MPNowPlayingInfoCenter defaultCenter不会更新或检索信息

Question

我正在更新MPNowPlayingInfoCenter，但遇到了一些麻烦。我试了相当多，到了不知所措的地步。以下是我的代码：

    self.audioPlayer.allowsAirPlay = NO;

    Class playingInfoCenter = NSClassFromString(@"MPNowPlayingInfoCenter");

    if (playingInfoCenter) {

        NSMutableDictionary *songInfo = [[NSMutableDictionary alloc] init];

        MPMediaItemArtwork *albumArt = [[MPMediaItemArtwork alloc] initWithImage:[UIImage imageNamed:@"series_placeholder"]];

        [songInfo setObject:thePodcast.title forKey:MPMediaItemPropertyTitle];
        [songInfo setObject:thePodcast.author forKey:MPMediaItemPropertyArtist];
        [songInfo setObject:@"NCC" forKey:MPMediaItemPropertyAlbumTitle];
        [songInfo setObject:albumArt forKey:MPMediaItemPropertyArtwork];

        [[MPNowPlayingInfoCenter defaultCenter] setNowPlayingInfo:songInfo];


    }

这不管用，我也试过了：

   [[MPNowPlayingInfoCenter defaultCenter] setNowPlayingInfo:nil];

试图让它从iPod应用程序(或任何可能有信息的应用程序)中删除现有信息。此外，为了看看我是否能找出问题所在，我尝试在应用程序启动时检索当前信息：

  NSDictionary *info = [[MPNowPlayingInfoCenter defaultCenter] nowPlayingInfo];
  NSString *title = [info valueForKey:MPMediaItemPropertyTitle];
  NSString *author = [info valueForKey:MPMediaItemPropertyArtist];

  NSLog(@"Currently playing: %@ // %@", title, author);

我得到了Currently playing: (null) // (null)

我已经对此进行了相当多的研究，下面的文章对它进行了相当彻底的解释，然而，我仍然无法让它正常工作。我是不是遗漏了什么？会有什么干扰吗？这是我的应用程序需要注册才能访问的服务吗(在任何文档中都没有看到)？

Apple's Docs

Change lock screen background audio controls

Now playing info ignored

Answer 1

我终于找到了问题所在，我没有提示我的应用程序接收远程控制事件，只需添加下面这行就解决了这个问题：

 [[UIApplication sharedApplication] beginReceivingRemoteControlEvents];

Answer 2

我使用下面的代码，它总是有效的。我也像你一样使用MPMoviePlayer。你检查过NSClassFromString(@"MPNowPlayingInfoCenter")是否真的返回过YES吗？你有没有设置你的应用程序播放音频在背景键你的plist？

- (void) loadMPInformation
{
    NSDictionary *mpInfo;

    if([savedTrack.belongingAlbum.hasAlbumArt boolValue] == NO){
        mpInfo = [NSDictionary dictionaryWithObjectsAndKeys:savedTrack.belongingAlbum.album, MPMediaItemPropertyAlbumTitle, 
                  savedTrack.belongingArtist.artist, MPMediaItemPropertyArtist, savedTrack.name, MPMediaItemPropertyTitle, nil];   
    } else {
        UIImage *artImage = [UIImage imageWithData:savedTrack.belongingAlbum.art];
        MPMediaItemArtwork *artwork = [[MPMediaItemArtwork alloc] initWithImage:artImage];
        mpInfo = [NSDictionary dictionaryWithObjectsAndKeys:savedTrack.belongingAlbum.album, MPMediaItemPropertyAlbumTitle, 
                  savedTrack.belongingArtist.artist, MPMediaItemPropertyArtist, savedTrack.name, MPMediaItemPropertyTitle, artwork, MPMediaItemPropertyArtwork, nil];
    }
    [MPNowPlayingInfoCenter defaultCenter].nowPlayingInfo = mpInfo;

}