让中间的cell高亮

- (void)scrollViewDidScroll:(UIScrollView *)scrollView
{
    [[tableView visibleCells] makeObjectsPerformSelector:@selector(setHighlighted:) withObject:[NSNumber numberWithBool:NO]];

    CGPoint center = CGPointMake(0, scrollView.contentOffset.y+(int)(scrollView.frame.size.height/2));
    NSIndexPath *cellIndexPath = [tableView indexPathForRowAtPoint:center];
    UITableViewCell *cell = [tableView cellForRowAtIndexPath:cellIndexPath];
    [cell setHighlighted:YES];
}