MPNowPlayingInfoCenter defaultCenter 不会更新或检索信息

Question

我正在努力更新 MPNowPlayingInfoCenter，但遇到了一些麻烦。我已经尝试了很多，以至于我不知所措。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];


    }

这个不行，我也试过了：

   [[MPNowPlayingInfoCenter defaultCenter] setNowPlayingInfo:nil];

试图让它从 iPod 应用程序中删除现有信息（或那里可能有信息的任何东西）。另外，为了看看能否找出问题所在，我尝试检索应用启动的当前信息：

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

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

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

我对此进行了相当多的研究，以下文章对此进行了非常彻底的解释，但是，我仍然无法使其正常工作。我错过了什么吗？会有什么干扰吗？这是我的应用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接收远程控制事件，只需添加此行即可解决问题：

 [[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YES？您是否在 plist 中设置了应用程序在后台键中播放音频？

- (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;

}