cocoa - 无法无限循环播放 mp3 文件

Question

我正在尝试播放带有永恒循环的音乐文件。我的代码是：

NSString *path = [[NSBundle mainBundle] pathForResource:@"theme" ofType:@"mp3" inDirectory:@"assets/audios" ];
NSURL *url = [NSURL fileURLWithPath:path];

NSError *error;
AVAudioPlayer *audioPlayer = [[AVAudioPlayer alloc] initWithContentsOfURL:url error:&error];
audioPlayer.numberOfLoops = -1;
audioPlayer.volume = 1.0;
if (audioPlayer == nil){
    NSLog(@"Error creating player: %@", error);
}
[audioPlayer prepareToPlay];
[audioPlayer play];

但它什么也没做。不播放任何内容并打印任何消息日志。

下面的代码效果很好：

NSString *path = [[NSBundle mainBundle] pathForResource:@"theme" ofType:@"mp3" inDirectory:@"assets/audios" ];
NSURL *url = [NSURL fileURLWithPath:path];
SystemSoundID soundID;
AudioServicesCreateSystemSoundID((CFURLRef)CFBridgingRetain(url), &soundID);
AudioServicesPlaySystemSound (soundID);

但我需要控制音量和循环。

我不知道我做错了什么。谁能帮我？