需求：

1. UITableView 右侧有索引
2. sectionHeader禁止悬浮
   3.点击索引，sectionHeader在最上方正常显示

解决方案

1. UITableView 右侧有索引 所以只能选择plain模式不能选择Grouped
   2.plain模式的sectionHeader是悬浮的，滚动时候永远在最顶端，直到下个sectionHeader显示到顶端。
   解决：重写scrollView滚动代理方法

-(void)scrollViewDidScroll:(UIScrollView *)scrollView {
    if (scrollView == self.tableView)
    {
        CGFloat sectionHeaderHeight = 44;  //自定义的sectionHeaderHeight
        if (scrollView.contentOffset.y<=sectionHeaderHeight && scrollView.contentOffset.y>=0) {
            scrollView.contentInset = UIEdgeInsetsMake(-scrollView.contentOffset.y, 0, 0, 0);
        } else if (scrollView.contentOffset.y>=sectionHeaderHeight) {
            scrollView.contentInset = UIEdgeInsetsMake(-sectionHeaderHeight, 0, 0, 0);
        }
    }
}

3.重写完后发现，点右侧索引，sectionHeader是不显示的，只显示第一个row内容
解决： 找到点击索引方法，增加标示，告知scrollView不需要更改contentInset

-(NSInteger)tableView:(UITableView *)tableView sectionForSectionIndexTitle:(NSString *)title atIndex:(NSInteger)index{
    _doNotChangeOffSet = YES;
    // 获取所点目录对应的indexPath值
    NSIndexPath *selectIndexPath = [NSIndexPath indexPathForRow:0  inSection:index];
    // 让table滚动到对应的indexPath位置
    [tableView scrollToRowAtIndexPath:selectIndexPath atScrollPosition:UITableViewScrollPositionBottom animated:NO];
    _doNotChangeOffSet = NO;
    return index;
}

-(void)scrollViewDidScroll:(UIScrollView *)scrollView {
    if (scrollView == self.tableView)
    {
        if (_doNotChangeOffSet) {
            scrollView.contentInset = UIEdgeInsetsMake(0, 0, 0, 0);
            return;
        }
        CGFloat sectionHeaderHeight = 44;  //自定义的sectionHeaderHeight
        if (scrollView.contentOffset.y<=sectionHeaderHeight && scrollView.contentOffset.y>=0) {
            scrollView.contentInset = UIEdgeInsetsMake(-scrollView.contentOffset.y, 0, 0, 0);
        } else if (scrollView.contentOffset.y>=sectionHeaderHeight) {
            scrollView.contentInset = UIEdgeInsetsMake(-sectionHeaderHeight, 0, 0, 0);
        }
    }
}

完美解决。