Ios 锁屏不支持nowPlayingInfo字典

我试图让我的播客应用程序在锁定屏幕上显示内容，同时尊重播放/暂停控制。这是我的密码：

- (void)playEpisodeAtIndex:(NSInteger)index {

    _currentIndex = index;
    TalkPodEpisode *episode = self.playlist[index];
    self.player = [[AVPlayer alloc] initWithURL:episode.url];
    [self.player play];
    _playing = YES;

    [[UIApplication sharedApplication] beginReceivingRemoteControlEvents];

    NSDictionary *lockScreenInfo = @{MPMediaItemPropertyTitle:self.currentEpisode.title,
                                 MPMediaItemPropertyArtist: @"The Talk Pod",
                                 MPNowPlayingInfoPropertyPlaybackRate:[NSNumber numberWithDouble:self.player.rate],
                                          MPNowPlayingInfoPropertyElapsedPlaybackTime:[NSNumber numberWithDouble:[self currentPlaybackTime]]};
    [MPNowPlayingInfoCenter defaultCenter].nowPlayingInfo = lockScreenInfo;


}

奇怪的是，发生了这样的事情：

响应和处理事件工作正常

艺术家和标题显示在锁定屏幕上

进度滑块显示--:--并且不显示播放进度

这一集的持续时间也不会出现

以下是获取当前运行时间的代码：

- (NSTimeInterval)currentPlaybackTime {

    CMTime time = self.player.currentTime;
    if (CMTIME_IS_VALID(time)) {

        return time.value/time.timescale;

    }

    return 0;

}

以下是切换播放和暂停的代码：

- (void)playPause {

    if (self.player) {

        if (_playing) {

            [self.player pause];
            _playing = NO;

        } else {

            [self.player play];
            _playing = YES;

        }

        NSMutableDictionary *lockScreenInfo = [[MPNowPlayingInfoCenter defaultCenter].nowPlayingInfo mutableCopy];
        lockScreenInfo[MPNowPlayingInfoPropertyPlaybackRate] = [NSNumber numberWithDouble:self.player.rate];
        lockScreenInfo[MPNowPlayingInfoPropertyElapsedPlaybackTime] = [NSNumber numberWithDouble:[self currentPlaybackTime]];
        [MPNowPlayingInfoCenter defaultCenter].nowPlayingInfo = lockScreenInfo;

    }

}

---

有人知道怎么解决这个问题吗？让我困惑的是，屏幕上显示了一些内容，但当前的播放信息却没有。同样，接收和处理事件工作正常。

可能需要在nowPlayingInfo字典中设置播放持续时间键。 另一个问题请看我的帖子，它在我的应用程序中运行良好。