iOS TableView头视图根据偏移量下拉缩放效果

//========== 头视图创建与设置 ===========
  imageHight = 250;
  [self creatHeardView];

- (void)creatHeardView
{
  headerView = [[UIView alloc] initWithFrame:(CGRectMake(0, 0, ScreenWidth, imageHight+50))];
  //背景视图
  heardImageView = [[UIImageView alloc] init];
  heardImageView.frame = CGRectMake(0, 0, ScreenWidth, imageHight);
  heardImageView.image = [UIImage imageNamed:@"backGround.jpg"];
  [headerView addSubview:heardImageView];
  //用户头像
  personImageView = [[UIImageView alloc] initWithFrame:CGRectMake(ScreenWidth-30-60, imageHight-30, 60, 60)];
  personImageView.layer.cornerRadius = CGRectGetWidth(personImageView.frame)/2;
  personImageView.layer.masksToBounds = YES;
  [headerView addSubview:personImageView];
  //用户名
  personNameLabel = [[UILabel alloc] initWithFrame:CGRectMake(CGRectGetMinX(personImageView.frame)-200, CGRectGetMinY(personImageView.frame), 180, 30)];
  personNameLabel.font = [UIFont systemFontOfSize:15];
  personNameLabel.textColor = [UIColor whiteColor];
  personNameLabel.textAlignment = NSTextAlignmentRight;
  [headerView addSubview:personNameLabel];
  //个人签名
  introduceLabel = [[UILabel alloc] initWithFrame:CGRectMake(30, CGRectGetMaxY(personImageView.frame), ScreenWidth-60, 20)];
  introduceLabel.font = [UIFont systemFontOfSize:10];
  introduceLabel.textColor = [UIColor grayColor];
  introduceLabel.textAlignment = NSTextAlignmentRight;
  [headerView addSubview:introduceLabel];
  
  comTableView.tableHeaderView = headerView;//设置头视图
}

然后在TableView的滚动代理中有一个方法可以实时监测滚动偏移量，
#pragma mark - 滚动代理
- (void)scrollViewDidScroll:(UIScrollView *)scrollView
{
  CGFloat width = self.view.frame.size.width; // 图片宽度
  CGFloat yOffset = scrollView.contentOffset.y; // 偏移的y值，还要考虑导航栏的64哦
  if (yOffset < 0) {//向下拉是负值，向上是正
    CGFloat totalOffset = imageHight + ABS(yOffset);
    CGFloat f = totalOffset / imageHight;//缩放比例
    //拉伸后的图片的frame应该是同比例缩放。
    heardImageView.frame = CGRectMake(- (width * f - width) / 2, yOffset, width * f, totalOffset); 
  }
}