iOS - updating the media play/pause state in the m

问题:

We have a working app that uses an AU graph - CoreAudio API - to play audio. The graph is always running, and the play/pause state of the various source material is managed in the graph rendering callback functions. We successfully respond to UIEventTypeRemoteControl events, and we successfully update the lock-screen with the meta-data for the currently playing content using MPNowPlayingInfoCenter.

The one missing piece is to update the state of the play/pause button in the iOS multitasking bar. It is always in the "pause" (||) mode, even when the app audio is already paused. It never switches to its "play" (>) state.

Which API is used to update the play/pause button state?

回答1:

I figured out that when using a CoreAudio AU graph, AUGraphStart() will display the playback indicator in the iOS status bar and the iOS multitasking bar, and AUGraphStop() will clear them.

回答2:

Change MPNowPlayingInfo dictionary, set new parameter

MPNowPlayingInfoPropertyPlaybackRate to 1.0f to show pause button

MPNowPlayingInfoPropertyPlaybackRate to 0.0f to show play button

From play button - to - pause button

Class playingInfoCenter = NSClassFromString(@"MPNowPlayingInfoCenter");
if(playingInfoCenter) 
{       
    NSMutableDictionary *songInfo = [NSMutableDictionary dictionaryWithDictionary:[MPNowPlayingInfoCenter defaultCenter].nowPlayingInfo];
    //[songInfo setObject:songTitle forKey:MPMediaItemPropertyTitle];
    //[songInfo setObject:songArtist forKey:MPMediaItemPropertyArtist];
    [songInfo setObject:[NSNumber numberWithFloat:1.0f] forKey:MPNowPlayingInfoPropertyPlaybackRate];
    [MPNowPlayingInfoCenter defaultCenter].nowPlayingInfo = songInfo;            
 }

From pause button - to - play button

Class playingInfoCenter = NSClassFromString(@"MPNowPlayingInfoCenter");
if(playingInfoCenter) 
{         
    NSMutableDictionary *songInfo = [NSMutableDictionary dictionaryWithDictionary:[MPNowPlayingInfoCenter defaultCenter].nowPlayingInfo];
    //[songInfo setObject:songTitle forKey:MPMediaItemPropertyTitle];
    //[songInfo setObject:songArtist forKey:MPMediaItemPropertyArtist];
    [songInfo setObject:[NSNumber numberWithFloat:0.0f] forKey:MPNowPlayingInfoPropertyPlaybackRate];
    [MPNowPlayingInfoCenter defaultCenter].nowPlayingInfo = songInfo;
}