如何使用AvAudioPlayer实施MPNowPlayingInfoCenter

Question

I am in the midst of creating an iOS mobile app for a client that will play a variety of audio tracks.

One of the features that I wanted to implement was to display information about a currently-playing audio track on the lock screen and banner . This is one of those simple convenience to a mobile user and a must-have if your app has background audio playing. Personally, I use this feature all the time!

Answer 1

You should first observe the AVPlayerItem of AVAudioPlayer like so:

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

Then create some global variables:

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

You would then probably need a function like the one below, so you observe the key path timedMetadata and update the InfoCenter through 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);
            }
        }
    }
}

This is where the magic happens:

- (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]}];
}