemArtwork!
        let image:UIImage = UIImage(named: "infoImage")!
        
        albumArtwork = MPMediaItemArtwork.init(boundsSize: image.size, requestHandler: { (size) -> UIImage in
            return image
        })
        
        let infotitle = "title"
        
        MPNowPlayingInfoCenter.default().nowPlayingInfo = [
            MPMediaItemPropertyArtist : "",
            MPMediaItemPropertyTitle : infotitle,
            MPMediaItemPropertyArtwork : albumArtwork,
            MPMediaItemPropertyAlbumTitle : "",
            MPNowPlayingInfoPropertyElapsedPlaybackTime : Int(audioPlayer.currentTime),
            MPMediaItemPropertyPlaybackDuration: Int(audioPlayer.duration)]
        
    }
    
    func setupMediaPlayerNotificationView()  {
        
        let commandCenter = MPRemoteCommandCenter.shared()
        
        commandCenter.playCommand.addTarget { event in
            self.audioPlayer.play()
            self.lockScreen()
            self.playButton.setImage(UIImage(named: "pause.png"), for: UIControlState.normal)
            print("play")
            return .success
        }
        
        commandCenter.pauseCommand.addTarget { event in
            self.audioPlayer.pause()
            self.lockScreen()
            self.playButton.setImage(UIImage(named: "play.png"), for: UIControlState.normal)
            print("pause")
            return .success
        }
        
        commandCenter.skipBackwardCommand.preferredIntervals = [15]
        commandCenter.skipBackwardCommand.addTarget { event in
            self.fastBackward(sender: self)
            self.lockScreen()
            print("fastBackward")
            return .success
        }
        
        commandCenter.skipForwardCommand.preferredIntervals = [15]
        commandCenter.skipForwardCommand.addTarget { event in
            self.fastForward(sender: self)
            self.lockScreen()
            print("fastForward")
            return .success
        }
        
        commandCenter.changePlaybackPositionCommand.addTarget(self, action: #selector(self.changedThumbSlider(_:)))
        
    @objc func changedThumbSlider(_ event: MPChangePlaybackPositionCommandEvent) -> MPRemoteCommandHandlerStatus {
        let time = event.positionTime
        audioPlayer.currentTime = TimeInterval(time)
        self.lockScreen()
        return .success
    }
    
    // MARK: - Audio player slider
    
    @IBAction func slide(_ slider: UISlider) {
        musicOperation.cancelAllOperations()
        let operation = BlockOperation()
        audioPlayer.currentTime = TimeInterval(slider.value)
        self.lockScreen()
        musicOperation.addOperation(operation)
    }
    
    override func viewWillDisappear(_ animated: Bool) {
        super.viewWillDisappear(animated)
        audioPlayer.pause()
        timer?.invalidate()
        musicOperation.cancelAllOperations()
    }

    override func viewWillAppear(_ animated: Bool) {
        super.viewWillAppear(animated)
        UIView.setAnimationsEnabled(true)
        
        // Navigation Bar
        
        self.navigationController?.navigationBar.prefersLargeTitles = true
        self.navigationItem.largeTitleDisplayMode = .always
        self.navigationController?.navigationBar.shadowImage = UIImage()
        self.navigationController?.navigationBar.barTintColor = UIColor(red: 55/255, green: 60/255, blue: 65/255, alpha: 1.0)
        self.navigationController?.navigationBar.isTranslucent = true
        self.navigationController?.navigationBar.tintColor = .white
        self.navigationItem.backBarButtonItem = UIBarButtonItem(title: "", style: .plain, target: nil, action: nil)
    }
    
    override func didReceiveMemoryWarning() {
        super.didReceiveMemoryWarning()
    }
    
}

Answer 1

发生的情况是，每次您转到AudioPlayerViewController时都会启用MPRemoteCommandCenter，但是当您返回到TableViewController时，您不会调用removeTarget。这是你的问题。

在viewWillDisappear to removeTarget中调用类似下面的内容

func setupMediaPlayerNotificationView(_ enable: Bool)  {

let commandCenter = MPRemoteCommandCenter.shared()

if enable {
    commandCenter.playCommand.addTarget(self, action: #selector(self.lockScreenPlay(_:)))
    commandCenter.pauseCommand.addTarget(self, action: #selector(self.lockScreenPlay(_:)))
    commandCenter.nextTrackCommand.addTarget(self, action: #selector(self.lockScreenNextTrack(_:)))
    commandCenter.previousTrackCommand.addTarget(self, action: #selector(self.lockScreenPreviousTrack(_:)))
} else {
    commandCenter.playCommand.removeTarget(self, action: #selector(self.lockScreenPlay(_:)))
    commandCenter.pauseCommand.removeTarget(self, action: #selector(self.lockScreenPlay(_:)))
    commandCenter.nextTrackCommand.removeTarget(self, action: #selector(self.lockScreenNextTrack(_:)))
    commandCenter.previousTrackCommand.removeTarget(self, action: #selector(self.lockScreenPreviousTrack(_:)))
    }
}

后续问题示例：

@objc func lockScreenPlay(_ event: MPRemoteCommandEvent) -> MPRemoteCommandHandlerStatus {
    self.playButton(AnyObject.self)
    return .success
}

@objc func lockScreenNextTrack(_ event: MPRemoteCommandEvent) -> MPRemoteCommandHandlerStatus {
        self.playerDidFinishPlaying()
    return .success
}