一个方法搞定表头拉伸效果

自定义view，imageView附在view上，view做表头

viewdidLoad

static float headerHeght;   //图片高度
- (void)viewDidLoad {
    [super viewDidLoad];
    headerHeght = 100;
    self.automaticallyAdjustsScrollViewInsets = NO;
    _tab.delegate = self;
    _tab.dataSource = self;
    self.navigationItem.title = @"表头测试";
    // 表头自定义view
    UIView *headerVi = [[UIView alloc] initWithFrame:CGRectMake(0, 0, [UIScreen mainScreen].bounds.size.width, headerHeght)];
    // 填充表头imageView
    _headerIma = [[UIImageView alloc] initWithFrame:CGRectMake(0, 0, [UIScreen mainScreen].bounds.size.width, headerHeght)];
    _headerIma.image = [UIImage imageNamed:@"星空.jpeg"];
    [headerVi addSubview:_headerIma];
    _tab.tableHeaderView = headerVi;
    
}

滚动拉伸方法

- (void)scrollViewDidScroll:(UIScrollView *)scrollView
{
    CGFloat YOffset = scrollView.contentOffset.y;
    NSLog(@"%f",scrollView.contentOffset.y);
    CGFloat width = self.view.frame.size.width;
    if (YOffset < 0) {
        CGFloat allOffset = headerHeght + ABS(YOffset);
        CGFloat scale = allOffset / headerHeght ;
        self.headerIma.frame =  CGRectMake(- (width * scale - width) / 2, YOffset, width * scale, allOffset);
    }
}