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

Swift version

if let visibleRows = tableView.indexPathsForVisibleRows {
    let visibleSections = visibleRows.map({$0.section})
}

Answer 2

Swift 4 and Swift 5

extension UITableView {

    func returnVisibleCellsIndexes() -> [IndexPath] {
        var indexes = [IndexPath]()
        for cell in self.visibleCells {
            if let indexpath = self.returnIndexPath(cell: cell) {
                indexes.append(indexpath)
            }
        }
        return indexes
    }
    func returnIndexPath(cell: UITableViewCell) -> IndexPath?{
        guard let indexPath = self.indexPath(for: cell) else {
            return nil
        }
        return indexPath
    }
    
    func returnVisibleCells() -> [UITableViewCell]{
        let visiblecell = self.visibleCells
        return visiblecell
    }
    
}

How to use

  
    let visibleCellsIndexes = self.tableView.returnVisibleCellsIndexes()
    visibleCellsIndexes.forEach { (indexpath) in

            print(indexpath.section)

     }

Answer 3

for (NSUInteger section = 0; section < self.tableView.numberOfSections; ++section) {
    UIView *headerView = [self.tableView headerViewForSection:section];
    if (headerView.window) {
        NSLog(@"its visible");
    }
}

Answer 4

Or the really easy way would be to take advantage of valueForKeyPath and the NSSet class:

NSSet *visibleSections = [NSSet setWithArray:[[self.tableView indexPathsForVisibleRows] valueForKey:@"section"]];

Basically you get an array of the section values in the visible rows and then populate a set with this to remove duplicates.

Answer 5

Extract the sections from the list of visible rows:

NSArray *indexPathsForVisibleRows = [tableView indexPathsForVisibleRows];
NSMutableIndexSet *indexSet = [NSMutableIndexSet indexSet];
for ( NSIndexPath *indexPath in indexPathsForVisibleRows ) {
     [indexSet addIndex:indexPath.section];
}
NSLog(@"indexSet %@",indexSet);
// indexSet <NSMutableIndexSet: 0x11a5c190>[number of indexes: 5 (in 1 ranges), indexes: (9-13)]

Or:

NSArray *indexPathsForVisibleRows = [detailTableView indexPathsForVisibleRows];
NSMutableSet *sectionSet = [NSMutableSet set];
for ( NSIndexPath *indexPath in indexPathsForVisibleRows ) {
    [sectionSet addObject:[NSNumber numberWithInt:indexPath.section]];
}
NSLog(@"sectionSet %@",sectionSet);
// sectionSet {(13, 11, 9, 10, 12 )}

Answer 6

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];
}