ios - 如何使用 AvAudioPlayer 实现 MPNowPlayingInfoCenter

Question

我正在为一个可以播放各种音轨的客户端创建一个 iOS 移动应用程序。

我想要实现的功能之一是在锁定屏幕和横幅上显示有关当前正在播放的音轨的信息。这是移动用户的简单便利之一，如果您的应用程序具有背景音频播放功能，这是必不可少的。就个人而言，我一直使用这个功能！

Answer 1

你应该首先像这样观察AVPlayerItem：AVAudioPlayer

[playerItem addObserver:self forKeyPath:@"timedMetadata" options:NSKeyValueObservingOptionNew context:nil];

然后创建一些全局变量：

NSString *title;
NSString *artist;
UIImage *artwork;

然后，您可能需要如下所示的功能，因此您可以观察关键路径timedMetadata并通过updateInfoCenterWithTitle:andArtist:andCover:.

- (void)observeValueForKeyPath:(NSString *)keyPath ofObject:(id)object change:(NSDictionary  *)change context:(void *)context
{
    if ([keyPath isEqualToString:@"timedMetadata"])
    {
        for (int i = 0; i < [audioPlayer.currentItem.timedMetadata count]; i++)
        {
            AVMetadataItem *metaData = [audioPlayer.currentItem.timedMetadata objectAtIndex:i];

            if ([[metaData commonKey] isEqualToString:AVMetadataCommonKeyArtist]) {
                artist = (NSString *)metaData.value;
            }
            else if ([[metaData commonKey] isEqualToString:AVMetadataCommonKeyTitle])
            {
                title = (NSString *)metaData.value;
                [self updateInfoCenterWithTitle:title andArtist:artist andCover:artwork];
            }
            else if ([[metaData commonKey] isEqualToString:AVMetadataCommonKeyArtwork])
            {
                if ([metaData.keySpace isEqualToString:AVMetadataKeySpaceID3])
                {
                    NSDictionary *dictionary = [metaData.value copyWithZone:nil];
                    artwork = [UIImage imageWithData:[dictionary objectForKey:@"data"]]];
                } else if ([metaData.keySpace isEqualToString:AVMetadataKeySpaceiTunes]) {
                    artwork = [UIImage imageWithData:[metaData.value copyWithZone:nil]];
                }
            }
            else {
                NSLog(@"%@ --> %@", [metaData commonKey], metaData.value);
            }
        }
    }
}

这就是魔法发生的地方：

- (void)updateInfoCenterWithTitle:(NSString *)title andArtist:(NSString *)artist andCover:(UIImage *)cover
{
    if (cover == nil) {
        cover = [UIImage imageNamed:@"defaultCover"];
    }

    MPNowPlayingInfoCenter *infoCenter = [MPNowPlayingInfoCenter defaultCenter];
    [infoCenter setNowPlayingInfo:@{MPMediaItemPropertyTitle:title,
                                    MPMediaItemPropertyArtist:artist,
                                    MPMediaItemPropertyArtwork:[[MPMediaItemArtwork alloc] initWithImage:cover]}];
}