第十一篇、UITableView headerview下拉放大

-(void)createTableViewHeaderView{


    _tableViewHeaderView = [[UIView alloc] initWithFrame:(CGRectMake(0, 0, ScreenWidth, _imageHeight))];
    _headerBackView = [[UIImageView alloc] init];

//    背景图
    _headerBackView.frame = CGRectMake(0, 0, ScreenWidth, _imageHeight);
    _headerBackView.image = [UIImage imageNamed:@"bj1@2x.jpg"];

    [_tableViewHeaderView addSubview:_headerBackView];
    _photoImageView = [[UIImageView alloc] initWithFrame:CGRectMake((ScreenWidth - 62)/2, 15 , 62 , 62 )];
    [self.tableViewHeaderView addSubview:self.photoImageView];
    _photoImageView.layer.cornerRadius = 31 ;
    _photoImageView.layer.masksToBounds = YES;

    _photoImageView.image = [UIImage imageNamed:@"2.jpg"];

    _userNameLabel = [[UILabel alloc] initWithFrame:CGRectMake(0, _photoImageView.frame.origin.y + _photoImageView.frame.size.height + 8 , ScreenWidth, 20 )];
    _userNameLabel.font = [UIFont fontWithName:@"iconfont" size:16 ];
    _userNameLabel.text = @"纳兰性德";
    _userNameLabel.textAlignment = 1;
    _userNameLabel.font = [UIFont systemFontOfSize:16  ];
    _userNameLabel.textColor = [UIColor whiteColor];
    [_tableViewHeaderView addSubview:self.userNameLabel];

    _introduceLabel = [[UILabel alloc] initWithFrame:CGRectMake((ScreenWidth - 229 )/2, _userNameLabel.frame.origin.y + _userNameLabel.frame.size.height + 10 , 229 , 16 )];
    _introduceLabel.alpha = .7;
    _introduceLabel.text = @"人生若只如初见，何事秋风悲画扇";
    _introduceLabel.textAlignment = 1;
    _introduceLabel.font = [UIFont systemFontOfSize:12 ];
    _introduceLabel.textColor = _userNameLabel.textColor;
    [_tableViewHeaderView addSubview:self.introduceLabel];

    self.tableView.tableHeaderView = _tableViewHeaderView;

}

- (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
    if (yOffset < 0) {
        CGFloat totalOffset = _imageHeight + ABS(yOffset);
        CGFloat f = totalOffset / _imageHeight;
        self.headerBackView.frame =  CGRectMake(- (width * f - width) / 2, yOffset, width * f, totalOffset); //拉伸后的图片的frame应该是同比例缩放。
    }


}