xcode - MPNowPlayingInfoCenter info is not displayed on iOS 8

问题

I'm developing a music application, which should play music in the background.

I use the MPMoviePlayerController to play the music. My code to initiate the MPMoviePlayerController:

NSString* resourcePath = [[NSBundle mainBundle] resourcePath];
resourcePath = [resourcePath stringByAppendingString:@"/music.m4a"];
NSError* err;
self.player = [[MPMoviePlayerController alloc] initWithContentURL:[NSURL fileURLWithPath:resourcePath]];
if (err) {
    NSLog(@"ERROR: %@", err.localizedDescription);
}
AVAudioSession *session = [AVAudioSession sharedInstance];
[session setCategory:AVAudioSessionCategoryPlayback withOptions:AVAudioSessionCategoryOptionMixWithOthers error:nil];
[session setActive:YES error:nil];
[[UIApplication sharedApplication] beginReceivingRemoteControlEvents];
[self.player setShouldAutoplay:NO];
[self.player setControlStyle: MPMovieControlStyleEmbedded];
self.player.view.hidden = YES;
[self.player prepareToPlay];

When I execute [self.player play]; the music starts. But I also want to display the name of the song, the name of the album and the album artwork in the LockScreen and the ControlCenter. I'm using the following code:

Class playingInfoCenter = NSClassFromString(@"MPNowPlayingInfoCenter");
    if (playingInfoCenter) {
        NSMutableDictionary *songInfo = [[NSMutableDictionary alloc] init];
        MPMediaItemArtwork *albumArt = [[MPMediaItemArtwork alloc] initWithImage: [UIImage imageNamed:@"artwork.png"]];
        [songInfo setObject:@"SongName" forKey:MPMediaItemPropertyTitle];
        [songInfo setObject:@"ArtistName" forKey:MPMediaItemPropertyArtist];
        [songInfo setObject:@"AlbumTitle" forKey:MPMediaItemPropertyAlbumTitle];
        [songInfo setObject:albumArt forKey:MPMediaItemPropertyArtwork];
        [[MPNowPlayingInfoCenter defaultCenter] setNowPlayingInfo:songInfo];
    }

But nothing gets displayed in the LockScreen. It doesn't get displayed in the ControlCenter either.

How can I solve my problem? I didn't find anything on the internet.

Thanks in advance, Fabian.

回答1:

The problem is that you are not satisfying the requirements to become master of the lock screen and control center, as I explain in my book. You should be seeing the modern (iOS 8) equivalent of this:

The fact that you are not seeing it suggests that you are omitting one or more of the requirements, which I list (quoting directly from my book here):

• Your app must contain a UIResponder in its responder chain that returns YES from canBecomeFirstResponder, and that responder must actually be first responder.
• Some UIResponder in the responder chain, at or above the first responder, must implement remoteControlReceivedWithEvent:.
• Your app must call the UIApplication instance method beginReceivingRemoteControlEvents.
• Your app’s audio session’s policy must be Playback.
• Your app must be emitting some sound.

I don't know which of those you are omitting; it could be more than one. You might like to compare your code with a working example, here:

https://github.com/mattneub/Programming-iOS-Book-Examples/blob/master/iOS7bookExamples/bk2ch14p653backgroundPlayerAndInterrupter/backgroundPlayer/backgroundPlayer/ViewController.m

回答2:

Want to expand @matt's answer - setting nowPlayingInfo is useless when you use AVAudioSessionCategoryOptionMixWithOthers option.

回答3:

Expanding further on @matt's answer, it's required that you call endReceivingRemoteControlEvents and resignFirstResponder when the app comes back into the foreground (applicationDidBecomeActive). Otherwise the OS assumes you are a bad actor (or forgot to turn them off) and turns off your ability to show the sleep controls entirely, even after you call beginReceivingRemoteControlEvents again. I added these calls and now the Sleep Controls always show when they should.

回答4:

Want to explain @zakhej's answer - what's happens when set AVAudioSessionCategoryOptionMixWithOthers.

1. MPNowPlayingInfoCenter is a singleton, which means can only one application set it.
2. AVAudioSession is shared with other apps, every app can set it.

so. when you set category AVAudioSessionCategoryAmbient, AVAudioSessionCategoryPlayAndRecord and mix with others, AVAudioSessionCategoryPlayback and mix with others, setting MPNowPlayingInfoCenter's nowPlayingInfo is useless.

来源：https://stackoverflow.com/questions/30083862/xcode-mpnowplayinginfocenter-info-is-not-displayed-on-ios-8