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标题: ios - MPNowPlayingInfoCenter 抛出 EXC_BAD_ACCESS [打印本页]

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作者: 菜鸟教程小白    时间: 2022-12-12 22:10
标题: ios - MPNowPlayingInfoCenter 抛出 EXC_BAD_ACCESS

我正在制作一个播放音频的应用程序，我已经对其进行了设置，以便通过 MPNowPlayingInfoCenter 更新锁定屏幕，但我遇到了问题。

在尝试更新正在播放的信息时，有时会出现 EXC_BAD_ACCESS 错误。

这是执行此操作的代码:

- (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 respondsToSelectorselector(setNowPlayingInfo])
        {

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

    }
}

99.9% 的情况下，这是可行的，但有时在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。

另外，_activeMetadata 被声明为:

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

在创建 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 在每一帧通过 CADisplayLink 调用。

任何想法可能导致异常？

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Best Answer-推荐答案

我认为您过于频繁地调用 setNowPlayingInfo。当然，它确实不应该崩溃，但没有必要使用 CADisplayLink 每秒调用 60 次。

那你为什么这么频繁地调用它？如果是因为你想让进度条跟踪流畅，还是没有必要的。从 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.)

附言我用 m4a 文件尝试了代码，发现 durInterval 是 NotANumber。使用正确的持续时间并仅调用一次 setNowPlayingInfo，进度条跟踪良好且没有崩溃。

关于ios - MPNowPlayingInfoCenter 抛出 EXC_BAD_ACCESS，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/39555416/

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