//获得当前屏幕亮度
  light = [UIScreen mainScreen].brightness;
  light = 0.5f;
  //直接赋值或者使用set方法皆可
  [UIScreen mainScreen].brightness = light;

MPMusicPlayerController *mpVC = [MPMusicPlayerController applicationMusicPlayer];
//获得系统当前音量
voice = _mpVC.volume;
voice = 0.5f;
//改变系统音量
_mpVC.volume = voice;

- (void)leftSwipGes:(UIPanGestureRecognizer *)leftSwip
{
  //滑动方法获取到当前位置的y坐标
  leftCurrentY = [leftSwip translationInView:leftView].y;
  NSLog(@"left");
  //当前坐标大于上一次移动的坐标，为向下滑动
  if (leftCurrentY > leftLastY) {
    if (light > 0) {
      //向下滑动屏幕变暗，亮度下降
      light = light - 0.01;
    }
    else{
      //当亮度为0时固定为0，禁止为负值
      light = 0;
    }
  }
  else
  {
    if (light < 1) {
      //向上滑动亮度增加
      light = light + 0.01;
    }
    else{
      //当亮度为1时固定为1，禁止大于1
      light = 1;
    }
  }
  //设置屏幕亮度
  [UIScreen mainScreen].brightness = light;
  //当前位置的上一次移动的位置y坐标
  leftLastY = leftCurrentY;
}
//此处除参数外原理一样，不再额外注释
- (void)rightSwipGes:(UIPanGestureRecognizer *)rightSwip
{
  NSLog(@"right");
  rightCurrentY = [rightSwip translationInView:rightView].y;
  if (rightCurrentY > rightLastY) {
    if (voice > 0) {
      voice = voice - 0.01;
    }
    else{
      voice = 0;
    }
  }
  else
  {
    if (voice < 1) {
      voice = voice + 0.01;
    }
    else{
      voice = 1;
    }
  }
  //设置系统音量
  _mpVC.volume = voice;
  rightLastY = rightCurrentY;
}

//从budle路径下读取音频文件,这个文件名是你的歌曲名字,mp3是你的音频格式
  NSString *string = [[NSBundle mainBundle] pathForResource:@"夜空中最亮的星" ofType:@"mp3"];
  NSString *playUrl = [string stringByAddingPercentEscapesUsingEncoding:NSUTF8StringEncoding]; //转码成UTF-8 否则可能会出现错误
  //把音频文件转换成url格式
  NSURL *url = [NSURL URLWithString:playUrl];
  //初始化音频类 并且添加播放文件
  _avAudioPlayer = [[AVAudioPlayer alloc] initWithContentsOfURL:url error:nil];
  [[AVAudioSession sharedInstance] setCategory:AVAudioSessionCategoryPlayback error:nil];
  //设置初始音量大小
  _avAudioPlayer.volume = voice;
  //设置音乐播放次数 -1为一直循环
  _avAudioPlayer.numberOfLoops = -1;
  //预播放
  [_avAudioPlayer prepareToPlay];
  [_avAudioPlayer play];

 [[AVAudioSession sharedInstance] setCategory:AVAudioSessionCategoryPlayback error:nil];