MPMusicPlayerController.play() 在杀死 iOS 音乐应用程序后不起作用

Question

I have an app that allows you to search for the title of a song in the music library and play it. I play the selected song using this code:

func playSongByPersistentID(id: Int) { //id is the persistent id of chosen song
    let predicate = MPMediaPropertyPredicate(value: id, forProperty: MPMediaItemPropertyPersistentID)
    let songQuery = MPMediaQuery()
    songQuery.addFilterPredicate(predicate)

    if songQuery.items?.count < 1 {
        print("Could Not find song") // make alert for this
        return
    } else {
        print("gonna play \(songQuery.items?[0].title)")
    }

    musicPlayer.prepareToPlay()
    musicPlayer.setQueueWithItemCollection(songQuery.collections![0])
    musicPlayer.play()
}

The above function gets called in tableView(:didSelectRowAtIndexPath) . I have confirmed that the correct ID and song title is retrieved when a song is selected.

Here is my problem. If I go into my app and select a song to play after killing the iOS music app , the song does not play. If I then choose a different song , that different song plays no problem. If I choose the same song over and over again it never plays.

musicPlayer is a systemMusicPlayer declared in my class.

Is this an iOS bug? I have no idea what is going on.

Answer 1

Here is the workaround I found.

What it does is set a timer once I try to start playing the music. That timer calls a function that tests if the music is playing. If the music is playing, the timer is invalidated. If not, it re-queues the item I want to play (a collection of items in this example) and tries to play again.

I've pulled this code from my app and abstracted it, so it may not compile as is but hopefully it gets the point across. I'm going to file this bug with Apple (after creating a small sample project) and recommend you do the same.

func playMusic()
{    
    musicPlayer = MPMusicPlayerController.applicationMusicPlayer()

    musicPlayer.setQueueWithItemCollection(MPMediaItemCollection(items: songsForPlayingWithMusicPlayer))

    musicPlayer.play()

    testForMusicPlayingTimer = NSTimer.scheduledTimerWithTimeInterval(NSTimeInterval(1), target: self, selector: "testForMusicPlaying", userInfo: nil, repeats: false)
}

func testForMusicPlaying()
{
    if musicPlayer.playbackState != .Playing
    {
        testForMusicPlayingTimer.invalidate()

        musicPlayer = MPMusicPlayerController.applicationMusicPlayer()

        musicPlayer.setQueueWithItemCollection(MPMediaItemCollection(items: songsForPlayingWithMusicPlayer))

        musicPlayer.play()

        testForMusicPlayingTimer = NSTimer.scheduledTimerWithTimeInterval(NSTimeInterval(1), target: self, selector: "testForMusicPlaying", userInfo: nil, repeats: false)
    }
    else
    {
        testForMusicPlayingTimer.invalidate()     
    }
}