ios - 检测原生iOS Music App中当前正在播放的歌曲信息

Question

我在本地 iOS 音乐应用程序中获取当前正在播放的歌曲信息(如(标题、艺术家...))时遇到了一些问题。

这是确切的问题，我的应用程序正在使用 MPMusicPlayerController与 iPodMusicPlayer这个属性是调用 myPlayer .当用户在我的应用程序中控制音乐时，我能够以这种方式显示当前的歌曲播放信息......

- (void)getTrackDescription {

    // getting whats currently playing
    self.nowPlayingItem = [myPlayer nowPlayingItem];

    // song title currently playing
    self.title = [self.nowPlayingItem valueForProperty:MPMediaItemPropertyTitle];

    // if title is not fund Unknown will be displayed
    if (title == (id)[NSNull null] || title.length == 0) {
        title = @"Unknown";
    }

    // artist currently playing
    self.artist = [self.nowPlayingItem valueForProperty:MPMediaItemPropertyArtist];

    // if artist is not fund Unknown will be displayed
    if (artist == (id)[NSNull null] || artist.length == 0) {
        artist = @"Unknown";
    }

    //[self.currentlyPlaying setLineBreakMode:NSLineBreakByWordWrapping];

    // displaying current artist and title song playing
    [self.currentlyPlaying setText:[NSString stringWithFormat:@"%@ - %@", artist, title]];
}

但是，当用户将应用程序留在后台或仅使用 时，就会出现问题。控制中心更改歌曲.. 如果用户继续使用控制中心或音乐应用程序本身，我的应用程序仍会显示以前的歌曲信息并且没有任何更新。

我试图以这种方式解决问题......

- (void)viewDidLoad {
    [super viewDidLoad];

    if (self.myPlayer.playbackState == MPMusicPlaybackStatePlaying || self.myPlayer.playbackState == MPMusicPlaybackStateSeekingForward || self.myPlayer.playbackState == MPMusicPlaybackStateSeekingBackward){
        // updating track name regardless the user uses app controllers or not
        [self getTrackDescription];
    } 
}

我什至尝试评论 if 条件以查看我是否以这种方式获取歌曲信息，但这是同样的问题。

好吧，我希望有人可以帮助我并解释我做错了什么..

提前致谢...!

更新

这就是我目前所拥有的...我的 getTrackDescription 逻辑是相同的，但签名更改为 - (void)getTrackDescription:(id)notification

- (void)viewWillAppear:(BOOL)animated{

    NSNotificationCenter *notificationCenter = [NSNotificationCenter defaultCenter];

    [notificationCenter addObserver:self
                           selector:@selector(getTrackDescription:)
                               name:MPMusicPlayerControllerPlaybackStateDidChangeNotification
                             object:self.myPlayer];
    [self.myPlayer beginGeneratingPlaybackNotifications];

}

-(void)viewWillDisappear:(BOOL)animated{

    [[NSNotificationCenter defaultCenter] removeObserver:self
                                               name:MPMusicPlayerControllerPlaybackStateDidChangeNotification
                                               object:self.myPlayer];
    [self.myPlayer endGeneratingPlaybackNotifications];
}

Answer 1

您要做的是将您的 View Controller 作为观察者添加到 MPMusicPlayerControllerNowPlayingItemDidChangeNotification每次音乐播放器中的轨道更改时都会调用通知，这听起来很重要。不要忘记使用以下方法指定播放器何时开始/结束生成这些通知。

[[MPMusicPlayerController iPodMusicPlayer] beginGeneratingPlaybackNotifications];
[[MPMusicPlayerController iPodMusicPlayer] endGeneratingPlaybackNotifications];