iOS - AVAudioPlayer不会在后台继续播放下一首歌曲

Question

因此，我有一个应用程序，播放一串歌曲，而用户可以翻阅漫画书。我使用AVAudioPlayer，并且设置了按照设定的顺序播放歌曲。所以当一首歌完成时，下一首将会播放。当应用程序打开时，此功能完美无瑕。当应用程序在后台时发生问题。我将应用程序设置为在后台播放，而且工作正常。所以当用户按下主屏幕时，音乐继续播放。问题发生在歌曲结束时，它应该像打开应用时播放下一首歌一样。相反没有任何反应根据我的NSLog语句正确的方法被调用，但没有任何反应。这是我的代码：

- (void)audioPlayerDidFinishPlaying: (AVAudioPlayer *)player successfully: (BOOL) flag { 

NSLog(@"Song finished"); 

if ([songSelect isEqualToString: @"01icecapades"]) { 
    isPlay = @"yes"; 
    songSelect = @"02sugarcube"; 
    imageSelect = @"playbanner02"; 
    [self performSelector:@selector(triggerSong) withObject:nil afterDelay:0]; 
    [self performSelector:@selector(triggerBanner) withObject:nil afterDelay:0]; 
} 
else if ([songSelect isEqualToString: @"02sugarcube"]) { 
    isPlay = @"yes"; 
    songSelect = @"03bullets"; 
    imageSelect = @"playbanner03"; 
    [self performSelector:@selector(triggerSong) withObject:nil afterDelay:0]; 
    [self performSelector:@selector(triggerBanner) withObject:nil afterDelay:0]; 
} 
else if ([songSelect isEqualToString: @"03bullets"]) { 
    isPlay = @"yes"; 
    songSelect = @"04satanama"; 
    imageSelect = @"playbanner04"; 
    [self performSelector:@selector(triggerSong) withObject:nil afterDelay:0]; 
    [self performSelector:@selector(triggerBanner) withObject:nil afterDelay:0]; 
} 
else if ([songSelect isEqualToString: @"04satanama"]) { 
    isPlay = @"yes"; 
    songSelect = @"05uglyjoke"; 
    imageSelect = @"playbanner05"; 
    [self performSelector:@selector(triggerSong) withObject:nil afterDelay:0]; 
    [self performSelector:@selector(triggerBanner) withObject:nil afterDelay:0]; 
} 
else if ([songSelect isEqualToString: @"05uglyjoke"]) { 
    isPlay = @"yes"; 
    songSelect = @"01icecapades"; 
    imageSelect = @"playbanner01"; 
    [self performSelector:@selector(triggerSong) withObject:nil afterDelay:0]; 
    [self performSelector:@selector(triggerBanner) withObject:nil afterDelay:0]; 
}} 

上面是识别哪首歌正在播放，然后设置正确的歌曲的代码。然后触发另一种设置播放器的方法。

- (void)triggerSong { 
NSLog(@"triggerSong called"); 
NSString  *path; 
NSError  *error; 
// Path the audio file 
path = [[NSBundle mainBundle] pathForResource:songSelect ofType:@"mp3"]; 
// If we can access the file... 
if ([[NSFileManager defaultManager] fileExistsAtPath:path]) 
{  
    // Setup the player 
    player = [[AVAudioPlayer alloc] initWithContentsOfURL:[NSURL fileURLWithPath:path] error:&error]; 
    //player = [initWithContentsOfURL:[NSURL fileURLWithPath:path] error:&error]; 
    [player setDelegate: self]; 
    // Set the volume (range is 0 to 1) 
    player.volume = 1.0f;  
    [player prepareToPlay]; 
    [player setNumberOfLoops:0]; 
    [player play]; 
    NSLog(@"player play"); 
    [error release]; 
    player.delegate = self; 
    // schedules an action every second for countdown 
    [NSTimer scheduledTimerWithTimeInterval:0.5 target:self selector:@selector(updateTimeLeft) userInfo:nil repeats:YES]; 
}} 

现在我假设这不是最好的方式来做到这一点，但它应用程序处于前景状态时效果很好。我一直在查看文档，我似乎无法找到造成这个问题的原因。我希望有人能够看到我的方法有错误。就像我之前说过的，triggerSong方法中的两个NSLogs被调用，所以我不明白为什么AVAudioPlayer（播放器）没有被调用。

我也有我的info.plist正确的设置，我有这个在我viewDidLoad中：

//Make sure the system follows our playback status 
[[AVAudioSession sharedInstance] setCategory:AVAudioSessionCategoryPlayback error:nil]; 
[[AVAudioSession sharedInstance] setActive: YES error: nil]; 

感谢任何见解。非常感激。

Answer 1

Relevant discussion

简短的回答：

你需要这个代码或者您的第一个视图控制器的初始化或viewDidLoad方法：

[[UIApplication sharedApplication] beginReceivingRemoteControlEvents]; 

---

长的答案W /示例：

这是我的例子。和你一样，我从一个可以在后台播放音乐的应用程序开始，但在第一个剪辑结束之后无法继续播放。我制作了原始Music.mp3的一个副本，并将其命名为Music2.mp3。我的意图是在Music.mp3结束后立即播放Music2.mp3（audioPlayerDidFinishPlaying :)。我与后台任务疯玩了一段时间，直到我得到这个工作没有后台任务：

-(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]; 
    } 
} 

最终的结果是，我的应用程序现在开始连续循环播放Music2.mp3，即使该应用程序是的背景。

Answer 2

只是为了确认哪些Squatch说，这也是雨燕的解决方案：

UIApplication.sharedApplication().beginReceivingRemoteControlEvents() 

Answer 3

OS X使用表现出的AVAudioPlayer同样的问题，但是UIApplication的是一款iOS只构建。 OS X需要使用NSApplication，但NSApplication不会返回，直到应用程序终止，因此我们需要使用线程。作为奖励，在NSApplication的深处有一个assert（）需要主线程。

这种混合C++/Objective C的功能是为这个OS X的问题，一个解决办法：

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(); 
};