我有一个UITableViewController，其中有一组自定义单元格，其中有一个playButton。在cellForRowAtIndexPath中，我分配了一个等于按钮的indexPath的标记，这样当按下playButton时，我将按钮的标题设置为“Stop”。它会更改为“Stop”，这是应该的，当我按下“Stop”时，它会更改回“Play”。
我遇到的困难是当我的声音在没有用户干预的情况下自动停止播放时。我设置了一个观察器来监听MP3播放器正在播放的声音。我在MyTableViewController的viewDidLoad中添加了一个观察器：
下面是我用来更改单元格中playButton的标题的变量：

// Variables to facilitate changing playButton title
var indexPathOfPlayButton = Int()
var isPlaying: Bool = false

在MyTableViewController的viewDidLoad中，我添加了这个观察者：

NSNotificationCenter.defaultCenter().addObserver(self, selector: "resetPlayButton", name: resetPlayButtonNotification, object: nil)

下面是MyTableViewController上的playMP3方法：

func playMP3(sender: AnyObject) {

    if isPlaying == false {
        isPlaying = true
        // This gets the indexPath of the button that sent the playMP3 request
        let indexPath = sender.tag
        sender.setTitle("Stop", forState: UIControlState.Normal)

        // This sets the indexPath of the playButton that we'll redraw the button when it receives a notification?
        indexPathOfPlayButton = indexPath

        if resultsSearchController.active {
            let soundToPlay = self.filteredSounds[indexPath]
            let soundFilename = soundToPlay.soundFilename as String
            mp3Player = MP3Player(fileName: soundFilename)
            mp3Player.play()
        } else {
            let soundToPlay = self.unfilteredSounds[indexPath]
            let soundFilename = soundToPlay.soundFilename as String
            mp3Player = MP3Player(fileName: soundFilename)
            mp3Player.play()
        }
    }

    else if isPlaying == true {
        isPlaying = false
        sender.setTitle("Play", forState: UIControlState.Normal)
        mp3Player.stop()
    }
}

在我的MP3Player类中，这是我用来发布完成通知的委托方法：

func audioPlayerDidFinishPlaying(player: AVAudioPlayer, successfully flag: Bool) {
    if currentTrackIndex == tracks.count - 1 {
        print("end of playlist reached")
        player.stop()
        NSNotificationCenter.defaultCenter().postNotificationName(resetPlayButtonNotification, object: self)
    }

    else if flag == true {
        print("advance to next track")
        nextSong(true)
    }
}

最后，这是MyTableViewController上的方法，在发布通知时调用该方法：

func resetPlayButton() {
    print("resetPlayButtonCalled")
    // TODO: How do I get a hold of the button and change the title from outside playMP3?
}