无法使用AVQueuePlayer在iOS5的后台进行音频播放

我正在尝试构建一个应用程序来播放本地音乐，但不幸的是，我无法在iOS5中使用AVQueuePlayer在后台进行音频播放 .

在我的ViewDidLoad中，我得到了这段代码：

// Player setup
mAudioPlayer = [[AVQueuePlayer alloc] init];
[[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(playerItemDidReachEnd:) name:AVPlayerItemDidPlayToEndTimeNotification object:nil];
[mAudioPlayer addPeriodicTimeObserverForInterval:CMTimeMakeWithSeconds(1.0, 1) queue:NULL usingBlock:^(CMTime time) {
    [self updatePositionOnDisplay]; 
}];

// Audio session setup
NSError *setCategoryErr = nil;
NSError *activationErr  = nil;
[[AVAudioSession sharedInstance] setCategory: AVAudioSessionCategoryPlayback error: &setCategoryErr];
[[AVAudioSession sharedInstance] setActive: YES error: &activationErr];

这是我的“playerItemDidReachEnd”方法：

- (void)playerItemDidReachEnd:(NSNotification*)notification 
{
    NSLog(@"playerItemDidReachEnd");

    UIBackgroundTaskIdentifier newTaskID = [[UIApplication sharedApplication] beginBackgroundTaskWithExpirationHandler:^{
        [[UIApplication sharedApplication] endBackgroundTask:newTaskID];
    }];
    NSLog(@"playerItemDidReachEnd 2");

    NSLog(@"searching next song");
    mCurrentSong = [self getNextSongWithIsSwitched:NO];
    if(mCurrentSong != nil){
        NSLog(@"Start : %@ - %@", mCurrentSong.artist, mCurrentSong.title);

        mTapeTitle.text = [NSString stringWithFormat:@"%@ - %@", mCurrentSong.artist, mCurrentSong.title];

        AVPlayerItem* i = [[AVPlayerItem alloc] initWithURL:[NSURL URLWithString:mCurrentSong.path]];

        if(i != nil){
            [mAudioPlayer insertItem:i afterItem:nil];
        }else
            NSLog(@"BING!! no AVPlayerItem created for song's path: %@", mCurrentSong.path);

        [i release];
    }else{
        NSLog(@"no song found");
        [mAudioPlayer pause];
        isPlaying = NO;        
        [mPlayButton setSelected:NO];
    }

    [[UIApplication sharedApplication] endBackgroundTask:newTaskID];
    newTaskID = UIBackgroundTaskInvalid;
}

当我开始播放时，它可以工作，并在我关闭屏幕时继续播放 . 但是当歌曲结束时，这是日志

2012-03-01 10:00:27.342 DEMO[3096:707] playerItemDidReachEnd
2012-03-01 10:00:27.360 DEMO[3096:707] playerItemDidReachEnd 2
2012-03-01 10:00:27.363 DEMO[3096:707] searching next song
2012-03-01 10:00:27.381 DEMO[3096:707] Start : Moby - Ah-Ah

但没有一首歌有效地开始......

谁能告诉我我的代码有什么问题？

非常感谢 .