How to get a UITableView's visible sections?

Question

UITableView provides the methods indexPathsForVisibleRows and visibleCells, but how can I get the visible sections?

Answer 1

2 step solution to get the visible sections in a UITableView:

1) Add the header views to a mutable array in viewForHeaderInSection
2) Update the array when the tableview scrolls in scrollViewDidScroll

note the use of the tag property to hold the section number

@property (nonatomic, strong, readwrite) NSMutableArray *headerArray;

- (UIView *)tableView:(UITableView *)tableView viewForHeaderInSection:(NSInteger)section {
    UIView *headerView = [[UIView alloc] initWithFrame:CGRectMake(0, 0, tableView.bounds.size.width, 40)];
    headerView.backgroundColor = [UIColor greenColor];
    headerView.tag = section;
    [_headerArray addObject:headerView];
    return headerView;
}

- (void)scrollViewDidScroll:(UIScrollView *)scrollView {
    [self updateHeaderArray];
    NSLog(@"------------");
    for (UIView *view in _headerArray) {
        NSLog(@"visible section:%d", view.tag);
    }
}

- (void)updateHeaderArray {
    // remove invisible section headers
    NSMutableArray *removeArray = [NSMutableArray array];
    CGRect containerRect = CGRectMake(_tableView.contentOffset.x, _tableView.contentOffset.y,
                                      _tableView.frame.size.width, _tableView.frame.size.height);
    for (UIView *header in _headerArray) {
        if (!CGRectIntersectsRect(header.frame, containerRect)) {
            [removeArray addObject:header];
        }
    }
    [_headerArray removeObjectsInArray:removeArray];
}