MPNowPlayingInfoCenter 抛出 EXC_BAD_ACCESS

Question

我正在制作一个播放音频的应用程序，我已经设置它以便通过 MPNowPlayingInfoCenter 更新锁定屏幕，但我运行遇到了问题。

在看似随机的时间，我在尝试更新正在播放的信息时收到 EXC_BAD_ACCESS 错误。

这是这样做的代码：

- (void)updatePlayback
{
    if(!active)
        return;

    NowPlayingController* npc = [AudioController nowPlayingController];
    CMTime elapsed = player.currentTime;
    Float64 elInterval = CMTimeGetSeconds(elapsed);
    [npc setElapsed:elInterval];

    CMTime duration = player.currentItem.duration;
    Float64 durInterval = CMTimeGetSeconds(duration);
    [npc setRemaining:ceilf(durInterval - elInterval)];

    [npc setPlayPauseValue:isPlaying];
    if(durInterval > 0)
    {
        [npc setProgressValue:elInterval/durInterval];
        [npc setAudioDuration:durInterval];
    }

    _activeMetadata[MPMediaItemPropertyPlaybackDuration] = @(durInterval);
    _activeMetadata[MPNowPlayingInfoPropertyPlaybackRate] = @(isPlaying);
    _activeMetadata[MPNowPlayingInfoPropertyElapsedPlaybackTime] = @(elInterval);

    MPNowPlayingInfoCenter* npInfoCenter = [MPNowPlayingInfoCenter defaultCenter];
    if(npInfoCenter && _activeMetadata)
    {
        if([npInfoCenter respondsToSelector:@selector(setNowPlayingInfo:)])
        {

//////////THE FOLLOWING LINE TRIGGERS EXC_BAD_ACCESS SOMETIMES////////////
            [npInfoCenter setNowPlayingInfo:_activeMetadata];
        }

    }
}

99.9% 的情况下，这是有效的，但有时当将应用程序退出后台或更改音频文件时，或者只是随机地，

[npInfoCenter setNowPlayingInfo:_activeMetadata];

抛出 EXC_BAD_ACCESS.

此外，_activeMetadata 声明为：

@property (atomic, strong, retain) NSMutableDictionary* activeMetadata;

创建AVPlayer时实例化：

    AVAsset* asset = [AVAsset assetWithURL:[NSURL fileURLWithPath:path]];
    AVPlayerItem* playerItem = [AVPlayerItem playerItemWithAsset:asset];
    player = [AVPlayer playerWithPlayerItem:playerItem];

    CMTime duration = player.currentItem.duration;
    NSTimeInterval durInterval = CMTimeGetSeconds(duration);
    NSLog(@"%f", durInterval);

    MPMediaItemArtwork* albumArtwork = [[MPMediaItemArtwork alloc] initWithImage:[downloader useCachedImage:CacheKeySeriesBanners withName:nil withURL:info[@"image"]]];
    NSDictionary* nowPlayingInfo = @{MPMediaItemPropertyTitle:ptString,
                                     MPMediaItemPropertyArtist:spString,
                                     MPMediaItemPropertyArtwork:albumArtwork,
                                     MPMediaItemPropertyAlbumTitle:info[@"title"],
                                     MPMediaItemPropertyPlaybackDuration:@(durInterval),
                                     MPNowPlayingInfoPropertyPlaybackRate:@(1),
                                     MPNowPlayingInfoPropertyElapsedPlaybackTime:@(0)};
    [[MPNowPlayingInfoCenter defaultCenter] setNowPlayingInfo:nowPlayingInfo];

    _activeMetadata = [nowPlayingInfo mutableCopy];

updatePlayback 在每一帧上通过 CADisplayLink 调用。

知道是什么导致了异常吗？

Answer 1

我觉得你打电话给 setNowPlayingInfo 太频繁了。当然，它确实不应该崩溃，但没有必要使用 CADisplayLink 每秒调用它 60 次。

那你为什么这么频繁地调用它？如果是为了让进度条顺畅跟踪，还是没必要。来自 MPNowPlayingInfoPropertyElapsedPlaybackTime 声明：

// The elapsed time of the now playing item, in seconds.
// Note the elapsed time will be automatically extrapolated from the previously 
// provided elapsed time and playback rate, so updating this property frequently
// is not required (or recommended.)

p.s。我用 m4a 文件尝试了代码，发现 durInterval 是 NotANumber。在正确的持续时间和仅调用 setNowPlayingInfo 一次的情况下，进度条跟踪良好并且没有崩溃。

Answer 2

Apple 在 iOS 10.3 及更高版本中修复了此崩溃。因此，如果您想支持 iOS 10.2.1 及更低版本，请务必限制设置 [MPNowPlayingInfoCenter defaultCenter].nowPlayingInfo 属性的频率。也许限制设置属性每秒一次。

MPNowPlayingInfoCenter 抛出 EXC_BAD_ACCESS

MPNowPlayingInfoCenter throwing EXC_BAD_ACCESS

objective-c

avfoundation

ios

mpnowplayinginfocenter