iOS - AVAudioPlayer doesn't continue to next song while in background

Question

So I have an app that plays a bunch of songs while the user can flip through a comic book. I use AVAudioPlayer and I have it set up to play the songs in a set order. So wh

Answer 1

OS X exhibits the same problem using AVAudioPlayer, however UIApplication is an iOS-only construct. OS X requires using NSApplication instead, but NSApplication doesn't return until the application is terminating so we need to use threads. As a bonus, there's an assert() somewhere in the depths of NSApplication that demands the main thread.

This hybrid C++/Objective C function is one workaround for this OS X issue:

void do_the_dumb (void real_application(void)) {
    std::thread thread ([real_application]() {
        real_application();
        [[NSApplication sharedApplication] terminate: [NSApplication sharedApplication]];
    });
    [[NSApplication sharedApplication] run];
    thread.join();
};

Answer 2

Relevant discussion

SHORT ANSWER:

You need this code in either your first view controller's init or viewDidLoad method:

[[UIApplication sharedApplication] beginReceivingRemoteControlEvents];

---

LONG ANSWER W/ SAMPLE:

Here is my example. Like you, I began with an app that would play music in the background but could never continue playing after the first clip ended. I made a copy of the original Music.mp3 and named it Music2.mp3. My intention was to play Music2.mp3 as soon as Music.mp3 ended (audioPlayerDidFinishPlaying:). I goofed around with the background tasks for awhile until I got this working WITHOUT the background task:

-(id)init{
    self = [super initWithNibName:@"MediaPlayerViewController" bundle:nil];
    if(self){

        //Need this to play background playlist
        [[UIApplication sharedApplication] beginReceivingRemoteControlEvents];

        //MUSIC CLIP
        //Sets up the first song...
        NSString *musicPath = [[NSBundle mainBundle] pathForResource:@"Music" ofType:@"mp3"];
        if(musicPath){
            NSURL *musicURL = [NSURL fileURLWithPath:musicPath];
            audioPlayer = [[AVAudioPlayer alloc] initWithContentsOfURL:musicURL error:nil]; 
            [audioPlayer setDelegate:self];
        }
    }
    return self;
}


-(IBAction)playAudioFile:(id)sender{

    if([audioPlayer isPlaying]){
        //Stop playing audio and change test of button
        [audioPlayer stop];
        [sender setTitle:@"Play Audio File" forState:UIControlStateNormal];
    }
    else{
        //Start playing audio and change text of button so
        //user can tap to stop playback
        [audioPlayer play];
        [sender setTitle:@"Stop Audio File" forState:UIControlStateNormal];
    }
}


-(void)audioPlayerDidFinishPlaying:(AVAudioPlayer *)player successfully:(BOOL)flag{
    [audioButton setTitle:@"Play Audio File" forState:UIControlStateNormal];
    [playRecordingButton setTitle:@"Play Rec File" forState:UIControlStateNormal];

    //PLAY THE SECOND SONG
    NSString *musicPath2 = [[NSBundle mainBundle] pathForResource:@"Music2" ofType:@"mp3"];
    if(musicPath2){

        NSURL *musicURL2 = [NSURL fileURLWithPath:musicPath2];
        audioPlayer = [[AVAudioPlayer alloc] initWithContentsOfURL:musicURL2 error:nil];
        [audioPlayer setDelegate:self];
        NSLog(@"Play it again: \n%@", musicPath2);
        [audioPlayer play];
    } 
}

The end result is that my app is now playing Music2.mp3 on a continuous loop, even if the app is in the background.

Answer 3

Just to confirm what Squatch said, this is also the solution in Swift:

UIApplication.sharedApplication().beginReceivingRemoteControlEvents()