iOS - AVAudioPlayer 在后台不会继续播放下一首歌曲

Question

所以我有一个应用程序可以播放一堆歌曲，而用户可以翻阅一本漫画书。我使用 AVAudioPlayer 并将其设置为按固定顺序播放歌曲。因此，当一首歌曲结束时，下一首歌曲将播放。当应用程序打开时，这可以完美运行。当应用程序在后台时会出现问题。我将应用程序设置为在后台播放，效果很好。因此，当用户按下主屏幕时，音乐会继续播放。歌曲结束时会出现问题，假设像打开应用程序时一样播放下一首歌曲。相反，什么也没有发生。根据我的 NSLog 语句，正在调用正确的方法，但没有任何 react 。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];
}}

上面是识别正在播放哪首歌的代码，然后设置正确的歌曲。然后它触发另一个设置播放器的方法。

- (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法，但是当应用程序处于前台状态时它会很好。我一直在查看文档，但似乎无法找到导致此问题的原因。我希望有人能够看到我的方法有错误。就像我之前说的，正在调用 triggerSong 方法中的两个 NSLog，所以我看不出为什么没有调用 AVAudioPlayer(播放器)。

我的 info.plist 中也有正确的设置，并且我的 viewDidLoad 中有这个:

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

感谢您的任何见解。非常感激。

Answer 1

Relevant discussion

简短的回答:

您需要在第一个 View Controller 的 init 或 viewDidLoad 方法中使用此代码:

[[UIApplication sharedApplication] beginReceivingRemoteControlEvents];

带样本的长答案:

这是我的例子。和你一样，我开始使用一个可以在后台播放音乐但在第一个剪辑结束后无法继续播放的应用程序。我复制了原始 Music.mp3 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:)。我在后台任务中混了一段时间，直到我在没有后台任务的情况下完成了这项工作:

-(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];
    } 
}

最终结果是我的应用程序现在正在连续循环播放 Music2.mp3，即使应用程序在后台也是如此。