AVAudioFile无法从文档目录中读取文件

NSArray * paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);
NSString * documentsDirectory = [paths objectAtIndex:0];
NSString *filePath = [NSString stringWithFormat:@"%@/audio.mp3",documentsDirectory];
NSURL *audioPathURL = [NSURL fileURLWithPath:filePath];
NSFileManager *filemanager = [[NSFileManager alloc]init];
    if ([filemanager fileExistsAtPath:filePath])
    {
AVAudioFile *audioFile = [[AVAudioFile alloc] initForReading:audioPathURL error:&err];
}
NSArray * paths = NSSearchPathForDirectoriesInD