1.UIScrollView设置contentInset的top 且设置位置 必须在最前面放后面有问题 以后再说
2.头部就是在UIScrollView之上
3.在scrollView代理方法中判断offset

contentInset 必须在前面

- (BaseTableView *)mainView
{
    if (!_mainView) {
        BaseTableView *tableView = [[BaseTableView alloc]initWithFrame:CGRectMake(0, 0, WIDTH, HEIGHT - kCustomTabBarHeight) style:UITableViewStylePlain];
        tableView.contentInset = UIEdgeInsetsMake(kContentInsetTop, 0, 0, 0);
        tableView.scrollIndicatorInsets = tableView.contentInset;
        [self.view addSubview:tableView];
        tableView.delegate = self;
        tableView.dataSource = self;
        tableView.tableFooterView = [UIView new];
        [tableView registerClass:[UITableViewCell class] forCellReuseIdentifier:@"Cell"];
        tableView.separatorStyle = UITableViewCellSeparatorStyleNone;
        tableView.backgroundColor = kColorBGTinyBlue;
        if (@available(iOS 11.0, *))
        {
            tableView.contentInsetAdjustmentBehavior = UIScrollViewContentInsetAdjustmentNever;
            tableView.estimatedRowHeight = 0;
            tableView.estimatedSectionFooterHeight = 0;
            tableView.estimatedSectionHeaderHeight = 0;
        }
        else
        {
            self.automaticallyAdjustsScrollViewInsets = NO;
        }
        tableView.rowHeight = HEIGHT - kCustomTabBarHeight;
        tableView.showsVerticalScrollIndicator = NO;
        _mainView = tableView;
    }
    return _mainView;
}

flexView

//头部可伸缩模块
@property(nonatomic,strong)UIImageView *flexView;
- (UIImageView *)flexView
{
    if (!_flexView) {
        UIImageView *iv = [[UIImageView alloc]init];
        [self.view addSubview:iv];
        iv.clipsToBounds = YES;
        iv.frame = CGRectMake(0, 0, WIDTH, kContentInsetTop);
        [iv sd_setImageWithURL:@"https://ss0.bdstatic.com/70cFvHSh_Q1YnxGkpoWK1HF6hhy/it/u=2141197356,630198876&fm=11&gp=0.jpg".wppURL];
        _flexView = iv;
    }
    return _flexView;
}

1.为了能到指定位置 不然会有偏移
dispatch_async(dispatch_get_main_queue(), ^{
    [self.mainView setContentOffset:CGPointMake(0, -kHeaderHeight)];
});

scrollView代理方法
CGFloat offset = scrollView.contentOffset.y + scrollView.contentInset.top;
//伸缩
if (offset <= 0) {
    self.flexView.top = 0;
    self.flexView.height = fabs(offset) + kContentInsetTop;
    CGFloat percent = self.flexView.height / kContentInsetTop;
    //宽度整体扩大
    self.flexView.width = WIDTH * percent;
    self.flexView.left = - (WIDTH * (percent - 1) * 0.5);
} else {
    CGFloat flexShowHeight = kStatusBarHeight + 30*ADAPTER_WIDTH;
    CGFloat flexCriticalPoint = kContentInsetTop - flexShowHeight;
    CGFloat minOffset = MIN(offset, flexCriticalPoint);
    self.flexView.top = -minOffset;
    self.flexView.height = kContentInsetTop;
    //宽度整体恢复
    self.flexView.width = WIDTH;
    self.flexView.left = 0;
}

状态栏

_statusBarStyle = (progress < 0.5) ?UIStatusBarStyleDefault:UIStatusBarStyleLightContent;
//主动更新状态栏
[self.navigationController setNeedsStatusBarAppearanceUpdate];