Geek Answers Handbook

IOS: MPMusicPlayerControllerPlaybackStateDidChangeNotification called multiple times on some devices

I have an application that plays music.

I use the following code to listen for playback status changes from MPMusicPlayerController to update the user interface. More precisely, I switch the appearance of the play button between play and pause.

NSNotificationCenter *notificationCenter = [NSNotificationCenter defaultCenter]; [notificationCenter addObserver: self selector: @selector (handle_NowPlayingItemChanged:) name: MPMusicPlayerControllerNowPlayingItemDidChangeNotification object: self.musicPlayer]; [notificationCenter addObserver: self selector: @selector (handle_PlaybackStateChanged:) name: MPMusicPlayerControllerPlaybackStateDidChangeNotification object: self.musicPlayer]; [self.musicPlayer beginGeneratingPlaybackNotifications];

This works great on iPod Touch (iOS 5) and iPhone 3GS (iOS 5) . Each time the playback state changes, I get the following callback:

 [JBMediaPlayer handle_PlaybackStateChanged:] :: playbackState: 1

where 1 means MPMusicPlaybackStatePlaying .

However, if I run the same on iPad 1 (iOS 5) , iPad 2 (iOS 5) or iPad 3 (iOS 6) I get the following sequence, and not just one callback:

 -[JBMediaPlayer handle_PlaybackStateChanged:] :: playbackState: 1 -[JBMediaPlayer handle_PlaybackStateChanged:] :: playbackState: 2 -[JBMediaPlayer handle_PlaybackStateChanged:] :: playbackState: 1 -[JBMediaPlayer handle_PlaybackStateChanged:] :: playbackState: 2

where 2 means MPMusicPlaybackStatePaused and causes my application to display an incorrect state in the user interface because the song is actually playing.

The funniest thing is that from time to time the sequence

 -[JBMediaPlayer handle_PlaybackStateChanged:] :: playbackState: 1 -[JBMediaPlayer handle_PlaybackStateChanged:] :: playbackState: 2 -[JBMediaPlayer handle_PlaybackStateChanged:] :: playbackState: 1 -[JBMediaPlayer handle_PlaybackStateChanged:] :: playbackState: 2 -[JBMediaPlayer handle_PlaybackStateChanged:] :: playbackState: 1

which ends correctly with 1 MPMusicPlaybackStatePlaying , however it still does not make sense that the callback is called 5 times with variable values.

Any ideas on how to solve this or suggest, what else can I check to narrow down the problem?

Since I have not received an answer yet, I also cross-posted the question on the Apple Developer Forum : https://devforums.apple.com/thread/158426

+4
source share
2 answers

I think this is the same error:

Invalid playback status in MP Music Player Controller in ios 5

I posted a workaround for the error in this question.

0
source

You can check the actual playback status using the currentPlaybackRate property. MPMusicPlaybackStatePaused must match a rate of 0.0. An example of how it can be implemented is shown below ...

 - (void)musicPlayerControllerPlaybackStateDidChangeNotification:(NSNotification *)notification { float playbackRate = [((MPMusicPlayerController *)notification.object) currentPlaybackRate]; MPMusicPlaybackState playbackState = (MPMusicPlaybackState)[notification.userInfo[@"MPMusicPlayerControllerPlaybackStateKey"] integerValue]; switch (playbackState) { case MPMusicPlaybackStatePaused: if (playbackRate <= .0f) { self.playbackState = playbackState; } break; default: self.playbackState = playbackState; break; } }

Thus, you can turn off the false pause notification.

0
source

More articles:


All Articles